Qiming Wang's blog
https://imechanica.org/blog/21855
enEvent of ASME Technical Committee on Mechanics of Soft Materials 2020
https://imechanica.org/node/24715
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>Dear Colleagues, </span></p>
<p> We cordially invite you to participate in an event of ASME Technical Committee on Mechanics of Soft Materials 2020. The detailed agenda is enclosed. <br /></p><p class="MsoNormal" align="center"><strong><span>Event of ASME Technical Committee on Mechanics of Soft Materials 2020:<br />live symposium and committee meeting</span></strong></p>
<p class="MsoNormal"><strong><span>Organizer</span></strong><span>: ASME Technical Committee on Mechanics of Soft Materials, including Sung Hoon Kang (Chair, JHU), Qiming Wang (Vice-chair, USC), Victor Lefevre (Secretary, Northwestern), and Yuhang Hu (Editor, Gatech)</span></p>
<p class="MsoNormal"><strong><span>Date</span></strong><span>: Nov 15, 2020, 12 pm-6 pm EST (9 am-3 pm PST)</span></p>
<p class="MsoNormal"><strong><span>Link</span></strong><span>: </span><a href="https://usc.zoom.us/j/4877520911" target="_blank" rel="noopener noreferrer" data-saferedirecturl="https://www.google.com/url?q=https://usc.zoom.us/j/4877520911&source=gmail&ust=1605043941956000&usg=AFQjCNFXsFXz2SQJHE3jg4VCs0Es8O_6MA"><span>https://usc.zoom.us/j/4877520911</span></a><span> <strong>Meeting ID</strong>: 487 752 0911</span></p>
<p class="MsoNormal"><strong><span>Session 1</span></strong><span>: Understanding elastomer networks</span></p>
<p class="MsoNormal"><strong><span>Chair</span></strong><span>: Qiming Wang, Yuhang Hu</span></p>
<p class="MsoNormal"><strong><span>Time</span></strong><span>: 12-2:20 pm EST, Nov 15 2020</span></p>
<p class="MsoNormal"><span>12-12:40</span></p>
<p class="MsoNormal"><strong><span>Invited keynote speaker</span></strong><span>: Sanjay Govindjee (UC Berkeley)</span></p>
<p class="MsoNormal"><span>Title: Soft and Semi-Soft Elasticity for Liquid Crystal Elastomers: An Overview</span></p>
<p class="MsoNormal"><span>12:40-1</span></p>
<p class="MsoNormal"><span>Shaoting Lin (MIT)</span></p>
<p class="MsoNormal"><span>Title: </span><span>Universal Fracture of Polymer Networks with Topological Defects</span></p>
<p class="MsoNormal"><span>1-1:20</span></p>
<p class="MsoNormal"><span>Nikolaos Bouklas (Cornell)</span></p>
<p class="MsoNormal"><span>Title: Damage and fracture in polydisperse elastomer networks</span></p>
<p class="MsoNormal"><span>1:20-1:40</span></p>
<p class="MsoNormal"><span>Qiming Wang (USC)</span></p>
<p class="MsoNormal"><span>Title: </span><span>Mechanics of Self-Healing Thermoplastic Elastomers</span></p>
<p class="MsoNormal"><span>1:40-2</span></p>
<p class="MsoNormal"><span>Pratik Khandagale (CMU)</span></p>
<p class="MsoNormal"><span>Title: Statistical Field Theory Model for Elastomers</span></p>
<p class="MsoNormal"><span>2-2:20</span></p>
<p class="MsoNormal"><span>Pedro Peralta (ASU)</span></p>
<p class="MsoNormal"><span>Title: Effects of High Pressure on Structural Evolution of Polyurea: An In-Situ Energy Dispersive X-Ray Diffraction Study</span></p>
<p class="MsoNormal"><strong><span>Session 2</span></strong><span>: Stimuli-responsive soft materials</span></p>
<p class="MsoNormal"><strong><span>Chair</span></strong><span>: Sung Hoon Kang, Victor Lefevre</span></p>
<p class="MsoNormal"><strong><span>Time</span></strong><span>: 2:30-4:50 pm EST, Nov 15 2020</span></p>
<p class="MsoNormal"><span>2:30-3:10</span></p>
<p class="MsoNormal"><strong><span>Invited keynote speaker</span></strong><span>: Shengqiang Cai (UCSD)</span></p>
<p class="MsoNormal"><span>Title: </span><span>Mechanics of Liquid Crystal Elastomer</span></p>
<p class="MsoNormal"><span>3:10-3:30</span></p>
<p class="MsoNormal"><span>Sung Hoon Kang (JHU)</span></p>
<p class="MsoNormal"><span>Title: Strain Rate-Adaptive Extreme Energy Absorption via Architected Liquid-Crystalline Elastomers</span></p>
<p class="MsoNormal"><span>3:30-3:50</span></p>
<p class="MsoNormal"><span>Christopher Cooley (Oakland)</span></p>
<p class="MsoNormal"><span>Title: Nonlinear Dynamics of a Dielectric Elastomer Membrane Under Compressive Loading</span></p>
<p class="MsoNormal"><span>3:50-4:10</span></p>
<p class="MsoNormal"><span>Victor Lefevre (Northwestern)</span></p>
<p class="MsoNormal"><span>Title: Electroelastic Response of Isotropic Dielectric Elastomer Composites with Deformation-Dependent Apparent-Permittivity Matrix</span></p>
<p class="MsoNormal"><span>4:10-4:30</span></p>
<p class="MsoNormal"><span>Kiana Naghibzadeh (CMU)</span></p>
<p class="MsoNormal"><span>Title: Modeling of Surface Growth Using an Eulerian Approach</span></p>
<p class="MsoNormal"><span>4:30-4:50</span></p>
<p class="MsoNormal"><span>Dongjing He (Gatech)</span></p>
<p class="MsoNormal"><span>Title: Rate-Dependent Indentation Adhesion of Hydrogel</span></p>
<p class="MsoNormal"><strong><span>Session 3</span></strong><span>: Committee meeting for ASME Technical Committee on Mechanics of Soft Materials</span></p>
<p class="MsoNormal"><strong><span>Chair</span></strong><span>: Qiming Wang, Victor Lefevre, Yuhang Hu</span></p>
<p class="MsoNormal"><strong><span>Time</span></strong><span>: 5-6 pm EST, Nov 15 2020</span></p>
<p class="MsoNormal"><span>Topics:</span></p>
<p><span>1.<span> </span></span><span>Topics of ASME IMECE 2021 symposium on mechanics of soft materials (MOSM)</span></p>
<p><span>2.<span> </span></span><span>Nomination for the new Editor for ASME Technical Committee on MOSM</span></p>
<p> Please feel free to forward the agenda to your friends, colleagues, and students. Hope to see you in the zoom room on Nov 15. Thank you. Best regards, ASME Technical Committee on Mechanics of Soft Materials: Chair: Sung Hoon Kang (JHU)Vice-chair: Qiming Wang (USC)Secretary: Victor Lefevre (Northwestern)Editor: Yuhang Hu (Gatech)</p>
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</div></div></div>Mon, 09 Nov 2020 21:41:50 +0000Qiming Wang24715 at https://imechanica.orghttps://imechanica.org/node/24715#commentshttps://imechanica.org/crss/node/24715Journal Club for April 2019: Self-Healing Soft Materials: from Theoretical Modeling to Additive Manufacturing
https://imechanica.org/node/23207
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/1596">jClub</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><strong>Journal Club for April 2019: Self-Healing Soft Materials: from Theoretical Modeling to Additive Manufacturing</strong></p>
<p>Qiming Wang</p>
<p>University of Southern California</p>
<p><strong>1. Introduction</strong></p>
<p>Self-healing polymers have been revolutionizing the man-made engineering society via bringing in the autonomous intelligence that widely exists in Nature. Self-healing polymers have been applied to a wide range of engineering applications, including flexible electronics [1], energy storage [2], biomaterials [3], and robotics [4]. Motivated by these applications, various self-healing polymers have been synthesized during the past years [5-9]. They typically fall into two categories. The first category is “extrinsic self-healing” that harnesses encapsulates of curing agents [10,11]. The second category is “intrinsic self-healing” that harnesses dynamic bonds, such as dynamic covalent bonds [12-15], hydrogen bonds [16,17], and ionic bonds [18,19]. The dynamic bonds can autonomously reform after fractures or dissociations. This blog entry primarily focuses on the second category. </p>
<p>Despite the success in syntheses and applications, existing self-healing polymers are facing two critical bottlenecks. The first bottleneck is in the theoretical modeling of interfacial healing behavior [5]. Back in the 1980s, scaling models were proposed for the interpenetration of polymer melts [20,21]. After entering the 21st century, molecular dynamics simulations were employed to understand healing behaviors of polymers [22,23]. Although bulk healing [24,25] and high-temperature welding [26] have been modeled in recent years, how to analytically model the interfacial healing of self-healing polymers is still elusive. The missing of this theoretical understanding would significantly drag down the innovation of self-healing polymers to achieve optimal healing performance. </p>
<p>The second bottleneck is in the 3D-shaping method for self-healing polymers. A number of promising applications of self-healing polymers demand complex 2D/3D architectures, such as robotics [27], structural materials [28,29], architected electronics [30], and biomedical devices [3]. However, the architecture demand of self-healing polymers has not been sufficiently fulfilled, because existing 3D methods of shaping self-healing polymers are limited to molding [4,31] and direct-writing [32-34]. </p>
