Interfacial Structure of Phosphorylcholine Incorporated Biocompatible Polymer Films

Neutron reflectivity (NR) has been used to determine the structure of dry and swollen PC100B biocompatible phosphorylcholine (PC) polymer films coated on the optically flat silicon oxide surfaces. Deuterium labeling to the dodecyl chain of PC100B polymer was found to be effective at highlighting the interfacial structure of dry PC100B films while the swelling with D<INF>2</INF>O into the fully hydrogenated PC100B polymer produced sufficient isotopic contrast for revealing structural features within the swollen films. The main structural characteristics of the dry PC films were found to consist of alternate layers at the SiO<INF>2</INF>/polymer and polymer/air interfaces, indicating that thermal annealing promoted segregation of hydrophilic and hydrophobic moieties within the polymer. The thicknesses of these sublayers were between 10 and 30 Å, and the layering feature gradually became diminished into the middle film region which is characterized by a uniform scattering length density (SLD) determined by NR. It was further observed that the outer surfaces of the dry polymer films contained a significant fraction of hydrophobic moiety as a result of surface energy minimization during annealing, but upon swelling in water this structural feature was deteriorated by fragment motions and redistributions. In contrast to the greater structural variation on the outer film surface, swelling had relatively less effect on the internal layering structure at the SiO<INF>2</INF>/polymer interface due to the structural constraints imposed by silyl cross-linking and the hydrophobic barrier to water diffusion. The thickness of the middle part of uniform region increases with dry film thickness, but the alternate layering at the interfaces was largely unaffected. The increase in annealing temperature enhanced silyl cross-linking, resulting in the reduced equilibrium water content across the films and the slowdown of the rate of swelling.