Durian Group
Department of Physics and Astronomy
University of Pennsylvania
209 South 33rd Street
Philadelphia, PA 19104-6396

Back row (L-R): Klebert Feitosa, Adam Roth, Paulo Arratia, Benjamin Polak, Ted Brzinski, Kerstin Nordstrom, Raul D. Colon Moreno;
Front Row (L-R): Hiroaki Katsuragi, Doug Durian, Lynn Daniels, Adam Abate.

About Doug:

My general research interests are in the area of "soft" condensed matter physics: the structure, dynamics, and macroscopic behavior of a very broad and general class of materials that are typically noncrystalline and composed of macromolecules such as polymers, liquid crystals, surfactants, or biomolecules. This growing field complements solid state and statistical physics, and has considerable overlap with disciplines of chemistry, chemical engineering, materials science, and even biology. A common theme in soft condensed matter is that while the materials are disordered at the molecular scale and homogeneous at the macroscopic scale, they usually possess a certain amount of order at an intermediate, or mesoscopic, scale due to a delicate balance of interaction and thermal effects. The general goal is to determine this structure and its dynamics, how it arises, and how it influences the macroscopic behavior. This is obviously of great practical interest, since almost all matter we encounter in our everyday lives is a form of soft condensed matter. This is also of great fundamental interest since while we understand the physics controlling the behavior of individual atoms and molecules, and the physics controlling the behavior of macroscopic chunks of matter, we are relatively ignorant of the complex connection between these well known limits and completely new and unexpected behavior often arise.

Since the mesoscopic structure of many forms of soft condensed matter strongly scatters visible light, they appear opaque. My current research takes advantage of this multiple light scattering property for noninvasive study of opaque materials such as foams, emulsions, colloidal suspensions, granular media, and biological tissues that are inaccessible to traditional measurement techniques. From the average intensity of diffusely transmitted light we can monitor details of the mesoscopic structure, while from fluctuations in the transmitted intensity we can monitor motion within the structure itself. As applied to foams, for example, we can now address stability issues directly in terms of the evolution of the structure formed by the dense random packing of gas bubbles. We can also address the unusual mechanical properties of foams, namely how they can support shear stress like a solid but also flow and deform arbitrarily like a liquid, directly in terms of the deformation and random stick-slip hopping of local clusters of bubbles from one tightly packed configuration to another. Since a great deal is already known about the atomic structure of liquids and soap films, but not about how soap bubbles aggregate to form a chunk of condensed matter, this work will provide the missing link to a fundamental understanding of foams in terms of their structure at length scales ranging from atomic all the way up to the macroscopic..