hydrogel

Cavitation can be often observed in soft materials. Most previous studies were focused on cavitation in an elastomer, which is under different mechanical loadings. In this paper, we investigate cavitation in a constrained hydrogel induced by drying. With taking account of surface tension and chemo-mechanics of gels, we calculate the free energy of the system as a function of cavity size. The free energy landscape shows double-well structure, analogous to first-order phase transition.  Above the critical humidity, a cavity inside the gel is tiny.

Soft Matters, (2014) Advance article

The class started today.  I'll be teaching fracture mechanics this semester.  I'll be mostly using the class notes I wrote in 2010, but will post updated ones. 

In today's class I covered "Trouble with linear elastic theory of strength."  I have just posted updated notes of the lecture.  The new notes begin with the follwoing paragraphs.

Hydrogels that undergo a volume phase transition in response to an
external stimulus are of great interest because of their possible use as
actuator materials. The performance of an actuator material is normally
characterized by its force–stroke curve, but little is known about the
force–stroke behavior of hydrogels. We use the theory of the ideal
elastomeric gel to predict the force–stroke curves of a
temperature-sensitive hydrogel and introduce an experimental method for
measuring the curve. The technique is applied to PNIPAm hydrogels with
low cross-link densities. The maximum force generated by the hydrogel
increases with increasing cross-link density, while the maximum stroke

Consisting of alternating swelling and nonswelling polymeric layers (SLs and NLs), lamellar gels are 1D photonic crystals with tunable optical properties.  The lamellar structure induces a constraint between the SLs and the NLs, resulting in an anisotropic swelling behavior coupled with deformation.

Dear Colleagues,

I wish to bring to you my recent work with my supervisor Hui-Hui Dai on "Some  Analytical Formulas for the Equilibrium States of a Swollen Hydrogel Shell". Below is the abstract and attached is the preprint of the article. I will very much appreciate your comments and suggestions.

The Duke Soft Active Materials Laboratory directed by Prof Xuanhe Zhao is seeking a highly motivated postdoctoral fellow to study mechanics of polymers and hydrogels with applications in tissue regenerations. The work will be carried out in close collaboration with the Duke Orthopaedic Bioengineering Laboratory directed by Prof Farshid Guilak.

This paper has been accepted for publication in Soft Matter. DOI: 10.1039/c0sm00335b.