<p>This blog entry outlines recent research efforts of Qiming Wang group at the University of Southern California in unblocking the above two bottlenecks: theoretical modeling [35-39] and additive manufacturing [40] of self-healing polymers. Challenges and opportunities are highlighted at the end of the blog. </p>
<p>Jumping out of this blog, we would like to cast a vision on the field of solid mechanics shown in Fig. 1. Promoted by the US Navy after World War II, Fracture Mechanics enjoyed a golden era in the 20th century [41]. Question: several decades later when people look back, will they consider the 21st century to be the golden era of Self-Healing Mechanics? How do you think about the status/future of Self-Healing Mechanics? Please share your thoughts in the comment box.</p>
<p><img src="https://imechanica.org/files/Fig1_2.jpg" alt="" width="852" height="258" /></p>
<p>Figure 1. Development of Fracture Mechanics and Self-Healing Mechanics. </p>
<p><strong>2. Theoretical modeling of self-healing polymers </strong></p>
<p>We consider the healing process of a polymer network linked by dynamic bonds shown in Fig. 2A. The polymer is cut into two parts and then contact back. After a period of healing time, the sample is stretched until rupture. The self-healed sample is composed of two segments (Fig. 2A): a small “self-healed segment” with re-bridged polymer chains (purple) and two “virgin segments” with intact polymer networks (light pink). The modeling effort is devoted to theoretically quantifying the relationship between the healing percentage and the healing time. The healing percentage is indicated by the ratio between tensile strengths of the healed and the original samples, because most of the researchers in the self-healing community use the tensile strength as the indicator [5-9]. </p>
<p><img src="https://imechanica.org/files/Fig2_2.jpg" alt="" width="852" height="320" /></p>
<p>Figure 2. (A) Healing process. (B) Interpenetration network model. (C) Bell-like model for a dynamic bond. (D) Conceptual self-healing model. (E) Diffusion and binding of a polymer chain. (F) Predicted stress-stretch behaviors of original and self-healed polymers. (G) Predicted relation between the healing strength ratio and healing time[37]. </p>
<p><strong>2.1. An interfacial self-healing model</strong></p>
<p>To theoretically model the interfacial healing of self-healing polymers crosslinked by dynamic bonds, we have two technical challenges: (1) how to understand the mechanics of dynamic-bond-linked polymer networks, and (2) how to understand the network evolution during the healing process. To address the first challenge, we employ an interpenetrating network model that many types of networks interpenetrate each other in the material space (Fig. 2B) [42]. Each type of network is composed of polymer chains of the same length and linked by dynamic bonds. The chain-lengths among different networks follow an inhomogeneous statistic distribution. Under stretch, dynamic bonds obey force-dependent chemical kinetics to transform between the associated state and the dissociated state (Fig. 2C). The force-dependent chemical kinetics can be described by a Bell-like model [43]. To address the second challenge, we consider the healing process as a coupled behavior of inter-diffusion of dissociated chains and re-binding of dissociated dynamic bonds (Fig. 2DE). The curvilinear motion of the polymer chain can be explained by a reptation-like model [44,45], and the binding kinetics by the Bell-like model [43]; therefore, the interpenetration of the polymer chain across the fracture interface can be modeled as a diffusion-reaction system [36,37]. After addressing the above two challenges, we can predict stress-strain behaviors of the original and the healed self-healing polymers (Fig. 2F). As the applied stretch increases, more and more dynamic bonds are dissociated, and the corresponding stress increases and then decreases. The maximal stress (tensile strength) is corresponding to the material rupture. With increasing healing time, the tensile strength of the healed polymer increases until reaching a plateau that is the tensile strength of the original polymer. In this way, we can predict the relation between the healing percentage (healed/original strength) and the healing time (Fig. 2G). Our theory can be used to explain self-healing behaviors of polymers crosslinked by various dynamic bonds, such as dynamic covalent bonds [14,15,40], hydrogen bonds [16], and ionic bonds [19,46] (Fig. 3).</p>
<p><img src="https://imechanica.org/files/Fig3_2.jpg" alt="" width="852" height="305" /></p>
<p>Figure 3. Comparison between theoretical and experimental results of self-healing polymers [37]. </p>
<p><strong>2.2. Effect of polymer network architecture </strong></p>
<p>The self-healing model is expected to be extended to explain self-healing polymers with various network architectures [6,47]. Self-healable nanocomposite hydrogel is a good example: polymer chains are linked by multifunctional nanoparticles through ionic bonds [35]. This type of nanocomposite hydrogel can self-heal fractures through chain diffusion and re-binding. We have successfully extended the self-healing model in [37] to explain the healing behavior of nanocomposite hydrogels (Fig. 4A) [36]. </p>
<p><img src="https://imechanica.org/files/Fig4_2.jpg" alt="" width="720" height="346" /></p>
<p>Figure 4. (A) Self-healing model of nanoparticle-linked networks[35,36]. (B) Light-activated healing model [38]. (C) Electrically-induced interfacial bonding model[39]. </p>
<p><strong>2.3. Effect of external stimuli </strong></p>
<p>The self-healing model can also be used to model stimuli-activated healing. Optically healable polymer is a type of self-healing polymer that harnesses external visible or UV lights to activate the self-healing reaction around the fracture interface [48-50]. We consider that light-triggered free radicals around the healing interface can facilitate the interpenetration of polymer chains, thus establishing two groups of diffusion-reaction systems: light-activated production of free radicals and diffusion-binding of polymer chains. In this way, we can theoretically explain the light-activated healing of polymer networks crosslinked by optically-responsive nanoparticles or organic photophores (Fig. 4B) [38]. </p>
<p><strong>2.4. Extend to interfacial bonding of soft materials </strong></p>
<p>Motivated by the pioneering research of Zhao [51,52] and Suo [53-55], the design of tunable/tough bonding between soft materials attracts much attention. We expect that our interfacial self-healing model may be used to provide theoretical explanations for the emerging tough-bonding studies. Taking electrophoresis-induced bonding as an example [39], we consider charged polymers chains are driven by an electric field to move across the interface to interpenetrate into the respective material matrix, and form ionic bonds with chains of opposite charges. A model for the electrically-driven reptation-like motion of polymer chains is formulated. Our theory successfully explains the electrically-induced bonding increase and decrease between charged polymer networks (Fig. 4C) [39]. </p>
<p><strong>3. Additive manufacturing of self-healing polymers</strong></p>
<p>Besides the theoretical effort, we also develop an experimental strategy for photopolymerization-based additive manufacturing (AM) of self-healing elastomers with free-form architectures (Fig. 5) [40]. The strategy relies on a molecularly designed photoelastomer ink with both thiol and disulfide groups, where the former facilitates a thiol-ene photopolymerization during the AM process, and the latter enables a disulfide metathesis reaction during the self-healing process. Using projection microstereolithography systems, we demonstrate rapid AM of single- and multimaterial elastomer structures in various 3D complex geometries within a short time (e.g., 0.6 mm × 15 mm × 15 mm/min=13.5 mm^3/min). The resolution can reach 13.5 µm. These structures can rapidly heal fractures and restore their mechanical strengths to 100%. We also demonstrate additive manufacturing of single- and multimaterial self-healable structures for 3D soft actuators, multiphase composites, and architected electronics [40].</p>
<p><img src="https://imechanica.org/files/Fig5_1.jpg" alt="" width="720" height="353" /></p>
<p>Figure 5. Additive manufacturing of self-healing elastomers. (A) Molecular design of the self-healing elastomer (B) Stereolithography-based additive manufacturing process. (C) Schematics to show the disulfide-bond enabled the self-healing process. (D) The manufactured samples. (E) Self-healing of a shoe pad sample. The healing condition is 2 h at 60°C [40].</p>
