Studies of fluctuations on thin films of polymer melts
S.K.Sinha
U.California San Diego / Los Alamos Natl. Lab.
Studies of surface (capillary wave) fluctuations on polymer films using the techniques of x-ray scattering have yielded a number of intriguing results over the last few years and indicate that, unlike the surfaces of simple liquids, the dynamics of polymer surfaces and interfaces need to be understood in greater detail. In particular, issues such as interaction with the substrate, chain entanglement effects, and the approach to the glass transition all affect the dynamics at the surface. We shall discuss some recent results on fluctuations at the surfaces and interfaces of polystyrene films and bilayers of different thicknesses and at different temperatures obtained from studies of off-specular diffuse (static) scattering (which measures the static height-height correlation function) and also using the relatively new technique of X-Ray Photon Correlation Spectroscopy (XPCS) which is the analogue of Dynamical Light Scattering and measures the dynamical height-height correlation function. Both these techniques extend the lateral length-scales which can be probed to at least an order of magnitude smaller than those observable with light scattering.
We shall discuss to what extent these results can be described by the ordinary capillary wave theory for liquid surfaces and show that this breaks down for film thicknesses comparable to Rg..
Acknowledgements: Work done in collaboration with Hyunjung Kim (Sogang U., Korea), Zhang Jiang ( U.California San Diego), Larry Lurio and Xuesong Jiao (Northern Illinois U.), S.G.J. Mochrie ( Yale University), Adrian Ruhm ( MPI, Stuttgart), J.K.Basu(Indian Institute of Science,Bangalore), Jyotsana Lal (Argonne Natl. Lab.) and Miriam Rafailovich (SUNY Stony Brook)