Dense, Highly Hydrated Polymer Brushes via Modified Atom-Transfer-Radical-Polymerization: Structure, Surface Interactions, and Frictional Dissipation

Abstract

The conditions for atom transfer radical polymerization (ATRP) of poly[2-(methacryloyloxy)ethyl phosphorylcholine] (pMPC) chains are modified to enable much more efficient growth of these poly zwitterionic chains from macroinitiator-coated mica substrates using the “grafting from” technique. In particular, we demonstrate directly that achieving a lower level of oxygen in the reaction mixtures through longer evacuation results in the creation of significantly denser and more extended pMPC brushes, with substantially improved interfacial properties both in pure water and in 0.2 M NaNO3 salt solution. Using a surface force balance combined with atomic force microscopy and X-ray photoelectron spectroscopy, we characterize these brushes and determine the normal and especially shear interactions between them. Normal force profiles reveal that the grafting density is independent of the brush molecular weight M, and that the swollen brush thickness L scales linearly with M. Moreover, shear force measurements indi...