<p><strong>4. Challenge and opportunity</strong> </p>
<p>The theoretical modeling and additive manufacturing of self-healing polymers highlight a number of challenges and opportunities in the field of solid mechanics, additive manufacturing, and polymer science. We list some of them as follows. Welcome to share your thoughts in the comment box. </p>
<p><strong>4.1. Learn from Fracture Mechanics</strong></p>
<p>We have learned a number of classic terminologies from the Fracture Mechanics class: stress intensity factor, energy release rate, J integral, HRR field, and many more. Questions for our generation: What new concepts and terminologies in the field of Self-Healing Mechanics can we invent for the next generation to follow? How will these new terminologies impact the emerging engineering practice and the solid mechanics field? </p>
<p>Related Journal Club: Aug 2017, <a href="http://imechanica.org/node/21461#comments">Fracture mechanics of soft dissipative materials</a>, Rong Long (UC Boulder)</p>
<p><strong>4.2. Guide design of novel self-healing polymers</strong></p>
<p>Emerging self-healing polymers are becoming tougher, quicker, and smarter [5-9]. The existing field of self-healing polymers primarily relies on chemical innovations. Questions for mechanicians: How to harness emerging self-healing models to guide the design of novel self-healing polymers? How to theoretically understand new polymer network architectures, new dynamic bonds, and new triggering stimuli? </p>
<p>Related Journal Club: Jan 2018, <a href="http://imechanica.org/node/21978">Recent advances in liquid crystal elastomers</a>, Shengqiang Cai (UCSD)</p>
<p>Related Journal Club: Mar 2019, <a href="https://imechanica.org/node/23127">Fatigue of hydrogels</a>, Ruobing Bai (Caltech)</p>
<p><strong>4.3. Guide design of interfacial bonding of soft materials</strong> </p>
<p>The tough bonding between similar or dissimilar soft materials has been enabling broad applications [51-55]; however, the theoretical understanding has been left behind. Questions for mechanicians: How to harness the emerging diffusion-reaction models of polymer chains to guide the design of novel tunable/tough bonding of soft materials? </p>
<p>Related Journal Club: Dec 2018, <a href="http://imechanica.org/node/22900">Bonding hydrophilic and hydrophobic soft materials for functional soft devices</a>, Qihan Liu (Harvard)</p>
<p><strong>4.4. Harness architectures of self-healing structures </strong> </p>
<p>The emerging additive manufacturing technology brings unprecedented architectures to self-healing polymers. The interaction between self-healing and architecture may enable possibilities for broad applications, such as flexible electronics, robotics, biomedical devices, energy storage devices, and lightweight structures. </p>
<p>Related Journal Club: Feb 2018, <a href="http://imechanica.org/node/22096">HASEL artificial muscles for high-speed, electrically powered, self-healing soft robots</a>, Christoph Keplinger (UC Boulder)</p>
<p>Related Journal Club: Mar 2017, <a href="http://imechanica.org/node/20967">Architected materials</a>, Sung Hoon Kang (JHU)</p>
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</div></div></div>Mon, 01 Apr 2019 06:18:46 +0000Qiming Wang23207 at https://imechanica.orghttps://imechanica.org/node/23207#commentshttps://imechanica.org/crss/node/23207Abstract invitation for the 4th Mini-Symposium on 4M Engineering Materials and Structures of EMI conference 2019
https://imechanica.org/node/23045
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/74">conference</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Dear Colleagues, </p>
<p>We cordially invite you to submit abstracts to the 4th Mini-Symposium on 4M (Modeling of Multiphysics-Multiscale-Multifunctional) Engineering Materials and Structures in the Engineering Mechanics Institute conference 2019 at Caltech during June 18-21, 2019. </p>
<p>Submission link: <a href="http://emi2019.caltech.edu/home">http://emi2019.caltech.edu/home</a></p>
<p>Deadline: Jan 30, 2019</p>
<p><span>The 4th Mini-Symposium on 4M (Modeling of Multiphysics-Multiscale-Multifunctional) Engineering Materials and Structures on behalf of the Engineering Mechanics Institute (EMI) Modeling Inelasticity and Multiscale Behavior (MIMB) Committee at the EMI annual conference 2019</span></p>
<p><span>Recently, there has been increasing interests/foci and developments on the multiphysics-multiscale-multifunctional nature of materials research in several different disciplines. It is because many engineering materials and structures present multiple length/time scale dependent behavior which is coupled with multiphysics phenomena (e.g., kinetic, hydraulic, thermal, electromagnetic, etc.), and are increasingly targeted toward multifunctional characteristics. Even though multiphysics-multiscale problems have long been studied in Mathematics, Physics, and Chemistry, the current excitement is driven heavily by the use of </span>advanced<span> modeling in the applied engineering and science. In addition, multifunctional materials are sought to meet specific requirements (functions) through tailored properties. Smart materials can be considered as multifunctional materials that have the ability to react upon an external stimulus. The introduction of </span>Biomimetics<span> in the material science allows the designing of materials with similar processes as nature does: building from molecules to complete structures (i.e., multiscale). Properly executed modeling of multiphysics-multiscale-multifunctional engineering materials and structures can vastly improve accuracy and efficiency in solutions which were not quite feasible through conventional approaches, in many cases, with very reasonable experimental-computational costs. </span></p>
<p><span>Presentations from various fields are invited on the relevant topics including, but are not limited to:</span></p>
<p><span><strong>Thrust 1</strong>: Multiphysics</span></p>
<ul><li>Coupled (multiphysical<span>) modeling/simulation of engineering materials and structures</span></li>
<li>Materials-structures interaction with environmental effects</li>
<li>Multiphysics coupling of stimuli-responsive smart materials/structures</li>
</ul><p><strong>Thrust 2</strong>: Multiscale</p>
<ul><li>Quasi-continuum and equivalent continuum approaches</li>
<li>Atomistic to continuum coupling</li>
<li>The marriage<span> of discrete medium and continuum mechanics</span></li>
<li>Inelastic behavior and damage-fracture of materials in multiscale</li>
<li>Effects of impurities (inclusions) on mechanical properties of composites</li>
<li>Advanced nanocomposite-nanomaterials systems and nanomechanics</li>
<li>Mechanics of bioinspired materials and structures with hierarchical structures</li>
</ul><p><strong>Thrust 3</strong>: Multifunctional</p>
<ul><li>Multifunctional materials-structures and their constitutive/performance modeling;</li>
<li>Adaptive materials and structures that allow reconfiguration or readjustment of shape, functionality and mechanical properties in response to external stimuli</li>
<li>Self-healing materials such as polymers, composites, and concretes</li>
<li>Mechanics of materials and structures with bioinspired functions</li>
</ul><p>Organizer:</p>
<p>Yong-Rak Kim, University of Nebraska–Lincoln, <a href="mailto:yong-rak.kim@unl.edu">yong-rak.kim@unl.edu</a></p>
<p>Chung Song, University of Nebraska–Lincoln, <a href="mailto:csong8@unl.edu">csong8@unl.edu</a></p>
<p>Huiming Yin, Columbia University, <a href="mailto:hy2251@columbia.edu">hy2251@columbia.edu</a></p>
<p>Qiming Wang, University of Southern California, <a href="mailto:qimingw@usc.edu">qimingw@usc.edu</a></p>
<p>Xiaoyu Song, University of Florida, <a href="mailto:xiaoyu.song@essie.ufl.edu">xiaoyu.song@essie.ufl.edu</a></p>
</div></div></div>Tue, 29 Jan 2019 21:54:52 +0000Qiming Wang23045 at https://imechanica.orghttps://imechanica.org/node/23045#commentshttps://imechanica.org/crss/node/23045Postdoc position in additive manufacturing at the University of Southern California
https://imechanica.org/node/22997
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p class="MsoNormal">A postdoc position is available in the Qiming Wang group at the University of Southern California. The successful candidate is expected to work on the additive manufacturing of architected materials.</p>
