Physics (Internal)

Polymer Monolayer Dynamics at the air/water interface

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract:
Viscoelastic properties of monomolecular layers of polymers on the air/ water interface is probed principally by surface light scattering. The method is a non-invasive one that makes use of spontaneous capillary waves, induced by density fluctuations within liquids under thermal equilibrium. The capillary waves are also called ripplons, and they propagate with temporal damping. The interface is determined to be molecularly smooth but still dielectric permittivity difference between air and water is large enough to give rise to strong light scattering. Thus, the scattering amounts to a surface analog of Brillouin scattering in bulk liquid wherein spontaneously propagating phonons interact with light. Thus, the power spectra of scattered light from the interface provide the propagation rate and the damping coefficient. Analysis is based on the resonant mode-coupling of lateral and transverse waves that are recast into the lateral storage modulus and the corresponding loss modulus. By virtue of the two- dimensional character of the monolayers, many intriguing observations have been made with respect to amphiphilic properties and chain architecture of homopolymers and copolymers. Close connection and correspondence between the static properties of polymer monolayers and their rheological behavior are established.