7 research outputs found
Resummed thermodynamic perturbation theory for bond cooperativity in associating fluids with small bond angles: Effects of steric hindrance and ring formation
In this paper we develop a thermodynamic perturbation theory for two site
associating fluids which exhibit bond cooperativity. We include both steric
hindrance and ring formation such that the equation of state is bond angle
dependent. Here the bond angle is the angle separating the centers of the two
association sites. As a test, new Monte Carlo simulations are performed, and
the theory is found to accurately predict the internal energy as well as the
distribution of associated clusters as a function of bond angle and bond
cooperativity.Comment: To appear in The Journal of Chemical Physic
Modeling micelle formation and interfacial properties with iSAFT classical density functional theory
Surfactants reduce the interfacial tension between phases, making them an important additive in a number of industrial and commercial applications from enhanced oil recovery to personal care products (e.g., shampoo and detergents). To help obtain a better understanding of the dependence of surfactant properties on molecular structure, a classical density functional theory, also known as interfacial statistical associating fluid theory, has been applied to study the effects of surfactant architecture on micelle formation and interfacial properties for model nonionic surfactant/water/oil systems. In this approach, hydrogen bonding is explicitly included. To minimize the free energy, the system minimizes interactions between hydrophobic components and hydrophilic components with water molecules hydrating the surfactant head group. The theory predicts micellar structure, effects of surfactant architecture on critical micelle concentration, aggregation number, and interfacial tension isotherm of surfactant/water systems in qualitative agreement with experimental data. Furthermore, this model is applied to study swollen micelles and reverse swollen micelles that are necessary to understand the formation of a middle-phase microemulsion
Understanding the Thermodynamics of Hydrogen Bonding in Alcohol-Containing Mixtures: Cross-Association
The
thermodynamics of hydrogen bonding in 1-alcohol + water binary mixtures
is studied using molecular dynamic (MD) simulation and the polar and
perturbed chain form of the statistical associating fluid theory (polar
PC-SAFT). The fraction of free monomers in pure saturated liquid water
is computed using both TIP4P/2005 and <i>i</i>AMOEBA simulation
water models. Results are compared to spectroscopic data available
in the literature as well as to polar PC-SAFT. Polar PC-SAFT models
hydrogen bonds using single bondable association sites representing
electron donors and electron acceptors. The distribution of hydrogen
bonds in pure alcohols is computed using the OPLS-AA force field.
Results are compared to Monte Carlo (MC) simulations available in
the literature as well as to polar PC-SAFT. The analysis shows that
hydrogen bonding in pure alcohols is best predicted using a two-site
model within the SAFT framework. On the other hand, molecular simulations
show that increasing the concentration of water in the mixture increases
the average number of hydrogen bonds formed by an alcohol molecule.
As a result, a transition in association scheme occurs at high water
concentrations where hydrogen bonding is better captured within the
SAFT framework using a three-site alcohol model. The knowledge gained
in understanding hydrogen bonding is applied to model vapor–liquid
equilibrium (VLE) and liquid–liquid equilibrium (LLE) of mixtures
using polar PC-SAFT. Predictions are in good agreement with experimental
data, establishing the predictive power of the equation of state