hydrogel

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 DukeSoft Active Materials Laboratorydirected by ProfXuanhe Zhaois 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 DukeOrthopaedic Bioengineering Laboratorydirected by Prof Farshid Guilak.

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

A previous worksuggested a critical condition to form surface creases in elastomers and gels. For elastomers, the critical condition seems to have closed a gap between experimental observations (e.g., by bending a rubber block) and the classical instability analysis by Biot. For gels, however, experiments have observed a wide range of critical swelling ratios, from around 2 to 3.7. Here we present alinear perturbation analysis for swollen hydrogels confined on a rigid substrate, which predicts critical swelling ratios in a similar range.

Many engineering devices and natural phenomena involve gels that swell under the constraint of hard materials. The constraint causes a field of stress in a gel, and often makes the swelling inhomogeneous even when the gel reaches a state of equilibrium. To analyze inhomogeneous swelling of a pH-sensitive gel, we implement a finite element method in the commercial software ABAQUS. The program is attached here. Contact Shenqiang Cai (shqcai@gmail.com) for a description of the program.

Inspired byrecent worksbyWei Hong,Xuanhe Zhao,Zhigang Suo, and their coworkers, we started a project on hydrogels, with particular interest in various instability patterns observed in experiments. The attachment is our first manuscript on this subject. Through this work we hope to achieve the following:

At the invitation ofDavid Clarkeon behalf of the UCSB/Los Alamos Institute of Multiscale Materials and Structures, I gave the following three lectures:

1. Large deformation and instability in dielectric elastomers
2. Large deformation and instability in swelling polymeric gels
3. Mechanics and electrochemistry of polyelectrolyte gels

The abstracts follow, and the slides are attached at the end of this post.

I'm attaching slides of a talk that I gave yesterday at the斯伦贝谢-Doll Research Center. In preparing the talk, I made liberal use of slides prepared byWei Hongfor his own presentations. The talk is mainly based on the following papers:

A polymer network can imbibe water from environment and swell to an equilibrium state. If the equilibrium is reached when the network is subject to external mechanical constraint, the deformation of the network is typically anisotropic, and the concentration of water inhomogeneous. Such an equilibrium state in a network constrained by a hard core is modeled here with a nonlinear differential equation. The presence of the hard core markedly reduces the concentration of water near the interface and causes high stresses.

Hydrogels have enormous potential for making adaptive structures in response to diverse stimuli. In a structure demonstrated recently, for example, nanoscale rods of silicon were embedded vertically in a swollen hydrogel, and the rods tilted by a large angle in response to a drying environment (Sidorenko, et al., Science 315, 487, 2007). Here we describe a model to show that this behavior corresponds to a bifurcation at a critical humidity, analogous to a phase transition of the second kind.

A large quantity of small molecules may migrate into a network of long polymers, causing the network to swell, forming an aggregate known as a polymeric gel. This paper formulates a theory of the coupled mass transport and large deformation.