Classical density functional study of multisite amphiphile mesostructures

Density functional approach for modeling CO2 pressurized polymer thin films in equilibrium

We have used polymer density functional theory to analyze the equilibrium density profiles and interfacial properties of thin films of polymer in the presence of CO(2). Surface tension, surface excess adsorption of CO(2) on polymer surface, and width of the interface are discussed. We have shown the changes in these properties in the presence of CO(2) and with increasing film thickness and their inverse linear relationship with increasing chain length. One of our important findings is the evidence of segregation of end segments toward the interface. We have introduced a new method of representing this phenomenon by means of Delta profiles that show increase in segregation owing to the presence of CO(2) and with increasing chain length. We also make predictions for the octacosane-CO(2) binary system near the critical point of CO(2). Our results indicate qualitative trends that are comparable to the similar experimental and simulation studies.

Density-functional theory for complex fluids

Density-functional theory (DFT) and its variations provide a fruitful approach to the computational modeling of the microscopic structures and phase behavior of soft-condensed matter. The methodology takes deep root in quantum mechanics but shares a mathematical similarity with a number of classical approaches in statistical mechanics. This review discusses different strategies commonly used to formulate the free-energy functional of complex fluids for either phenomena-oriented applications or as a generic description of the thermodynamic nonideality owing to various components of intermolecular forces. We emphasize the connections among different schemes of DFT approximations, their underlying assumptions, and inherent limitations. We also address extensions of equilibrium DFT to phenomenological theories for the dynamic properties of complex fluids and for the kinetics of phase transitions. In addition, we highlight the recent literature concerning applications of DFT to diverse static and time-dependent phenomena in complex fluids.

Predicting the phases of a two-dimensional hard-rod system with real-space self-consistent field theory

Polymer self-consistent field theory numerical tools are applied to a two-dimensional hard-rod colloidal system. Rods are represented through an interaction site model density functional theory that is derived and expressed from a self-consistent field theory perspective. A weighted density approximation is used within the density functional theory, and the phase space is sampled without bias for any particular morphology. A completely ordered crystal phase is found as well as a liquid crystal state.

Interactions between nanocolloidal particles in polymer solutions: Effect of attractive interactions

We present a density-functional theory study of nanoparticle interactions in a concentrated polymer solution. The polymers are modeled as freely jointed tangent chains; all nonbonded interactions between polymer segments and nanoparticles are described by Lennard-Jones potentials. We test several recently proposed methods of treating attractive interactions within the density-functional theory framework by comparing theoretical results with recent simulation data. We find that the simple van der Waals approach provides the most accurate results for the polymer-mediated potential of mean force between two dilute nanoparticles. We employ this approach to study nanoparticle interactions as a function of nanoparticle-segment interaction strength and polymer solution density and temperature.

Density Functional Theory of Realistic Models of Polyethylene Liquids in Slit Pores: Comparison with Monte Carlo Simulations†

Density functional theory is applied to study properties of fully detailed, realistic models of polyethylene liquids near surfaces and compared to results from Monte Carlo simulations. When the direct correlation functions from polymer reference interaction site model (PRISM) theory are used as input, the theory somewhat underpredicts the density oscillations near the surface. However, good agreement with simulation is obtained with empirical scaling of the PRISM-predicted direct correlation functions. Effects of attractive interactions are treated using the random-phase approximation. The results of theoretical predictions for the attractive system are also in reasonable agreement with simulation results. In general, the theory performs best when the wall-polymer interaction strength is comparable to polymer-polymer interactions.

Classical density functional study of mixed amphiphile mesostructures

This paper presents a density functional study of mixed amphiphile solutions. The amphiphiles are modeled using four to seven fused hard spheres where the connectivity is such that the amphiphiles have a proper head group. We present calculations of lamellar and vesicle density distributions, paying particular attention to the morphology of the bilayer structures.

Interactions between colloidal particles in polymer solutions: A density functional theory study

We present a density functional theory study of colloidal interactions in a concentrated polymer solution. The colloids are modeled as hard spheres and polymers are modeled as freely jointed tangent hard sphere chains. Our theoretical results for the polymer-mediated mean force between two dilute colloids are compared with recent simulation data for this model. Theory is shown to be in good agreement with simulation. We compute the colloid-colloid potential of mean force and the second virial coefficient, and analyze the behavior of these quantities as a function of the polymer solution density, the polymer chain length, and the colloid/polymer bead size ratio.

Density functional theory for semiflexible and cyclic polyatomic fluids

The effects of bond angle and chain stiffness on the structures of semiflexible polyatomic fluids are investigated by incorporating the bending potential into a density functional theory [Y. X. Yu and J. Z. Wu, J. Chem. Phys. 117, 2368 (2002)] that combines a modified fundamental measure theory for the excluded-volume effects and the first-order thermodynamics perturbation theory for the chain connectivity. The refined density functional theory faithfully reproduces the density profiles and conformational properties of a variety of triatomic fluids near a hard wall in which extensive Monte Carlo simulation data are available. In particular, the theory is able to capture the structures of rigid cyclic trimers where all segments are identical. The variation of local density profiles with respect to the chain length of confined polyatomic fluids is also explored. For quadratomic fluids confined in slit pores, the density profile of the middle segments exhibits novel double peaks that are absent in a fully flexible chain model. In addition, the density functional theory is applied to predicting the conformational properties and adsorption behavior of heterogeneous triatomic fluids of type "ABB" mimicking surfactant molecules. The competition between surface adsorption and self-association of trimers consisting of surface active and self-binding "A" segments and neutral "B" segment is explored.