Educational Background:

PhD, Cornell University, 1953 AB, Columbia University, 1949 DSc (hon), University of Chicago, 1991 DSc (hon), University of Utrecht, 1999

Awards:

• New York Academy of Sciences Boris Pregel Award in Chemical Physics • ACS Langmuir Award in Chemical Physics • ACS Hildebrand Award in Theoretical and Experimental Chemistry of Liquids • Carnegie-Mellon University Dickson Prize for Science • University of Wisconsin Hirschfelder Prize • Royal Netherlands Academy of Arts and Sciences Bakhuis Roozeboom Medal • University of Trondheim Onsager Medal • Boltzmann Medal of the IUPAP Commission on Statistical Physics, 1998 • ACS Award in Theoretical Chemistry, 1999 • National Academy of Sciences • American Philosophical Society • American Academy of Arts and Sciences Fellow • New York Academy of Sciences Fellow

Research Description:

Ours is a program of theoretical research on fluids with emphasis on their phase transitions and phase equilibria. This includes studies of the critical points of the phase transitions (those states in which the previously distinct phases become identical) and of the structure and tension of the interfaces between coexisting phases. In recent years we have studied phase equilibria in complex, structured fluids such as polymer solutions and microemulsions. The theoretical tools we use are those of thermodynamics and statistical mechanics.

Recent work has included studies of line tension?the tension of the line in which three phases meet?especially its behavior near the point at which an interfacial phase transition (the "wetting" transition) occurs, in which the three-phase line itself disappears and one phase is then spread as a film between the other two. A related quantity of interest is the tension of the boundary between two different, coexisting interfacial structures. One of these two surface phases anticipates and prepares for the formation of a third bulk phase?a wetting phase?in an important phenomenon known as prewetting or premelting. These are novel and unexpectedly challenging problems with implications for heterogeneous nucleation and the mechanism of melting.

Current work includes analysis of theoretical models of fluids at low-energy polymer surfaces, emphasizing the angle of fluid-solid contact and its dependence on the interfacial tensions. An important issue is the question of how nearly the contact angle on a given surface is determined by the liquid-vapor tension alone.

We study such models also to learn about fluctuations in the structure of interfaces and to answer related questions of interfacial stability. The fluctuations are observable in the low-angle scattering of X-rays or neutrons. We determine them from an analysis of the spectrum of the matrix of second derivatives of the free energy with respect to the local concentrations or densities. The calculations are similar to those in analogous quantum mechanical problems.

We have also been studying a model of the gel electrophoresis of DNA?the dynamics of charged polymer chains in an applied electric field in a medium with a high density of obstructions. Here the interest is in the dependence of the steady-state drift velocity (terminal velocity) of the chains on the chain length and the magnitude of the field and in the related chain-length dependence of the diffusion coefficient. We study these questions in the context of the theoretical model both by analytical methods and by computer simulation.

Selected Publications:

Kolomeisky, A.B. and Widom, B. A Simplified 'Ratchet' Model of Molecular Motors. J. Stat. Phys. 1998, 93, 633.

Structure and Tension of Interfaces. Mol. Phys. 1999, 96, 1019.

Lekkerkerker, H.N.W.; Widom, B. An Exactly Solvable Model for Depletion Phenomena. Physica A 2000, 285, 483.

Widom, B.; Bhimalapuram, P.; Koga, K. The Hydrophobic Effect. Phys. Chem. Chem. Phys (PCCP) 2003, 5, 3085.

Djikaev, Y.; Widom, B. Geometric View of the Thermodynamics of Adsorption at a Line of Three-Phase Contact. J. Chem. Phys. 2004, 121, 5602.