A perturbation density functional theory for the competition between inter and intramolecular association

Abstract

Using the framework of Wertheim's thermodynamic perturbation theory we develop the first density functional theory which accounts for intramolecular association in chain molecules. To test the theory new Monte Carlo simulations are performed at a fluid solid interface for a 4 segment chain which can both intra and intermolecularly associate. The theory and simulation results are found to be in excellent agreement. It is shown that the inclusion of intramolecular association can have profound effects on interfacial properties such as interfacial tension and the partition coefficient.

Molecular theory for the phase equilibria and cluster distribution of associating fluids with small bond angles

“…We will consider the general case in a future publication. Also, classical density functional theories (DFT) for associating fluids based on Wertheim's theory 17,[29][30][31][32][33] have proven to be a powerful tool for the description of associating fluids at interfaces. Extension of the current theory to inhomogeneous systems in the form of DFT could be used to study the effect of bond angle in inhomogeneous associating fluids.…”

A Monte Carlo density functional theory for the competition between inter and intramolecular association in inhomogeneous fluids

“…In this section, we define the molecular model and extend the DFT of Marshall et al 34 for intramolecularly associating chain molecules into a MCDFT form. In this work, we follow Ghonasgi and Chapman 17,18 and consider molecules which consist of a chain of m hard spherical segments of diameter σ bonded at hard sphere contact.…”

“…DFT has proven to be a powerful tool in the study of interfacial systems; [28][29][30] a small set of applications of DFT includes adsorption of chain molecules in slit pores, 31 effect of association on the polymer phase diagram, 11 phase behavior of polymer-colloid mixtures, 32 and orientations of rod coil molecules adsorbed at liquid interfaces. 33 Recently, Marshall et al 34 extended the approach of SJ to interfacial systems in the context of DFT by treating Wertheim's theory in inhomogeneous form. The theory was found to be in good agreement with simulation data for the case of a fluid of 4-mers with association sites on the first and last segments in a planar slit pore.…”

“…For the associating 4-mer, the competition between intra and intermolecular association results in interesting behavior at low density, where it was shown that interfacial tension went through a maximum as temperature was decreased. 34 Also, it was shown that neglecting intramolecular association resulted in a significant underprediction of association in the system (as compared to simulation where the chains could intramolecularly associate). Unfortunately, the theory is very computationally demanding and can only be applied to very short chain molecules.…”

“…It would be numerically impractical to apply the theory of Marshall et al 34 to chain molecules with more than 5 segments; for this reason we convert this DFT for intra/inter molecular associating chain molecules into the form of a MCDFT. This is a two step process, first the theory must be converted into a form based around a molecular density, and the converted theory must be written in the form of a MCDFT.…”