Christopher G. Jesudason

ESTIMATION OF EXCESS MOLAR VOLUMES, THEORETICAL VISCOSITIES, AND ULTRASONIC SPEEDS OF BINARY LIQUID MIXTURES AT DIFFERENT TEMPERATURES

Excess molar volumes, , have been derived by using viscosity data for the binary mixtures of styrene (STY) with dimethylsulfoxide (DMSO), acetone (ACT), chlorobenzene (CB), and ethanol (EA) at different temperatures. From the literature data of viscosities, entropies, (ΔS*, and enthalpies, (ΔH*, of activation of viscous flow have been determined. Moreover, theoretical values of viscosities and ultrasonic speeds of the binary mixtures were calculated using different empirical relations and theories. The results were discussed in terms of deviations in experimentally and theoretically calculated values. The sign and magnitude of these parameters were found to be sensitive towards interactions prevailing in the studied systems. The predicted properties show good accuracy in comparison with the experimentally derived properties.

Conformational characteristics of single flexible polyelectrolyte chain

The behaviour of a flexible anionic chain of 150 univalent and negatively charged beads connected by a harmonic-like potential with each other in the presence of an equal number of positive and free counterions, is studied in molecular dynamics simulations with Langevin thermostat in a wide range of temperatures. Simulations were carried out for several values of the bending parameter, corresponding to fully flexible polyion, moderately and strongly stiff polyion as well as for the case when bend conformation is preferable to the straight one. We have found that in all cases three regimes can be distinguished, which can be characterized as “random coil”, observed at high temperatures; “extended conformation” observed at moderate temperatures (of the order of 1 in reduced units), and compact “globular conformation” attained at low temperatures. While the transition between high-temperature random and extended conformations is gradual, the transition from the extended coil to the globular state, taking place at a temperature of about 0.2 in reduced units, is of abrupt character resembling a phase transition.

A review of molecular interactions in organic binary mixtures

The intention of this review article is to review the knowledge about interactions in organic binary liquid mixtures. Molecular interactions in organic binary liquid mixtures are interesting due to their extensive use in many fields of solution chemistry. The thermodynamics of component molecules present in various systems interacting are particularly interesting because they display fantastic results. Studies of different organic liquid mixtures represent the different modes of interactions prevailing in the component molecules. The number of parameters required describing the properties of a given class of mixtures increases sharply with the number of segment types involved. In recent years, the theoretical and experimental investigations of interactions between unlike molecules have been conveniently carried out using excess thermodynamic functions. The properties of liquid mixtures depend on the forces between molecules and on the nature and volume of these molecules, and change with the composition of the mixtures. This change, in turn, is reflected in the thermodynamic properties of the mixtures. The influence of significant contributions of a chemical, physical and geometrical nature that change excess thermodynamic properties is considered and explained in detail.

Densities, Refractive Indices and Ultrasonic Speeds of N,N-dimethylformamide + Acetone Binary Mixtures at Different Temperatures

Experimental densities, ρ, refractive indices, n, and ultrasonic speeds, u, at various compositions and at various temperatures from (298.15 to 313.15) K for N,N-dimethylformamide + acetone binary mixtures were measured. From these results excess molar volumes (), deviations in refractive indices (Δn), isentropic compressibilities (Δks), partial molar volumes (), and partial molar compressibilities (), of acetone in N,N-dimethylformamide were calculated. All the excess and deviation functions were fitted to Redlich–Kister polynomial equation to determine the fitting coefficients and the standard deviations. The values of and Δks showed negative deviations, whereas excess Δn showed positive values over the entire range of concentrations and temperatures. The observed variations of these parameters, with concentration and temperature are discussed in terms of the intermolecular interactions and structural effects between the unlike molecules of the binary mixtures.

New μ-space stochastic equation for dynamical systems in Liouville form

Abstract By examining both the divergence of the velocity vector in standard orthogonal Cartesian coordinate Γ space of dimension ℝ2ptN for the reasonably general case of a Hamiltonian with (a) continuous partial derivatives to at least second order in its variables and with (b) additively separable momentum and space variables, it is shown that the corresponding Liouville equation for such a class of dynamical processes cannot describe non‐linear motion in general in the spaces considered, although hitherto it has been assumed to be applicable for all general motion in this broad class, which encompasses a major portion of physical representation. To extend the scope of dynamical system description for these classes, a new stochastic equation which is everywhere in principle discontinuous is developed for a general Hamiltonian which is a functional of the space and momentum variables, where the form of the new equation is strikingly similar to the Liouville equation which utilizes continuous functions and variables. In this development, the average trajectory of a system point is proved to be orthogonal to any constant energy surface consonant with the system energy at equilibrium, which is analogous to a similar result for the Liouville equation where no such averages are implied. For the general class of Hamiltonians considered, the celebrated Poincaré recurrence theorem does not obtain, strongly suggesting that ergodicity or quasiergodicity may hold, in accordance with the fundamental assumptions of at least equilibrium statistical mechanics, and the Birkhoff theorem would have to be appropriately recast. Due to the fortunate similarity of form to the Liouville equation, it is conjectured that the algebraic techniques developed for solving the Liouville equation may greatly simplify or aid in the development of methods that can be used to solve the present stochastic equation. This equation does not assume the presence of binary collision only, as required in the standard first‐order Boltzmann equation as derived from the Liouville equation, and is therefore suitable to describe dense systems, and functions as another equation for dynamical systems. A discussion of some other new and adapted proposals resembling the Liouville equation is presented. Some new macroscopic variational principles for non‐equilibrium thermodynamical systems are proposed, where one object for future work would be to relate the microscopic description given here with the macroscopic principles. All the standard conservation and dynamical laws of classical mechanics are observed in this work.

