Neutron reflectometry studies of polymer brushes in confined geometry subject to shear

ANYL 459

Gregory S. Smith, smithgs1@ornl.gov1, Tonya L. Kuhl, tlkuhl@ucdavis.edu2, William A Hamilton, hw5@ornl.gov1, Dennis Mulder2, and Sushil K. Satija, satija@nist.gov3. (1) HFIR Center for Neutron Scattering, Oak Ridge National Laboratory, PO Box 2008 MS 6393, Oak Ridge, TN 37831-6393, (2) Department of Chemical Engineering and Material Science, UC Davis, One Shields Ave, Davis, CA 95616, (3) Center for Neutron Research, NIST, 100 Bureau Dr. STOP 8562, Gaithersburg, MD 20854
Using neutron reflectivity and the newly developed Neutron Confinement Cell (NCC), we have directly quantified the density distribution of opposing polymer brushes confined between two parallel plates in good solvent conditions. With an average separation between the plates of approximately 1000 Angstroms, our measurements show that the density profile in the overlap region between opposing polymer brushes flattens consistent with predictions from molecular dynamics simulations. A significant increase in density at the anchoring surfaces due to compression of the brush layers is observed. This compression or collapse of the brushes in restricted geometries strongly suggests that high density brushes do not interpenetrate significantly in good solvent conditions. In addition, for the first time, we have measured the effects of an applied shear stress on the sample. We find that shear creates a totally new disentangled structure which surprisingly relaxes only after a span of a few weeks.
 

Preparing for the Bright Future of Neutron Scattering in the U.S.: State of the Art in Neutron-Based Analysis
8:30 AM-11:40 AM, Thursday, 1 September 2005 Washington DC Convention Center -- 155, Oral

Division of Analytical Chemistry

The 230th ACS National Meeting, in Washington, DC, Aug 28-Sept 1, 2005