Session Cd - Interfacial & Thin-Film Instabilities.
ORAL session, Sunday, November 23
304, Moscone Center
Langmuir monolayers consist of amphiphilic molecules that are confined to the air-water interface and are intrinsically two-dimensional systems. In addition to isotropic gas and liquid phases, they are known to possess a large number of liquid crystal phases that are two-dimensional analogues of three dimensional smectic liquid crystals. The liquid crystal phases are composed of randomly oriented, mesoscopic domains and are known to exhibit anomalous viscous behavior(L. E. Copeland, W. D. Harkins, and G. E. Boyd, J. Chem. Phys. 10), 357 (1942).. However, the source of the anomalous viscosity is still not well understood. For example, is the measured viscosity due to the motion of molecules or the motion of domains? And if the later is the case, how does this mechanism depend on the microscopic structure? To explore these questions, we have built an apparatus to study mechanical and flow properties of Langmuir monolayers. It consists of a torsion pendulum to measure the shear modulus and the viscosity in a cylindrical geometry. The outer wall can be rotated to create a 2-d Couette flow. A Brewster angle microscope is used to directly observe domain motions, rearrangements, and extensions. We will present the results of simultaneous measurements of domain dynamics and viscoelastic coefficients.