Polymer-CO2 Interfaces In Equilibrium. A Density Functional Study

Supercritical CO2 has been established as a very promising polymer processing solvent in many experimental studies. However, theoretically these systems haven't been studied in great detail. This work is aimed at bridging the gap between theoretical and experimental knowledge through molecular level analysis of the system using polymer density functional theory (PDFT). This theory offers semi-quantitative information at lower computational costs as compared to computer simulation. The basic idea of PDFT is to express the free energy as a functional of spatially varying density distribution, from which equilibrium density distribution and other thermodynamic information can be derived. Using a PDFT model parameterized to represent the octacosane(C28)-CO2 mixture, we can make predictions for the properties of a polymer-CO2 binary system. Of particular interest to polymer processing applications are the properties like surface tension, surface adsorption and width of the interface. In this talk we will present a detailed account of the equilibrium behavior of octacosane near the critical region of CO2. We will show how density profiles of the different segments and other thermodynamic properties of the system are affected by the introduction of CO2, and how these change in the vicinity of its critical point. We will use these results to show how the behavior of real polymers can be predicted in the supercritical CO2 environment.