Session: 13-15-02: Mechanics of Soft Materials II

Paper Number: 164825

Statistical Mechanics of Light- and Field- Responsive Soft Materials 

Light- and electric field- responsive polymeric materials are important for emerging technologies in fields ranging from soft robotics to biomedical devices. However, engineering models of these materials are largely phenomenological, which inhibits systematic materials design. I will present our recent work on formulating statistical mechanical models that account for the coupling between light and electric fields to entropic polymer elasticity.

First, we study polymers with photo-responsive mesogens that show spontaneous deformation when illuminated, due to a trans-cis bending of the mesogens. Liquid crystal elastomers networks with photo-responsive mesogens show spontaneous deformation when illuminated, due to a trans-cis bending of the mesogens. We develop a statistical mechanical model of this process that exploits the separation of energy scales between entropic elasticity and photoswitching. The separation of scales allows for a perturbative expansion that enables closed-form evaluation of the free energy and population of activated mesogens. By calibrating a small set of physically-interpretable parameters, we find good agreement between the model predictions and our experimental measurements of photoswitching and shape evolution.

Second, we study the role of nonlocal electrical interactions in polymer chains. We develop a consistent non-perturbative model of electrical fields interacting with polymer chains, and show that the nonlocal nature of the dipolar self-interactions drives the collapse of a polymer chain above a critical field, providing a pathway to understand instabilities and failure mechanisms in polymer chains subjected to large electric fields. We find that a dielectric polymer chain, constrained at both ends, sharply collapses when exposed to a high electric field. The chain collapse is driven by nonlocal dipolar interactions and anisotropic polarization of monomers, a characteristic of real polymers that prior theories were unable to incorporate. Once collapsed, a large number of chain segments accumulate at the center, locally increasing the electric field and polarization by orders of magnitude. The chain collapse is sensitive to the orientation of the applied electric field and chain stretch. Our findings not only offer new ways for rapid actuation and sensing but also provide a pathway to discover the critical physics behind instabilities and electrical breakdown in dielectric polymers.

This is joint work with Pratik Khandagale, Carmel Majidi, Timothy Breitzman, Gal deBotton, Carlos Garcia Cervera, Mahnoush Babaei, Matthew Grasinger. We acknowledge funding support from National Science Foundation, Army Research Office, and Air Force Office of Scientific Research. 

These words are added to reach the ASME requirement of 400 words. These words are added to reach the ASME requirement of 400 words.

Presenting Author: Kaushik Dayal Carnegie Mellon University

Presenting Author Biography: https://sites.google.com/view/kaushik-dayal-research-group/home?authuser=0

Authors:

Kaushik Dayal Carnegie Mellon University