<p class="MsoNormal">The candidates with the following research backgrounds are welcome to apply: (1) polymer synthesis and characterization, (2) photopolymerization-based additive manufacturing (e.g., stereolithography, two-photon, PolyJet, and others), and/or (3) mechanics of smart materials and structures. </p>
<p class="MsoNormal">Good oral and written English skills are required.</p>
<p class="MsoNormal">The position has an initial one-year appointment and can be renewed up to 3 years based on performance.</p>
<p class="MsoNormal">Application method: the potential candidate can send a resume, three representative papers, and contact information of three references to Dr. Qiming Wang (<a href="mailto:qimingw@usc.edu">qimingw@usc.edu</a>). More information can be found on the group website: <a href="http://www-bcf.usc.edu/~qimingw/">http://www-bcf.usc.edu/~qimingw/</a>.</p>
</div></div></div>Wed, 09 Jan 2019 20:56:28 +0000Qiming Wang22997 at https://imechanica.orghttps://imechanica.org/node/22997#commentshttps://imechanica.org/crss/node/22997Magnetoactive Acoustic Metamaterials
https://imechanica.org/node/22308
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Kunhao Yu, Nicholas X. Fang, Guoliang Huang, Qiming Wang, <a href="https://www.onlinelibrary.wiley.com/doi/epdf/10.1002/adma.201706348">Magnetoactive Acoustic Metamaterials</a>, Advanced Materials, 1706348, 2018.</p>
<p>Abstract: Acoustic metamaterials with negative constitutive parameters (modulus and/or mass density) have shown great potential in diverse applications ranging from sonic cloaking, abnormal refraction and superlensing, to noise canceling. In conventional acoustic metamaterials, the negative constitutive parameters are engineered via tailored structures with fixed geometries; therefore, the relationships between constitutive parameters and acoustic frequencies are typically fixed to form a 2D phase space once the structures are fabricated. Here, by means of a model system of magnetoactive lattice structures, stimuli‐responsive acoustic metamaterials are demonstrated to be able to extend the 2D phase space to 3D through rapidly and repeatedly switching signs of constitutive parameters with remote magnetic fields. It is shown for the first time that effective modulus can be reversibly switched between positive and negative within controlled frequency regimes through lattice buckling modulated by theoretically predicted magnetic fields. The magnetically-triggered negative‐modulus and cavity‐induced negative density are integrated to achieve flexible switching between single‐negative and double‐negative. This strategy opens promising avenues for remote, rapid, and reversible modulation of acoustic transportation, refraction, imaging, and focusing in subwavelength regimes.</p>
</div></div></div>Wed, 11 Apr 2018 20:04:43 +0000Qiming Wang22308 at https://imechanica.orghttps://imechanica.org/node/22308#commentshttps://imechanica.org/crss/node/22308Highly-stretchable 3D-architected Mechanical Metamaterials
https://imechanica.org/node/20504
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/3568">additive manufacturing</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>Highly-stretchable 3D-architected Mechanical Metamaterials</span></p>
<p>Abstract: Soft materials featuring both 3D free-form architectures and high stretchability are highly desirable for a number of engineering applications ranging from cushion modulators, soft robots to stretchable electronics; however, both the manufacturing and fundamental mechanics are largely elusive. Here, we overcome the manufacturing difficulties and report a class of mechanical metamaterials that not only features 3D free-form lattice architectures but also poses ultrahigh reversible stretchability (strain > 414%), 4 times higher than that of the existing counterparts with the similar complexity of 3D architectures. The microarchitected metamaterials, made of highly stretchable elastomers, are realized through an additive manufacturing technique, projection microstereolithography, and its postprocessing. With the fabricated metamaterials, we reveal their exotic mechanical behaviors: Under large-strain tension, their moduli follow a linear scaling relationship with their densities regardless of architecture types, in sharp contrast to the architecture-dependent modulus power-law of the existing engineering materials; under large-strain compression, they present tunable negative-stiffness that enables ultrahigh energy absorption efficiencies. To harness their extraordinary stretchability and microstructures, we demonstrate that the metamaterials open a number of application avenues in lightweight and flexible structure connectors, ultraefficient dampers, 3D meshed rehabilitation structures and stretchable electronics with designed 3D anisotropic conductivity.</p>
<p>Yanhui Jiang, Qiming Wang, Highly-stretchable 3D-architected Mechanical Metamaterials, Scientific Reports, 6, 34147, 2016.</p>
<p><a href="http://www-bcf.usc.edu/~qimingw/Papers/31_elastomerlattice.pdf">PDF</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/31_SI.pdf">SI</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/31_SM01.mov">Movie 1</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/31_SM02.mov">Movie 2</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/31_SM03.mov">Movie 3</a>,<a href="http://www-bcf.usc.edu/~qimingw/Papers/31_SM04.mov"> Movie 4</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/31_SM05.mov">Movie 5</a>,<a href="http://www-bcf.usc.edu/~qimingw/Papers/31_SM06.mov"> Movie 6</a>. </p>
<p> </p>
</div></div></div>Mon, 24 Oct 2016 05:17:05 +0000Qiming Wang20504 at https://imechanica.orghttps://imechanica.org/node/20504#commentshttps://imechanica.org/crss/node/20504Lightweight Mechanical Metamaterials with Tunable Negative Thermal Expansion
https://imechanica.org/node/20503
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/3568">additive manufacturing</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>Lightweight Mechanical Metamaterials with Tunable Negative Thermal Expansion</span></p>
<p>Abstract: Ice floating on water is a great manifestation of negative thermal expansion (NTE) in nature. The limited examples of natural materials possessing NTE have stimulated research on engineered structures. Previous studies on NTE structures were mostly focused on theoretical design with limited experimental demonstration in two-dimensional planar geometries. In this work, aided with multimaterial projection microstereolithography, we experimentally fabricate lightweight multimaterial lattices that exhibit significant negative thermal expansion in three directions and over a temperature range of 170 degrees. Such NTE is induced by the structural interaction of material components with distinct thermal expansion coefficients. The NTE can be tuned over a large range by varying the thermal expansion coefficient difference between constituent beams and geometrical arrangements. Our experimental results match qualitatively with a simple scaling law and quantitatively with computational models.</p>
<p>Qiming Wang, Julie A. Jackson, Qi Ge, Jonathan B. Hopkins, Christopher M. Spadaccini, Nicholas X. Fang, Lightweight Mechanical Metamaterials with Tunable Negative Thermal Expansion, Physical Review Letters, 117, 175901, 2016.</p>
<p><a href="http://www-bcf.usc.edu/~qimingw/Papers/32_NTE.pdf">PDF</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/32_SI.pdf">SI</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/32_SM01.wmv">Movie 1</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/32_SM02.wmv">Movie 2</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/32_SM03.wmv">Movie 3</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/32_SM04.wmv">Movie 4</a>. </p>
</div></div></div>Mon, 24 Oct 2016 05:04:03 +0000Qiming Wang20503 at https://imechanica.orghttps://imechanica.org/node/20503#commentshttps://imechanica.org/crss/node/20503A Constitutive Model of Nanocomposite Hydrogels with Nanoparticle Crosslinkers
https://imechanica.org/node/19775
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>A Constitutive Model of Nanocomposite Hydrogels with Nanoparticle Crosslinkers</p>
<p>Qiming Wang, Zheming Gao</p>
<p>Email: <a href="mailto:qimingw@usc.edu">qimingw@usc.edu</a></p>
