Carl Peter Franck, PhD - US grants

This research program is to learn about the behavior of liquid mixtures near solid boundaries. The work is primarily experimental. The fundamental issues are the nature of the boundary states, including their microscopic structure; the role and origins of short and long range substrate-liquid interactions; the importance of thermal fluctuations; and the response to thermodynamic forces both in and out of equilibrium. There are three main projects: First, a capillary rise exploration of the transitions between states of wetting at bulk coexistence. The variables here are temperature and the chemistry of the bulk liquids and the substrates. Second, optical studies of the polarization and intensity of reflected light from liquid-solid interfaces as a means of uncovering microscopic features of equilibrium wetting layer structure. Third, the exploration of the nonequilibrium response of wetting structures to temperature changes with time and fluid motion. The aim here is to learn about otherwise inaccessible regimes of equilibrium response as well as time-dependent phenomena. As a supplementary project, they will join with the research group of Benjamin Widom to study the interfacial structure and energy of phase-separated polymer solutions through reflectivity and capillary rise experiments.

9320910 Franck Technical abstract: The equilibrium and dynamic properties of liquid mixtures, especially near boundaries will be investigated using ellipsometric techniques. A key feature of the experiments is the achievemenr of a very high temperature stability and very low thermal gradients. Studies include the following: uncovering new surface critical phenomena through chemical tuning, determining the effect of weak thermal convection on the delicate liquid structure necessary to achieve gravity thinned wetting in equilibrium, investigate potential of non equilibrium methods to when limited by long equilibration times in polymer solution studies, and search for correlated motion statistically in the dynamics of colloidal particles subject to intense thermal noise and slight long range intermolecular forces. Non-technical abstract: We have recently discovered details about how fluctuations in a thermal system behave near a boundary. Up to now the effect of the boundary has always been so great in microscopic observations that increasing its influence would not lead to any new information. The situation is like listening to a radio that is so loud that one can make out the rhythm of a song but not the words. A potential solution is to reduce the strength of the boundary through chemical means. Reflected light is used to detect changes at the surface. With accurate temperature control the sensitivity of amplifying the effect of thermal fluctuations is equal to the experimental precision of a few parts in a million. ***