ES 240 project: Numerical Modeling of High Aspect Ratio Rod Arrays Responding to Various Stimuli

(i)      Describe the project:  High-aspect ratio rod arrays are interesting systems which can be responsive to various stimuli such as capillary force, heat, magnetic field, etc. In the literature, there is a study, which discusses pattern formation during wetting of Si nanorod arrays and calculated the lateral force for different displacement by finite element analysis. For this study, the stiffness of the material was fixed. So, the mechanical property of the rod could not be easily adjusted for more pronounced responses. Recently, there is a study, which reported fabrication of stiffness-tunable rods arrays by soft-lithography.  In my project, based on the tunable rod array systems, I would like to investigate:

-   the effects of different stiffness

-   the effects of surface morphology (scalloped vs flat cylinder)

on the responses of rod arrays to stimuli by finite element analysis.

When we consider the effects of stiffness of the rod, we may expect that the lower the stiffness, the more pronounced the response is. However, if the stiffness is too low, the rod can bend or collapse without other stimulus due to gravity. Thus, there is a lower limit of stiffness.  On the contrary, if the stiffness of the rod increases, there will be less response of rods if everything else is the same. However, depending on the magnitude of the force that we are interested in, there can be upper limits of stiffness. In this study, I will consider measurement data of different forces and explore how we can tune the system to sense the forces. In addition, another way of controlling required forces for observing response of rods is to modify the surface morphology. For rods of the same material and dimensions, I will study how the surface morphology changes the response of the rods and consider some parameters such as pitch and amplitude of scalloping for optimizing the effects.

 (ii)    Explain how FEM contributes to the project: I think FEM can be quite helpful for this project because it provides capability of investigating the effects of various parameters and complicate geometry.

 (iii) Reference:

J.-G. Fan, D. Dyer, G. Zhang and Y.-P. Zhao, “Nanocarpet Effect: Pattern Formation during the Wetting of Vertically Aligned Nanorod Arrays”, Nano Lett., 4, 2133-2138 (2004).

B Pokroy, A. Epstein, M. C. P. Gulda and J. Aizenberg, “Soft lithography for bioinspired nano-structured material: fabrication of echinoderm skin Fabrication of bio-inspired actuated nanostructures with arbitrary geometry and stiffness”, Adv. Mater. DOI 10.1021/adma.200801432, in press.