HMC Physics Colloquium

Tuesdays at 16:30 in Shanahan Center for Teaching and Learning, Room B460

Sharon Gerbode

Harvard University

Squishy Physics: Probing Complex Materials and Visualizing Statistical Mechanics at the Particle Scale

Jan. 18, 2011

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. Exploring the fundamental principles that underlie this complexity, soft matter physics thrives at the intersection of physics with biology, chemistry and engineering, offering many new directions for interdisciplinary research.

In this talk, I will describe recent experiments on colloidal crystals composed of microscopic peanut-shaped dimer particles suspended in water. The Brownian particle motion introduces thermal fluctuations, driving crystallization into a periodic structure of densely packed particles. Unlike crystals of atoms, colloidal crystals can be directly visualized with an optical microscope, offering the unique opportunity to watch the time evolution of a thermodynamic system, particle by particle. In our studies of crystalline colloidal dimers, we "poke" the crystal by manipulating individual particles with optical tweezers. We find that the relaxation dynamics of the system back to its crystalline configuration is surprisingly slow and displays features that are typically associated with disordered glassy systems.