Pressure Effects on Thermodynamics of Polymer Containing Systems

Abstract

The role of pressure on the phase diagram of polymer liquids and also polymer mixtures has been intensely studied in the past decades, and there has been increased interest in the effects of pressure on the miscibility of polymers(An et al. 1997; An & wolf, 1998; Blaum & Wolf, 1976; Geerissen et al. 1985; Hammouda & Bauer, 1995; Hosokawa et al. 1993; Lefebvre et al. 2000; Maderek et al. 1983; Rabeony et al. 1998; Wolf & Blaum, 1976, 1977; Wolf & Jend, 1977,1978). One reason is the need for such data to more fully understand polymer miscibility in relation to the various proposed theories and equations of state. Another is the realization that such pressure effects could be important in many situations where such blends are used, e.g., when mixing a blend in an extruder or in forming articles from a blend by injection molding. These needs have led to the development of pressure cells that can be used with both light and neutron scattering such that the phase behavior and interaction strengths of blends can be measured. In past work, a wide range of phase behavior at chosen composition or near critical point of polymer solutions and polymer blends was found(Beiner et al. 1998, 2002; Blaum & Wolf, 1976; Hammouda et al. 1997; Janssen et al. 1993; Lefebvre etal 1999; Schwahn et al. 2001; Wolf & Blaum, 1977; Wolf & Jend, 1977; Zeman P Zeman et al. 1972). There are also many works on the theories about the pressure effects on the thermodynamics of polymer liquid and blends(An et al. 1997; An & wolf, 1998; Dudowicz & Freed, 1995, 2006; Kumar, 2000; Patterson & Robard, 1978; Walsh & Rostami, 1985). As several outstanding problems remain unexplained in these blends, we decided to investigate the dependence on pressure, an independent thermodynamic variable. The phase behavior of polymer liquids is commonly described in the terms of the lattice model of Flory and Huggins (FH), and the thermodynamics of typical polymer containing systems are understood in the framework of the incompressible random phase approximation. According to original FH theory, the rigorous incompressible system should be unaffected by pressure. In contrast to rigid lattice theories, equation-of-state (EOS) theories are capable of predicting the thermodynamics of polymer containing systems.