Energy Landscape Approaches to Understanding Soft Glassy Materials

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

NONTECHNICAL ABSTRACT This award supports computer simulation and associated education aimed to help understand the mechanical properties of a class of materials that are viscoelastic, being neither entirely solid nor liquid, and which include soap foams, toothpaste, mayonnaise and living cells. Remarkably, these seemingly very different materials respond very similarly to being pulled or squeezed, and have largely defied deep understanding. This project builds upon a recent breakthrough that stems from thinking of the system as analogous to a particle rolling downhill on an abstract energy landscape. That is, the seemingly complicated motion of the individual bubbles in a foam, when projected into this abstract space, resembles the twists and turns of a river canyon. The PIs will seek to better understand the shape of the landscape that causes the 'river' to twist and turn as it does, to make new versions of the model that give rise to 'rivers' having different shapes and to add real-world detail to the model. Similar 'landscape' approaches have also been found to be useful in machine learning algorithms with many applications, suggesting that the algorithms we develop and our findings may find useful application outside the field of Materials Research. This project will train both graduate and undergraduate students in this important state of the art research area. TECHNICAL ABSTRACT This award supports theoretical and simulation research and education to understand soft glassy materials, a broad class of materials including foams, emulsions, pastes, slurries and even living cells, that share a common set of unusual viscoelastic properties whose physical origins remain deeply mysterious. It will build upon recent studies using a foam model that show that the unusual mechanics of soft glassy materials - power-law rheology, super-diffusive particle motion and avalanches - are due to fractal properties of the system?s path in configuration space. Specifically, it will extend the model to capture the effects of viscous damping and applied shear, produce models having configuration paths with different fractal dimensions as well as probe the fractal geometry of the energy landscape itself. The net result is the development of a suite of tools for the actuation of non-equilibrium systems to probe and understand the geometry of energy landscapes and its relation to material properties. More broadly, it appears that the behavior of many complex adaptive systems, including the cells in our bodies, may be determined by the minimization of some very complex energy or fitness landscape embedded in a high-dimensional space, whose in-depth study is only now becoming practical due to advances in computation. This interdisciplinary project will provide ample opportunity for graduate and undergraduate student training in the development of state of the art tools for studying such high-dimensional energy and fitness landscapes. The tools developed in this proposal will be disseminated openly, and we anticipate them finding utility outside of material science.