<p>Abstract: Nanocomposite hydrogels with only nanoparticle crosslinkers exhibit extraordinarily higher stretchability and toughness than the conventional organically crosslinked hydrogels, thus showing great potential in the applications of artificial muscles and cartilages. Despite their potential, the microscopic mechanics details underlying their mechanical performance have remained largely elusive. Here, we develop a constitutive model of the nanoparticle hydrogels to elucidate the microscopic mechanics behaviors, including the microarchitecture and evolution of the nanoparticle crosslinked polymer chains during the mechanical deformation. The constitutive model enables us to understand the Mullins effect of the nanocomposite hydrogels, and the effects of nanoparticle concentrations and sizes on their cyclic stress-strain behaviors. The theory is quantitatively validated by the tensile tests on a nanocomposite hydrogel with nanosilica crosslinkers. The theory can also be extended to explain the mechanical behaviors of existing hydrogels with nanoclay crosslinkers, and the necking instability of the composite hydrogels with both nanoparticle crosslinkers and organic crosslinkers. We expect that this constitutive model can be further exploited to reveal mechanics behaviors of novel particle-polymer chain interactions, and to design unprecedented hydrogels with both high stretchability and toughness. </p>
<p>Journal of the Mechanics and Physics of Solids, 2016. <a href="http://www.sciencedirect.com/science/article/pii/S0022509615303318">doi:10.1016/j.jmps.2016.04.011</a></p>
<p><a href="http://www-bcf.usc.edu/~qimingw/Papers/30_nanohydrogel.pdf">PDF</a>. </p>
</div></div></div>Sun, 24 Apr 2016 03:56:05 +0000Qiming Wang19775 at https://imechanica.orghttps://imechanica.org/node/19775#commentshttps://imechanica.org/crss/node/19775Beyond Wrinkles: Multimodal Surface Instabilities for Multifunctional Patterning
https://imechanica.org/node/19774
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Beyond Wrinkles: Multimodal Surface Instability for Multifunctional Patterning</p>
<p>Qiming Wang, Xuanhe Zhao</p>
<p>Email: <a href="mailto:qimingw@usc.edu">qimingw@usc.edu</a>, <a href="mailto:zhaox@mit.edu">zhaox@mit.edu</a></p>
<p>Abstract: Biological surfaces display fascinating topographic patterns such as corrugated blood cells and wrinkled dog skin. These patterns have inspired an emerging technology in materials science and engineering to create self-organized surface patterns by harnessing mechanical instabilities. Compared with patterns generated by conventional lithography, surface instability patterns are low-cost, are easy to fabricate, and can be dynamically controlled by tuning various physical stimuli—offering new opportunities in materials and device engineering across multiple length scales. This article provides a systematic review on the fundamental mechanisms and innovative functions of surface instability patterns by categorizing various modes of instabilities into a quantitatively defined thermodynamic phase diagram, and by highlighting their engineering and biological applications.</p>
<p><a href="http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10177970&fileId=S0883769415003383">MRS Bulletin, 41, 115-122 (2016)</a>.</p>
<p><a href="http://www-bcf.usc.edu/~qimingw/Papers/29_instabilityreview.pdf">PDF</a>. </p>
</div></div></div>Sun, 24 Apr 2016 03:46:47 +0000Qiming Wang19774 at https://imechanica.orghttps://imechanica.org/node/19774#commentshttps://imechanica.org/crss/node/19774Call for abstract for APS March 2016 Focus Session Physics of Bioinspired Materials, Deadline November 6 2015
https://imechanica.org/node/18836
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/74">conference</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/10737">APS</a></div><div class="field-item odd"><a href="/taxonomy/term/6321">bioinspired materials</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p class="MsoNormal">Dear Colleagues,</p>
<p class="MsoNormal">The upcoming APS March Meeting 2016 will take place at Baltimore, MD during March 14-18 2016. Here, we would like to invite you to contribute to a focus session called “Physics of Bioinspired Materials”. </p>
<p class="MsoNormal"><strong>Session title</strong>: 2.1.3 (same as 4.1.17) Physics of Bioinspired Materials (GSOFT/DBIO)</p>
<p class="MsoNormal"><strong>Link</strong>: <a href="http://www.aps.org/meetings/march/scientific/focus.cfm#213">http://www.aps.org/meetings/march/scientific/focus.cfm#213</a></p>
<p class="MsoNormal"><span><strong><span>Description of the topic:</span></strong></span> Natural materials are synthesized by gene-guided assembly of molecular components into hierarchical structures, and exhibit remarkable properties or functions under the activation of neuron or hormone. Human beings have long been inspired from the natural systems and distilled various principles to design bioinspired systems with superior properties. Recent years have witnessed a wave of renewed interest in designing bioinspired materials and structures especially accompanying with the rapid development of modern fabrication technology, such as nanofabrication and 3D printing. For example, a number of novel top-down or bottom-up fabrication approaches have been developed to tailor materials into bioinspired structures that enable unprecedented properties such as ultra-lightweight, ultra-tough, ultra-strong, ultra-stretchable, ultra-diffusive, and ultra-conductive. Moreover, various activation mechanisms have been introduced to trigger biomimetic movements or deformations, thus resulting in ultra-active, ultra-adaptable and stimuli-sensitive materials. Understanding the physics governing formation of novel bioinspired structures and their stimuli-responsive behaviors is the key challenge to advance their design and uncover their potential. The goal of this session is to create a platform for experts working on bioinspired materials, to discuss about the novel physics problems across different length scales and properties. We expect this session will become a unique forum that not only p<span>rovides the physical understanding of bioinspired materials, but also offers physical insights to advance the design of future bioinspired systems for broad applications by addressing the current scientific and technological challenges. </span></p>
<p><strong><span><span>Topics will include:</span></span></strong>
</p><ul><li><span>Physics of self-assembly or self-organization approaches for bioinspired materials</span></li>
<li><span>Physics oftop-down and/or bottom-up approaches for making hierarchical structures</span></li>
<li><span>Physics of 3D printing of biomaterials or bioinspired structures</span></li>
<li><span>Structure-function relationships in bioinspired materials/structures</span></li>
<li><span>Physics of stimuli-responsive behaviors of bioinspired materials/structures</span></li>
<li><span>Physics of bioinspired sensing and actuation</span></li>
<li><span>Physics of bioinspired surfaces and interfaces</span></li>
</ul><p class="MsoNormal"><strong>Abstract submission: <a href="http://abstracts.aps.org/">http://abstracts.aps.org/</a> </strong></p>
<p class="MsoNormal"><strong>Deadline</strong>: <strong>November 6, 2015, 5:00 p.m. EST</strong></p>
<p class="MsoNormal">We will try to organize a unique and successful session that brings together world-wide expects in the field of “physics of bioinspired materials”, and delivers high-quality talks to discuss the cutting-edge problems and challenges. <span>We are looking forward to your contribution and participation.</span><span> </span></p>
<p class="MsoNormal">If you have any questions, please do not hesitate to contact us. <strong> </strong></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Sincerely,</p>
<p class="MsoNormal">Sung Hoon Kang (Johns Hopkins University, Email: <a href="mailto:shkang@jhu.edu">shkang@jhu.edu</a>)</p>
<p class="MsoNormal">Qiming Wang (University of Southern California, Email: <a href="mailto:qimingw@usc.edu">qimingw@usc.edu</a>)</p>
</div></div></div>Fri, 11 Sep 2015 04:52:16 +0000Qiming Wang18836 at https://imechanica.orghttps://imechanica.org/node/18836#commentshttps://imechanica.org/crss/node/18836A Three-Dimensional Phase Diagram of Growth-Induced Surface Instabilities
https://imechanica.org/node/18537
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="http://www-bcf.usc.edu/~qimingw/Papers/27_phasediagram2.pdf">A Three-Dimensional Phase Diagram of Growth-Induced Surface Instabilities</a></p>
<p><a href="http://imechanica.org/user/21855">Qiming Wang</a>, <a href="http://imechanica.org/user/51">Xuanhe Zhao</a></p>
