Soft materials have a number of emergent properties that arise from the combination of geometry and softness, and encompass everyday materials such as the polymers, gels, powders, colloids, suspensions etc that are in us, on us and surround us. The study of these materials cuts across the traditional boundaries of solids, fluids and gases. Theoretical and experimental approaches to these problems at a macroscopic level use a combination of observational tools and ideas from continuum and statistical mechanics, and physical chemistry. We are interested in the simple properties of these complex materials with the goal of understanding their qualitative behaviors, manifest as their mechanical and transport properties, and their stability in the presence of external stimuli. We are also interested in harnessing these properties in such instances as adhesion mechanisms, locomotory designs, and various self-organized and self-assembled material systems. using experiments and theory to guide each other.
One theme is the dynamics of soft fluid-infiltrated gels, sponges and related entities. Using the theory of poroelasticity, we explained a number of anomalous experimental observations associated with the collapse of colloidal gels and provided a quantitative explanation for their failure via cracking and buckling. This led to a scaling theory for the dynamics of crack growth in fluid-infiltrated solids with applications to the dynamics of cracks in confined clay films, and explains the differential cooling-driven hexagonal patterns in geophysical formations such as Giant’s Causeway, with predictions that have been confirmed experimentally. We also proposed a new theory for the mechanics of cytoplasm as a poroelastic material, highlighting the role of water movements in various cell processes, that have been confirmed experimentally by our experimental collaborators.
A second theme involves understanding the role of fluid lubrication in soft systems, that lead to a general theory of lubrication at soft interfaces with relevance to cartilaginous joint lubrication, via a mechanism to generate a dynamical Reynolds bearing in soft systems with various different geometries and material combinations (elastic, poroelastic… ). We later generalized this theory to account for adhesion to understand how things become stuck, and also applied the theory to understand how carpets may fly close to a wall (motivated by the motion of skates, rays, and other rajimorphs), and recently realized experimentally by other groups.
A third theme is the mechanical behavior of ordered and disordered materials. Specific contributions include the experiments and theory for the stiffness of an ordered actin bundle, a combine experimental and theoretical study of disordered actin networks, and most recently a general theory for the mechanics of fragile random networks above and below the Maxwell isostatic critical point that uses geometric and topological ideas to derive scaling principles for the stiffness of the structures as a function of the coordination number. This has implications for a large range of soft materials such as foams, athermal polymer networks, cell biology, etc.
A recent example that links many of the themes of interest is a study of active agents, e.g. bristlebots, to mimic active matter such as cells, social insects, and flocking animals, using a combination of experiment, theory, and computation to show that it is possible to study swarming and the cooperative movement. A generalization of these ideas provides a physical basis for an evolutionary question of how sperm cooperate in a competitive environment.
Skotheim, J. and L. Mahadevan, Proceedings of the Royal Society of London (A) , 460, 1995-2020 (2004). [View PDF] [Download PDF]
C. N. Kaplan, N. Wu, S. Mandre, J.Aizenberg, and L. Mahadevan, Physics of Fluids 27, 092105, 2015. [DOI] [View PDF] [Download PDF]
C. N. Kaplan and L. Mahadevan, J. Fluid Mech . 781, R2 , 2015. [DOI] [View PDF] [Download PDF]