Thermodynamically consistent Reference Interaction Site Model theory of the tangent diatomic fluid

Thermodynamic and structural properties of the tangent diatomic fluid are studied in the framework provided by the Reference Interaction Site Model (RISM) theory, coupled with a Modified Hypernetted Chain closure. The enforcement of the internal thermodynamic consistency of the theory is described in detail. The results we obtain almost quantitatively agree with available or newly generated simulation data. We envisage the possibility to extend the consistent RISM formalism to generic, more realistic molecular fluids.Comment: Typeset with LaTeX, 6 pages, 3 figures (5 subfigures), 28 references, submitted to Chem. Phys. Let

Using structure-based organic chemistry online tutorials with automated correction for student practice and review

This article describes the development and implementation of an open-access organic chemistry question bank for online tutorials and assessments at University College Cork and Dublin Institute of Technology. SOCOT (structure-based organic chemistry online tutorials) may be used to supplement traditional small-group tutorials, thereby allowing students to develop essential problem-solving skills in organic chemistry. This online approach may be used for both formative and summative assessment. Students complete one problem set weekly or fortnightly, which consists of a number of questions of varying difficulty. A wide range of question types is possible; for example, prediction of reaction products, identification of reaction intermediates or reagents, and retrosynthetic analyses. Questions involving stereochemistry may be also be incorporated. The implementation is described, along with several sample questions and advice for creating questions. This approach is suitable for all levels of undergraduates, from introductory nonmajors to final-year chemistry students. Student feedback was overwhelmingly positive, and in particular, students found SOCOT to be a quite useful tool for review purposes. Our approach uses MarvinSketch, which is free for academic purposes, and the SMILES algorithm, which converts chemical structures into a text string and is compatible with any learning management system

Ninth and Tenth Order Virial Coefficients for Hard Spheres in D Dimensions

We evaluate the virial coefficients B_k for k<=10 for hard spheres in dimensions D=2,...,8. Virial coefficients with k even are found to be negative when D>=5. This provides strong evidence that the leading singularity for the virial series lies away from the positive real axis when D>=5. Further analysis provides evidence that negative virial coefficients will be seen for some k>10 for D=4, and there is a distinct possibility that negative virial coefficients will also eventually occur for D=3.Comment: 33 pages, 12 figure

Density functional studies of solvation forces in hard sphere polymer solutions confined between adsorbing walls. I. Solvent effects and dependence on surface potential range.

Solvation forces between large surfaces in athermal polymer solutions, in which both solvent particles and polymers are adsorbed at the surfaces, are studied with density functional theory. We investigate how the range of the surface potential affects the net interaction between the surfaces. Predictions from treatments in which the solvent is explicitly induced are compared with those obtained with more approximate models, where the solvent is either neglected, or enters the description implicitly. The results are interpreted via comparisons with simpler model systems. It is shown that a long-ranged surface potential, acting equally on monomers and solvent, leads to a solvent dominated repulsive solvation force, while polymer specific contributions dominate the net interactions when the adsorption potential has a short range. Effects of preferential polymer adsorption are also investigated. ©2003 American Institute of Physics

Density Functional Study of Surface Forces in Athermal Polymer Solutions with Addititve Hard Sphere Interactions. Solvent Effects, Capillary Condensation and Capillary-Induced Surface Transitions.

A density functional theory for polymer solutions is generalized to cases where the monomers have a different diameter to the solvent. An appropriate free energy functional is obtained by integration of the generalized Flory equation of state for such systems. This functional predicts that entropic demixing may occur in polymer solutions in which the solvent particles are smaller than the monomers. Demixing is promoted not only by a large size disparity, but also by a high pressure as well as by polymer length. The existence of two separate phases in the bulk solution suggests the possibility of capillary-induced phase transitions, even when the confining surfaces are hard, but otherwise inert. We examine such phase transitions and their relation to surface forces and colloidal stability. The density functional theory also predicts that under certain conditions, layering transitions will occur at hard and flat surfaces. A transition from a thin to a thick polymer-rich surface layer may take place as the separation between two surfaces is decreased, and we study the concomitant change on the surface force. Stable thick phases are predicted even at very large undersaturations, and they give rise to a profound increase of the range and strength of the surface force.We furthermore include comparisons with predictions from a model in which the solvent only enters the description implicitly. Responses of the surface forces to changes in monomer diameter, solvent diameter, polymer density, and chain length are investigated

Inconsistency of the density-functional theory of adsorption when using computer simulations

The authors compare predictions of a recent density-functional theory for adsorption of argon onto a solid-carbon-dioxide substrate with Monte Carlo simulations of exactly the same system. The basic predictions of the density-functional theory are shown to be qualitatively at variance with the simulation results. In particular, the simulations show predominantly monolayer adsorption, with a second layer forming at higher bulk densities. There is no sign of the thick structureless films predicted by the recent density-functional theory