Sorption and Diffusion of Small Molecules Using Transition-State Theory

• Published in: Simulation Methods for Polymers pp. 409 - 466
• Format: Book Chapter
• Language: English
• Published: United Kingdom CRC Press 2004; Taylor & Francis Group
• Subjects: Plastics & polymers technology; Polymer chemistry; Kinetic Monte Carlo Simulation; Small Molecule Diffusion; Transition State; Polymer Chain; Sorption Coefficient Distribution; Full Dimensionality; Polymer Method; Sorption Coefficient; Molecular Dynamics Simulations; KMC; Transition State Theory; Dividing Surface; Atactic Polypropylene; Penetrant Diffusion; Flexible Coordinates; Infinitely Stiff; Sorption State; Glassy Polymer; Potential Energy Gradient; Simulation Cell; Partition Function; Penetrant Molecule; Transition State Energy; Transition State Search; Generalized Coordinates
• ISBN: 0824702476; 9780824702472
• DOI: 10.1201/9780203021255-20

In numerous applications, it would be useful if molecular simulation could be used to predict how the solubility or diffusivity of a small molecule in a polymer film varied with respect to changes in the molecular architecture of the film, or with different film processing. For example, this ability would enable prescreening among the many possible chain structures that could be devised, so chemical synthesis efforts could be targeted towards the most promising candidates. Polymer materials for sorption-diffusion membranes are one of many fields in which such large synthetic efforts have been conducted [1-4]. However, two primary barriers prevent accurate predictions from becoming routine: (1) the absence of reliable potential energy functions for penetrantpolymer systems of interest, and (2) the need for methods that access the long time scales inherent in small-molecule diffusion. The development of potential energy functions is the subject of ongoing research. Efforts focus on general force fields applicable to wide classes of molecules [5-14] or to particular types of polymer chains [15-21]. (These are only some of many possible examples.) This chapter discusses small-molecule sorption and diffusion, with a focus on simulating penetrant diffusion through polymers over long time scales.