(450f) Interfacial Properties and Structure of Complex Fluids from Interfacial-Saft (Isaft) Density Functional Theory

Interfacial properties play an essential role in applications of great industrial importance, such as adhesion, polymer coating and thin films, paints, separations, catalysis, wettability and emulsions. This has motivated studies of complex macromolecular systems (hydrocarbons, proteins, polymers) in confined geometries, and at solid-fluid and fluid-fluid interfaces. As properties of complex chemical systems are being tailored at the nanoscale, a molecular level understanding of the interplay between interfacial properties, fluid structure, and macroscopic properties of the material is necessary. Experimental investigation of interfacial phenomena is hampered by the small scale of the systems. Molecular simulation provides an alternative to experimental techniques, but is computationally expensive, and thus often limited to short-chain molecules. Consequently, substantial efforts have been directed towards developing a theory for structure and thermodynamics of inhomogeneous polymeric solutions and blends

We have recently developed a new density functional theory (interfacial SAFT or iSAFT) to describe phase behavior and microstructure of mixtures of polymeric fluids in inhomogeneous environments. The theory is based on Wertheim's thermodynamic perturbation theory for association; it treats the polyatomic system as a mixture of strongly associating monomers. The theory has been found to accurately predict polymer depletion and surface-induced polymer segregation – key elements in applications of polymer-colloid systems and in coatings of polymer blends. The advantages of iSAFT over existing density functional theories include computational efficiency, accuracy of predicted molecular structure, and thermodynamic consistency between interfacial and bulk properties. In the bulk, the theory reduces to the successful SAFT equation of state. Further, unlike any other polymer density functional theory, this approach can explicitly include molecular association (hydrogen bonding) and the effect of hydrophilic and hydrophobic surfaces. In this work, we present new results obtained from iSAFT for polymer-colloid and polymer-nanoparticle systems. Furthermore, we take advantage of the fact that iSAFT can explicitly include molecular association to study the effect of solute size on the structure of water around a hydrophobic solute.