<p>A variety of fascinating morphological patterns arise on surfaces of growing, developing or aging tissues, organs and microorganism colonies. These patterns can be classified into creases, wrinkles, folds, period-doubles, ridges and delaminated-buckles according to their distinctive topographical characteristics. One universal mechanism for the pattern formation has been long believed to be the mismatch strains between biological layers with different expanding or shrinking rates, which induce mechanical instabilities. However, a general model that accounts for the formation and evolution of these various surface-instability patterns still does not exist. Here, we take biological structures at their current states as thermodynamic systems, treat each instability-pattern as a thermodynamic phase, and construct a unified phase diagram that can quantitatively predict various types of growth-induced surface instabilities. We further validate the phase diagram with our experiments on surface instabilities induced by mismatch strains as well as the reported data on growth-induced instabilities in various biological systems. The predicted wavelengths and amplitudes of various instability patterns match well with our experimental data. It is expected that the unified phase diagram will not only advance the understanding of biological morphogenesis, but also significantly facilitate the design of new materials and structures by rationally harnessing surface instabilities.</p>
<p><a href="http://www-bcf.usc.edu/~qimingw/Papers/27_phasediagram2.pdf">PDF</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/27_SI.pdf">Suppoting information</a>.</p>
<p><a href="http://www.nature.com/srep/2015/150309/srep08887/full/srep08887.html?WT.ec_id=SREP-20150310">Scientific Reports, 5, 8887 (2015)</a>. </p>
<p>Related Publication: <a href="http://www-bcf.usc.edu/~qimingw/Papers/23_phasediagram01.pdf">Phase Diagrams of Instabilities in Compressed Film-Substrate Systems, Journal of Applied Mechanics</a>, 81, 051004 (2014). <a href="http://imechanica.org/node/15794">iMechanica post link</a>. <a href="http://imechanica.org/node/17794">2015 Journal of Applied Mechanics Award</a>.</p>
</div></div></div>Sat, 04 Jul 2015 06:42:15 +0000Qiming Wang18537 at https://imechanica.orghttps://imechanica.org/node/18537#commentshttps://imechanica.org/crss/node/18537Mechanics of Mechanochemically Responsive Elastomers
https://imechanica.org/node/18536
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p> </p>
<p><a href="http://www-bcf.usc.edu/~qimingw/Papers/28_mechanochemo.pdf">Mechanics of Mechanochemically Responsive Elastomers</a></p>
<p><a href="http://imechanica.org/user/21855">Qiming Wang</a>, Gregory R. Gossweiler, Stephen L. Craig, <a href="http://imechanica.org/user/51">Xuanhe Zhao</a></p>
<p>Mechanochemically responsive (MCR) polymers have been synthesized by incorporating mechanophores – molecules whose chemical reactions are triggered by mechanical force – into conventional polymer networks. Deformation of the MCR polymers applies force on the mechanophores and triggers their reactions, which manifest as phenomena such as changing colors, varying fluorescence and releasing molecules. While the activation of most existing MCR polymers requires irreversible plastic deformation or fracture of the polymers, we covalently coupled mechanophores into the backbone chains of elastomer networks, achieving MCR elastomers that can be repeatedly activated over multiple cycles of large and reversible deformations. This paper reports a microphysical model of MCR elastomers, which quantitatively captures the interplay between the macroscopic deformation of the MCR elastomers and the reversible activation of mechanophores on polymer chains with non-uniform lengths. Our model consistently predicts both the stress-strain behaviors and the color or fluorescence variation of the MCR elastomers under large deformations. We quantitatively explain that MCR elastomers with time-independent stress-strain behaviors can present time-dependent variation of color or fluorescence due to the kinetics of mechanophore activation and that MCR elastomers with different chain-length distributions can exhibit similar stress-strain behaviors but very different colors or fluorescence. Implementing the model into ABAQUS subroutine further demonstrates our model’s capability in guiding the design of MCR elastomeric devices for applications such as large-strain imaging and color and fluorescence displays.</p>
<p><a href="http://www-bcf.usc.edu/~qimingw/Papers/28_mechanochemo.pdf">PDF</a>, <a href="http://www-bcf.usc.edu/~qimingw/Papers/28_code.txt">Subroutine code</a></p>
<p><a href="http://www.sciencedirect.com/science/article/pii/S002250961500112X">Journal of the Mechanics and Physics of Solids</a>, in press.</p>
<p>Related publication: <a href="http://www-bcf.usc.edu/~qimingw/Papers/25_camouflage.pdf">Cephalopod-inspired Design of Electro-mechano-chemically Responsive Elastomers for On-demand Fluorescent Patterning</a>, Nature Communications, 5, 4899 (2014). <a href="http://imechanica.org/node/17282">iMechanica post link</a>. </p>
</div></div></div>Sat, 04 Jul 2015 06:32:30 +0000Qiming Wang18536 at https://imechanica.orghttps://imechanica.org/node/18536#commentshttps://imechanica.org/crss/node/18536Openings at Bioinspired Materials and Structures Lab of USC
https://imechanica.org/node/18239
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/5737">academic job</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p class="MsoNormal"><span><strong>Openings at Bioinspired Materials and Structures Lab of USC</strong></span></p>
<p class="MsoNormal">The <a href="http://web.mit.edu/qmwang/www/index.html">Bioinspired Materials and Structures Laboratory</a> at Civil and Environmental Engineering of University of Southern California is seeking two highly motivated Ph.D. students from 2016 spring or fall semester: one with mechanics background and another with background in microorganism. Our research is focused on mechanics of active materials and structures (physically sensitive materials, soft materials, biomaterials and lightweight structures) and biofouling management (biofilm mechanics, biomedical devices and water treatment). We take experimental, theoretical and computational approaches, and seamlessly integrate modern additive manufacture technology (3D printing) with solid mechanics. The projects will have great potential impact in addressing grand engineering challenges, ranging from better urban infrastructure, clean water, air pollution, carbon sequestration to personalized medicine.</p>
<p class="MsoNormal">Qualified applicants should have a B.S. or M.S. degree in Civil Engineering, Engineering Mechanics, Mechanical Engineering, Physics, Biomedical Engineering, Polymer Science or related fields. Candidates with course or research background in additive manufacture, solid mechanics, structural mechanics/design, mechanics of materials or polymer physics/chemistry are highly encouraged to apply. Proficiency in ABAQUS, SolidWorks or Labview is a plus, but not required. The qualified students (Ph.D. positions) will be provided with full financial support, and systematically trained in clear research paths to be future independent researchers. The potential candidates can refer to the BMSL website (<a href="http://web.mit.edu/qmwang/www/">http://www-bcf.usc.edu/~qimingw/</a>), and send resume and contact information of three references to Dr. Qiming Wang via <a href="mailto:qimingw@usc.edu">qimingw@usc.edu</a>. The positions will be open until filled.</p>
<p class="MsoNormal">Qiming Wang is Assistant Professor of Civil and Environmental Engineering at University of Southern California. Originally from China, he obtained B.S. degree from Fudan University in 2010. Thereafter, he owned Ph.D. degree from Duke University in 2014, and subsequently experienced one-year postdoctoral training at Massachusetts Institute of Technology. He won MRS Graduate Student Award, ASME Best Student Paper Award, NSF-PACAM Fellowship, NIH-Duke Lew Pre-doctoral Fellowship and Kewaunee Student Achievement Award. His research was widely reported by Discovery, Washington Post, BBC Focus, NBC News, Wall Street Journal, Physics Today, NSF News, Duke News, and MIT News.</p>
</div></div></div>Thu, 30 Apr 2015 00:43:13 +0000Qiming Wang18239 at https://imechanica.orghttps://imechanica.org/node/18239#commentshttps://imechanica.org/crss/node/18239Cephalopod-inspired Design of Electro-mechano-chemically Responsive Elastomers for On-demand Fluorescent Patterning
https://imechanica.org/node/17282
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/5996">SAMs Lab research</a></div><div class="field-item odd"><a href="/taxonomy/term/10131">Mechanochemistry</a></div><div class="field-item even"><a href="/taxonomy/term/992">dielectric elastomer</a></div><div class="field-item odd"><a href="/taxonomy/term/10132">wrinkling instability</a></div><div class="field-item even"><a href="/taxonomy/term/10133">stimuli-responsive polymer</a></div><div class="field-item odd"><a href="/taxonomy/term/160">flexible display</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Cephalopod-inspired Design of Electro-mechano-chemically Responsive Elastomers for On-demand Fluorescent Patterning</p>
