Molecular conformation and mobility of polyamines adsorbed on silica studied by spin labeling

Poly(ethyleneimine) and poly(4-vinylpyridine) chains adsorbed on Nucleosil silica have been randomly labeled with nitroxide free radicals. The EPR sig nal is very sensitive to the molecular Brownian motion of the segments and shoves generally at least two different environments: trains adsorbed on th e surface with a restricted mobility, and loops and tails protruding into t he solution with a fast motion. The rotational correlation times and the re lative fraction of each population are given as functions of the coverage a chieved and of the specific surface area of the silica for the samples in c ontact with methanol and sometimes water. The overall picture is consistent with a diffuse layer for the PEI and a more compact one with some heteroge neities for the P4VP. (C) 1999 Academic Press.