Abstract
Static and dynamic surface interactions in deionized water were studied between poly(ethylene glycol) (PEG) and an opposed layer of either the same PEG or a highly charged cationic polymer, quaternized polyvinylpyridine (QPVP). The PEG, molecular weight 5000 g mol-1, was end-attached to hydrophobized mica by hydrophobic-driven adsorption of the lipid portion (distearoyl-phosphatidylethanolamine) of PEG-lipid diblock copolymers. The QPVP homopolymer, 98% quaternized and molecular weight 39,000 g mol-1, was allowed to adsorb statistically onto mica. Within the scatter of the data the force−distance curves could be fit equally well by the Alexander-de Gennes expression for brush-brush interactions or by exponential decay (decay length 4 nm). However, at every film thickness, the shear modulus of the PEG-PEG interface was less than that of PEG-QPVP by an order of magnitude. When the layers were compressed strongly, they remained demonstrably fluid, even in the most strongly compressed state, in the sense that...
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