J. Klein et al., DIRECT MEASUREMENT OF SHEAR FORCES BETWEEN POLYMER-BEARING SURFACES SLIDING PAST EACH OTHER, Macromolecular symposia, 98, 1995, pp. 1149-1158
We have used a recently developed surface force balance to measure, wi
th extreme sensitivity, both lateral and normal forces between interac
ting surfaces, for the case of simple liquids and particularly with su
rface-attached polymers. The presence of polymers on the surfaces redu
ces drastically the force required to maintain them in sliding motion,
under a given normal load, relative to the bare surface case. We beli
eve this is due to the long range steric repusion which can sustain a
large normal load while maintaining a very fluid interfacial layer. Th
e effect is much more marked for end-tethered chains in a good solvent
than for adsorbed chains in a theta-solvent. This is attributed to th
e different extents of interpenetration of the compressed polymer laye
rs.