On the Nature of Conformational Transition in Poly(ethylene glycol) Chains Grafted onto Phospholipid Monolayers

Abstract

This study was aimed at understanding the nature of conformational transition(s) that occur in poly(ethylene glycol) chains with molecular weight 5000 (PEG5000) grafted onto phospholipid monolayers. The study was performed with monolayers of PEG−phospholipid, DSPE−PEG5000, at the air/water interface and on solid substrates. Surface pressure and surface potential measurements together with ellipsometry and Brewster angle and atomic force microscopy were used to assess changes in the conformation and hydration of PEG5000 chains with increasing PEG grafting density. A comparative analysis of our experimental data suggests that neither the concept of the first-order pancake-to-brush conformational transition nor the model considering two subsequent transitions, namely, pancake-to-mushroom and mushroom-to-brush transitions, are adequate in describing conformational changes in the DSPE−PEG5000 monolayer at the air/water interface. At low grafting densities, PEG5000 chains did behave as grafted polymeric chains ...