Understanding and Exploiting T_g Reduction for Surface and Bulk Modification of Polymers with CO_2

摘要

In addition to the well-known reduction of bulk T_g by CO_2, we have investigated the existence of a reduced T_g for the surface layer of a polymer, and evaluated the effects of CO_2 on this transition and the corresponding layer thickness. The ability to control the depth of the rubbery layer of a polymer affords even greater control over the impregnation process. We will present our current understanding of the fundamental basis for this behavior and a theoretical analysis centered on a description of the entropy density of the surface layer. Subsequently this phenomenon will be the framework for discussing several derivative applications including: modification of biomedical implants for controlled release of therapeutics, bulk extrusion of thermally labile drug compounds with pharmaceutical polymers, and bonding of polymer devices with nanoscale features.