Web Release Date: October 19,
Solvent Dependent Friction Force Response of Polystyrene Brushes Prepared by Surface Initiated Polymerization
and
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, Department of Materials Science & Engineering, University of Florida, Gainesville, Florida 32611-6400, and Department of Chemistry, University of Houston, Houston, Texas 77204-5003
Received May 1, 2007
In Final Form: August 20, 2007
Abstract:
Polystyrene (PS) brushes were prepared on oxide passivated silicon by the surface initiated polymerization (SIP)
technique. From an AIBN-type free radical initiator, which was silanized and immobilized on silicon wafers, styrene
brushes were directly polymerized and grafted from the surface. The formation of the initiator monolayer and,
subsequently, the polymer brush on the surface were monitored by X-ray photoelectron spectroscopy (XPS) and
ellipsometry. Friction force measurements were performed by atomic force microscopy (AFM), using a 5 
m SiO2
colloidal sphere tip and under systematically varied solvent environments (nonpolar to polar), to demonstrate
the dependence of brush lubricity on solvation. The relative uptake of solvents in the PS brush was determined by
quartz crystal microbalance (QCM), and it correlates well with friction data. It is surmised that, in poor solvent
environments, the polymer brush exists in a collapsed conformation, giving rise to the higher observed friction
response.
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