Insight into phase behavior and microstructure of complex fluids

Walter Chapman, Rice University

To design and optimize processes and products in the energy, chemicals, and materials industries, engineers need computational tools to predict bulk and interfacial equilibrium properties for complex fluids in terms of temperature, pressure, composition, and molecular geometry.  Systems that have been particularly challenging to model include associating or polar molecules as well as polymers and amphiphiles.  Such molecules are important in a range of applications from flow assurance and enhanced oil recovery in the energy industry to paints and coatings to self-assembly of polymer / nanoparticle systems.  Advances in statistical mechanics have led to successful molecular models for bulk fluids such as the statistical associating fluid theory (SAFT).  SAFT enables engineers to predict the effects of molecular weight, polydispersity, polarity, association, and compressibility on the bulk phase behavior of mixtures containing solvents, monomers, and polymers.  Further extensions of this approach using density functional theory show great promise in modeling interfacial properties and molecular structure, including the behavior of fluids at hydrophilic and hydrophobic surfaces, segregation in polymer blends, self assembly of surfactants and block copolymers, and polymer depletion forces in polymer/colloid systems.

In this seminar, we briefly review the physical basis for the SAFT approach and the extension to interfacial systems.  An advantage of theoretically based models is that the theory can be systematically improved to address weaknesses or to extend the theory to more complex fluid systems.  Some recent extensions and applications of the SAFT approach for bulk and interfacial systems are presented.  These points are illustrated through comparisons with molecular simulation as well as phase equilibria data for monomers, solvents, and copolymer systems.