Mechanics of Soft Active Materials

At the invitation of David Clarke on 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.

Lectures at UCSB and sent live to Los Alamos: 

Soft materials can be made active in that they can greatly change shape and volume in response to diverse stimuli. For example, an elastomer may strain more than 100% under an electric field. As another example, a gel may imbibe solvent molecules to swell a thousand times its initial volume. These soft active materials have broad applications in drug delivery, tissue engineering, microfluidics, and the oil industry.

My group has recently started to study the mechanics of soft active materials. We attempt to formulate theories that address commonly asked questions. How do stress, electric field, and chemical potential interplay to cause large deformation? Why do abrupt changes, or instabilities, occur?

In this series of talks I'll outline the basic theories and several specific phenomena. The sub-titles of the two talks are

• Large deformation and instability in dielectric elastomers
• Mechanics and electrochemistry of polyelectrolyte gels

Departmental seminar: Large deformation and instability in swelling polymeric gels

Flexible, long polymeric molecules can covalently crosslink into a three-dimensional network. The resulting material, an elastomer, is capable of large and reversible deformation. When the network is brought in contact with a solvent, the network imbibes solvent molecules and swells, resulting in an aggregate known as a gel. The swelling is also reversible: when the environment dries, the solvent molecules in the gel migrate out and evaporate. Gels are used in diverse applications, including medical devices, actuators in microfluidics, and packers in oil wells. Mixtures of macromolecular networks and mobile molecules also constitute many tissues of plants and animals.

Swelling of a network can be markedly influenced by a mechanical load. When the network, the solvent, and the mechanical load equilibrate, the deformation in the gel is usually anisotropic and inhomogeneous. This talk describes a nonlinear field theory of gels, building upon the work initiated by Gibbs, Biot, and Flory. The gel can undergo large deformation of two modes. The first mode results from the fast process of local rearrangement of molecules, allowing the gel to change shape but not volume. The second mode results from the slow process of long-range migration of the small molecules, allowing the gel to change both shape and volume. The theory is illustrated with examples of swelling induced large deformation, contact, and bifurcation.

The second edition of these slides has been posted.