<p><a href="http://imechanica.org/user/21855">Qiming Wang</a>, Gregory R. Gossweiler, Stephen L. Craig*, <a href="http://imechanica.org/user/51">Xuanhe Zhao</a>*</p>
<p>Cephalopods can display dazzling patterns of colors by selectively contracting muscles to reversibly activate chromatophores – pigment-containing cells under their skins. Inspired by this novel coloring strategy found in nature, we design an electro-mechano-chemically responsive elastomer system that can exhibit a wide variety of fluorescent patterns under the control of electric fields. We covalently couple a stretchable elastomer with mechanochromic molecules, which emit strong fluorescent signals if sufficiently deformed. We then use electric fields to induce various patterns of large deformation on the elastomer surface, which displays versatile fluorescent patterns including lines, circles and letters on demand. Theoretical models are further constructed to predict the electrically-induced fluorescent patterns and to guide the design of this class of elastomers and devices. The material and method open promising avenues for creating flexible devices in soft/wet environments that combine deformation, colorimetric and fluorescent response with topological and chemical changes in response to a single remote signal.</p>
<p>Corresponding email: <a href="mailto:zhaox@mit.edu">zhaox@mit.edu</a>, <a href="mailto:stephen.craig@duke.edu">stephen.craig@duke.edu</a></p>
<p><a href="http://www.nature.com/ncomms/2014/140916/ncomms5899/abs/ncomms5899.html">Nature Communications, 5, 4899 (2014)</a></p>
<p><a href="http://www.web.mit.edu/zhaox/www/papers/68.pdf">PDF</a>, <a href="http://www.web.mit.edu/zhaox/www/papers/68_s.pdf">Supporting Information</a>, <a href="http://www.web.mit.edu/zhaox/www/video/68_SM01.mov">Video 1</a>, <a href="http://www.web.mit.edu/zhaox/www/video/68_SM02.mov">Video 2</a>, <a href="http://www.web.mit.edu/zhaox/www/video/68_SM03.mov">Video 3</a>, <a href="http://www.web.mit.edu/zhaox/www/video/68_SM04.mov">Video 4</a></p>
<p>This work has been reported by <a href="http://newsoffice.mit.edu/2014/material-changes-color-texture-octopus-0916">MIT Featured News</a>, <a href="http://www.washingtonpost.com/news/speaking-of-science/wp/2014/09/16/camouflage-that-changes-color-and-texture-instantly-thanks-to-squid-skin/">The Washington Post</a>, <a href="http://online.wsj.com/articles/a-military-advance-with-the-aid-of-an-octopus-1411759180">Wall Street Journal</a>, <a href="http://www.slate.com/articles/video/video/2014/09/color_changing_camouflage_mit_research_could_let_soldiers_hide_like_an_octopus.html">The Slate</a>, <a href="http://www.gizmodo.com.au/2014/09/this-synthetic-material-changes-color-and-texture-like-octopus-skin/">Gizmodo</a>, <a href="https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.iflscience.com%2Ftechnology%2Ftwo-new-materials-mimic-octopus-camouflage&ei=2cQoVNb0IY6HyASLuILYDQ&usg=AFQjCNGKklFF_QSNqQAtOISmT2CNyXoZPg&sig2">IFLScience</a> and more</p>
<p>You may watch the video on Youtube: <a href="https://www.youtube.com/watch?v=kM-e2j8Equg">https://www.youtube.com/watch?v=kM-e2j8Equg</a> </p>
</div></div></div>Sat, 04 Oct 2014 16:53:59 +0000Qiming Wang17282 at https://imechanica.orghttps://imechanica.org/node/17282#commentshttps://imechanica.org/crss/node/17282Creasing-Wrinkling Transition in Elastomer Films under Electric Fields
https://imechanica.org/node/15795
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/5996">SAMs Lab research</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
<a href="http://www.duke.edu/~xz69/papers/55.pdf">Creasing-Wrinkling Transition in Elastomer Films under Electric Fields</a>
</p>
<p>
<a href="user/21855">Qiming Wang</a> and <a href="user/51">Xuanhe Zhao</a>
</p>
<p>
Creasing and wrinkling are different types of instabilities on material surfaces characterized by localized singular folds and continuously smooth undulation, respectively. While it is known that electric fields can induce both types of instabilities in elastomer films bonded on substrates, the relation and transition between the field-induced instabilities have not been analyzed or understood. We show that the surface energy, modulus and thickness of the elastomer determine the types, critical fields and wavelengths of the instabilities. By independently varying these parameters of elastomers under electric fields, our experiments demonstrate transitions between creases with short wavelengths and wrinkles with long wavelengths. We further develop a unified theoretical model that accounts for both creasing and wrinkling instabilities induced by electric fields and predicts their transitions. The experimental data agree well with the theoretical model.
</p>
<p>
E-mail: <a href="mailto:xz69@duke.edu">xz69@duke.edu</a>
</p>
</div></div></div>Sat, 14 Dec 2013 19:24:19 +0000Qiming Wang15795 at https://imechanica.orghttps://imechanica.org/node/15795#commentshttps://imechanica.org/crss/node/15795Phase Diagrams of Instabilities in Compressed Film-Substrate Systems
https://imechanica.org/node/15794
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/5996">SAMs Lab research</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
<a href="http://www.duke.edu/~xz69/papers/54.pdf">Phase Diagrams of Instabilities in Compressed Film-Substrate Systems</a>
</p>
<p>
<a href="user/21855">Qiming Wang</a> and <a href="user/51">Xuanhe Zhao</a>
</p>
<p>
Subject to a compressive membrane stress, an elastic film bonded on a substrate can become unstable, forming wrinkles, creases or delaminated buckles. Further increasing the compressive stress can induce advanced modes of instabilities including period-doubles, folds, localized ridges, delamination, and co-existent instabilities. While various instabilities in film-substrate systems under compression have been analyzed separately, a systematic and quantitative understanding of these instabilities is still elusive. Here we present a joint experimental and theoretical study to systematically explore the instabilities in elastic film-substrate systems under uniaxial compression. We use the Maxwell stability criterion to analyze the occurrence and evolution of instabilities analogous to phase transitions in thermodynamic systems. We show that the moduli of the film and the substrate, the film-substrate adhesion strength, the film thickness, and the pre-stretch in the substrate determine various modes of instabilities. Defects in the film-substrate system can facilitate it to overcome energy barriers during occurrence and evolution of instabilities. We provide a set of phase diagrams to predict both initial and advanced modes of instabilities in compressed film-substrate systems. The phase diagrams can be used to guide the design of film-substrate systems to achieve desired modes of instabilities.
</p>
<p>
E-mail address: <a href="mailto:xz69@duke.edu">xz69@duke.edu</a>
</p>
</div></div></div>Sat, 14 Dec 2013 19:18:08 +0000Qiming Wang15794 at https://imechanica.orghttps://imechanica.org/node/15794#commentshttps://imechanica.org/crss/node/15794Bioinspired Surfaces with Dynamic Topography for Active Control of Biofouling
https://imechanica.org/node/14009
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/5996">SAMs Lab research</a></div><div class="field-item odd"><a href="/taxonomy/term/8338">Electro-cratering instability</a></div><div class="field-item even"><a href="/taxonomy/term/8339">biofilm</a></div><div class="field-item odd"><a href="/taxonomy/term/8340">dynamic elastomers</a></div><div class="field-item even"><a href="/taxonomy/term/8341">pneumatic simulation</a></div><div class="field-item odd"><a href="/taxonomy/term/8342">adhesion strength</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Phanindhar Shivapooja†, <a href="user/21855">Qiming Wang</a>†, Beatriz Orihuela, Daniel Rittschof, and Gabriel P. López, <a href="user/51">Xuanhe Zhao</a>
</p>
<p>
† Equal contribution<br /><a href="mailto:gabriel.lopez@duke.edu"></a>
</p>
<p>
Fracture, debonding and instabilities have been commonly regarded as failure modes in engineering systems. Here, we show that the controlled deformation and instability of surfaces can induce effective detachments of various types of biofoulings through fracture and debonding of the fouling organisms. This new mechanism can potentially be used to address biofouling problems across many human endeavors including maritime operations, medicine, food industries, and biotechnology.
