Overview

In introductory physics courses, we learn about an idealized frictionless world of rigid bodies and smooth surfaces. Yet the physics of everyday life is complex: soft, sticky, squishy, and often far from equilibrium. Nature has demonstrated repeatedly that harder does not necessarily mean stronger, from flexible blades of kelp that survive rough tidal shear stresses to sand dunes that withstand high winds while drifting across the desert. The unique combination of solid and liquid-like properties exhibited by such systems also arises in some manmade materials – classic everyday examples include paint, concrete, and toothpaste. However, further incorporation of soft matter into modern engineering requires a deeper understanding of these materials. Soft matter physics explores the fundamental physical principles that underlie the complexity of such systems and has opened up an exciting new class of questions with applications to industry, biology, and materials science.

Colloids

Colloidal suspensions are thermal systems consisting of solid Brownian particles suspended in a liquid solvent. The colloidal particles can be large – on the scale of one micron –  making them big and slow enough to observe with an optical microscope. As such, colloids offer a truly unique opportunity to actually watch the time evolution of a thermodynamic system, particle by particle. This unprecedented window into the configurations and dynamics of thermal particles has revealed an intimate view of both equilibrium and nonequilibrium phases formed by ensembles of colloidal particles. Results obtained from experiments on colloidal systems have been used to probe unanswered questions in analogous atomic or molecular systems whose constituents are made inaccessible by both size and speed.

Plant Biomechanics

Plants actuate complex motions that are often overlooked because of their slow speeds.  Charles Darwin was so fascinated by plants that he painstakingly measured their positions over hours and days to study their motions.  Modern time-lapse imaging simplifies such studies immensely and has opened up a new arena for investigating plant deformations.  Exciting recent studies in plant biomechanics have demonstrated that plants actuate motion by controlling water content within their complexly structured tissues – sometimes via passive hygroscopic swelling in response to ambient environmental changes .  Such passive mechanisms for generating motion suggest new engineering principles that could allow us to harness energy from environmental sources like daily humidity and temperature cycles.  This nascent field in soft matter physics has already provided inspiration for novel products such as Lotus-Effect^© and promises to offer numerous other new directions for technology and engineering applications.

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