</p>
<p>
Advanced Materials, <a href="http://www.duke.edu/~xz69/papers/45.pdf">DOI: 10.1002/adma.201203374 (2013)</a>; <a href="http://people.duke.edu/~xz69/papers/45_s.pdf">Supporting Information</a>
</p>
</div></div></div>Sat, 12 Jan 2013 18:12:46 +0000Qiming Wang14009 at https://imechanica.orghttps://imechanica.org/node/14009#commentshttps://imechanica.org/crss/node/14009Electromechanical instabilities of thermoplastics: Theory and in situ observation
https://imechanica.org/node/13399
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/3534">pull-in instability</a></div><div class="field-item odd"><a href="/taxonomy/term/5996">SAMs Lab research</a></div><div class="field-item even"><a href="/taxonomy/term/8041">creasing-cratering instability</a></div><div class="field-item odd"><a href="/taxonomy/term/8042">dielectric polymers</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Electromechanical instabilities of thermoplastics: Theory and in situ observation
</p>
<p>
<a href="user/21855">Qiming Wang</a>, Xiaofan Niu, Qibing Pei, Michael Dickey, <a href="user/51">Xuanhe Zhao</a>*
</p>
<p>
Appl. Phys. Lett. 101, 141911 (2012); <a href="http://dx.doi.org/10.1063/1.4757867">http://dx.doi.org/10.1063/1.4757867</a>
</p>
<p>
Abstract: Thermoplastics under voltages are used in diverse applications ranging from insulating cables to organic capacitors. Electromechanical instabilities have been proposed as a mechanism that causes electrical breakdown of thermoplastics. However, existing experiments cannot provide direct observations of the instability process, and existing theories for the instabilities generally assume thermoplastics are mechanically unconstrained. Here, we report in situ observations of electromechanical instabilities in various thermoplastics. A theory is formulated for electromechanical instabilities of thermoplastics under different mechanical constraints. We find that the instabilities generally occur in thermoplastics when temperature is above their glass transition temperatures and electric field reaches a critical value. The critical electric field for the instabilities scales with square root of yield stress of the thermoplastic and depends on its Young’s modulus and hardening property.
</p>
<p>
PDF is available at <a href="http://www.duke.edu/~xz69/papers/44.pdf">http://www.duke.edu/~xz69/papers/44.pdf</a> <br />
*E-mail: <a href="mailto:xz69@duke.edu">xz69@duke.edu</a>
</p>
</div></div></div>Mon, 08 Oct 2012 15:13:34 +0000Qiming Wang13399 at https://imechanica.orghttps://imechanica.org/node/13399#commentshttps://imechanica.org/crss/node/13399Dynamic Electrostatic Lithography: Multiscale On-demand Patterning on Large-Area Curved Surfaces
https://imechanica.org/node/12118
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/5996">SAMs Lab research</a></div><div class="field-item odd"><a href="/taxonomy/term/7261">dynamic electrostatic lithography</a></div><div class="field-item even"><a href="/taxonomy/term/7262">multiscale on-demand patterning</a></div><div class="field-item odd"><a href="/taxonomy/term/7263">concave pattern</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
<a href="http://www.duke.edu/~xz69/papers/41.pdf"><strong>Dynamic Electrostatic Lithography: Multiscale On-demand Patterning on Large-Area Curved Surfaces</strong></a>
</p>
<p>
<a href="user/21855">Qiming Wang</a>, Mukarram Tahir, <a href="user/26248">Jianfeng Zang</a>, and <a href="/user/51">Xuanhe Zhao</a>*
</p>
<p>
<strong>Advanced Materials, In press </strong>
</p>
<p>
<em>Dynamic Electrostatic Lithography</em> is invented to dynamically generate various patterns on large-area and curved polymer surfaces under the control of electrical voltages. The shape of the pattern can be tuned from random creases and craters to aligned creases craters and lines, and the size of the pattern from millimeters to sub-micrometers.
</p>
<p>
*E-mail: <a href="mailto:xz69@duke.edu">xz69@duke.edu</a>
</p>
<p>
</p>
</div></div></div>Sat, 17 Mar 2012 16:09:29 +0000Qiming Wang12118 at https://imechanica.orghttps://imechanica.org/node/12118#commentshttps://imechanica.org/crss/node/12118Electro-creasing instability in deformed polymers: experiment and theory
https://imechanica.org/node/10372
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/882">electromechanical instability</a></div><div class="field-item odd"><a href="/taxonomy/term/3541">dielectrics</a></div><div class="field-item even"><a href="/taxonomy/term/5994">electro-creasing instability</a></div><div class="field-item odd"><a href="/taxonomy/term/5995">pattern formation</a></div><div class="field-item even"><a href="/taxonomy/term/5996">SAMs Lab research</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p align="center">
<strong><a href="http://www.duke.edu/~xz69/papers/35.pdf">Electro-creasing instability in deformed polymers: experiment and theory</a></strong>
</p>
<p align="center">
<span><a href="user/21855"><strong>Qiming Wang</strong></a>, Mukarram Tahir, Lin Zhang, and <a href="user/51"><strong>Xuanhe Zhao</strong></a>*</span>
</p>
<p><span><strong>Soft Matter, In Press</strong></span><span> </span><span> </span><span></span></p>
<p>
<strong>Abstract</strong>: Subjected to an electric field, a substrate-bonded polymer film develops a biaxial compressive stress parallel to the film. Once the electric field reaches a critical value, the initially flat surface of the polymer locally folds against itself to form a pattern of creases. We show that mechanical deformation of the polymer significantly affects the electro-creasing instability. Biaxially pre-stretching the polymer film before bonding to the substrate greatly increases the critical field for the instability, because the pre-stretch gives a biaxial tensile stress that counteracts the electric-field-induced compressive stress. We develop a theoretical model to predict the critical field by comparing the potential energy of the film at flat and creased states. The theoretical prediction matches consistently with the experimental results. The theory also explains why biaxially pre-stretching a dielectric-elastomer film greatly enhances the measured breakdown field of the film.</p>
<p><span>*</span><span> </span><span>To whom correspondence should be addressed. E-mail: <a href="mailto:xz69@duke.edu"><span><strong>xz69@duke.edu</strong></span></a></span>
</p>
<p></p>
</div></div></div>Mon, 06 Jun 2011 19:03:33 +0000Qiming Wang10372 at https://imechanica.orghttps://imechanica.org/node/10372#commentshttps://imechanica.org/crss/node/10372Creasing to cratering instability in polymers under ultrahigh electric fields
https://imechanica.org/node/9767
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/882">electromechanical instability</a></div><div class="field-item odd"><a href="/taxonomy/term/3541">dielectrics</a></div><div class="field-item even"><a href="/taxonomy/term/5994">electro-creasing instability</a></div><div class="field-item odd"><a href="/taxonomy/term/5995">pattern formation</a></div><div class="field-item even"><a href="/taxonomy/term/5996">SAMs Lab research</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p align="center">
<a href="http://www.duke.edu/~xz69/papers/34.pdf"><strong><span>Creasing to cratering instability in polymers under ultrahigh electric fields</span></strong> </a>
</p>
<p align="center">
<span><a href="user/21855">Qiming Wang</a>, <a href="user/23463">Lin Zhang</a>, and <a href="user/51">Xuanhe Zhao</a>*</span>
</p>
<p align="center">
<strong>Physical Review Letters, In press</strong>
</p>
<p><strong><span>Abstract: </span></strong><span>We report a new type of instability in a substrate-bonded elastic polymer subject to an ultrahigh electric field. Once the electric field reaches a critical value, the initially flat surface of the polymer locally folds against itself to form a pattern of creases.<span> </span>As the electric field further rises, the creases increase in size and decrease in density, and strikingly evolve into craters in the polymer. The critical field for the electro-creasing instability scales with the square root of the polymer’s modulus. Linear stability analysis overestimates the critical field for the electro-creasing instability. A theoretical model has been developed to predict the critical field by comparing the potential energies in the creased and flat states. The theoretical prediction matches consistently with the experimental results.</span><span> </span></p>
<p>
</p>
<p>
<span><span><strong><br /></strong></span></span><span>*</span><span> </span><span>To whom correspondence should be addressed. E-mail: <a href="mailto:xz69@duke.edu"><span>xz69@duke.edu</span></a></span>
</p>
<p>
<span><a href="http://www.duke.edu/~xz69/papers/34_s.pdf">Supporting information</a> ; </span><a href="http://www.duke.edu/~xz69/video/34_SM01.wmv">Video</a>
</p>
</div></div></div>Tue, 08 Feb 2011 17:52:28 +0000Qiming Wang9767 at https://imechanica.orghttps://imechanica.org/node/9767#commentshttps://imechanica.org/crss/node/9767Error | iMechanica