I. Time Reversibility Concepts, the Second Law and Irreversible Thermodynamics

Time reversibility concepts and transformations are first reviewed and difficulties with the standard formulations indicated. The kinetic equations which were constructed to exhibit reciprocity relations in their transition probabilities based on time reversal ideas are examined next and a first principle analysis shows that the standard forms are not in accord with the first principles. A thermodynamical theory based on the Kelvin‐Clausius‐Planck definition of entropy and a modified form of the Benofy and Quay postulate concerning conductive heat is developed and reciprocity and other relations are derived as an example of one possible alternative to the standard treatments with their indicated inconsistencies.

One-Particle Representation of Heat Conduction Described within the Scope of the Second Law

The Carnot cycle and its deduction of maximum conversion efficiency of heat inputted and outputted isothermally at different temperatures necessitated the construction of isothermal and adiabatic pathways within the cycle that were mechanically “reversible”, leading eventually to the Kelvin-Clausius development of the entropy function S with differential dS=dq/T such that ∮CdS=0 where the heat absorption occurs at the isothermal paths of the elementary Carnot cycle. Another required condition is that the heat transfer processes take place infinitely slowly and “reversibly”, implying that rates of transfer are not explicitly featured in the theory. The definition of ‘heat’ as that form of energy that is transferred as a result of a temperature difference suggests that the local mode of transfer of “heat” in the isothermal segments of the pathway implies a Fourier-like heat conduction mechanism which is apparently irreversible, leading to an increase in entropy of the combined reservoirs at either end of the conducting material, and which is deemed reversible mechanically. These paradoxes are circumvented here by first clarifying the terms used before modeling heat transfer as a thermodynamically reversible but mechanically irreversible process and applied to a one dimensional atomic lattice chain of interacting particles subjected to a temperature difference exemplifying Fourier heat conduction. The basis of a “recoverable trajectory” i.e. that which follows a zero entropy trajectory is identified. The Second Law is strictly maintained in this development. A corollary to this zero entropy trajectory is the generalization of the Zeroth law for steady state non-equilibrium systems with varying temperature, and thus to a statement about “equilibrium” in steady state non-thermostatic conditions. An energy transfer rate term is explicitly identified for each particle and agrees quantitatively (and independently) with the rate of heat absorbed at the reservoirs held at different temperatures and located at the two ends of the lattice chain in MD simulations, where all energy terms in the simulation refer to a single particle interacting with its neighbors. These results validate the theoretical model and provides the necessary boundary conditions (for instance with regard to temperature differentials and force fields) that thermodynamical variables must comply with to satisfy the conditions for a recoverable trajectory, and thus determines the solution of the differential and integral equations that are used to model these processes. These developments and results, if fully pursued would imply that not only can the Carnot cycle be viewed as describing a local process of energy-work conversion by a single interacting particle which feature rates of energy transfer and conversion not possible in the classical Carnot development, but that even irreversible local processes might be brought within the scope of this cycle, implying a unified treatment of thermodynamically (i) irreversible (ii) reversible (iii) isothermal and (iv) adiabatic processes by conflating the classically distinct concept of work and heat energy into a single particle interactional process. A resolution to the fundamental and long-standing conjecture of Benofy and Quay concerning the Fourier principle is one consequence of the analysis.

Clusters of Ge and O Atoms and the Raman Spectra of Vitreous GeO2

We have constructed the clusters of atoms of germanium and oxygen atoms by using the density‐functional theory. By optimizing the structures for the minimum energy of the Kohn‐Sham equation, we are able to calculate the bond lengths. We use the local density approximation to obtain the electronic binding energy for each cluster. We find the vibrational frequencies of each and every cluster and compare the calculated values with those measured from the Raman spectra of GeO2 glass. The glass involves clustering of atoms. Hence some of the calculated values match with those found in the experimental data. In this way, we find that Ge‐O2 (triangular), Ge‐O3 (pyramidal) and Ge‐O6 (pyramidal) clusters are present in the glassy state.

Prediction of viscosities and COSMO-RS analyses in binary mixtures of N,N-dimethylformamide with acetone

ABSTRACT Experimental viscosities, η, for pure N,N-dimethylformamide (DMF) and acetone (ACT) and their binary mixtures are measured over the whole composition range as a function of temperature between 298.15 and 313.15 K. The deviations in viscosity, ∆η, Gibbs free energy of activation ∆G, entropies ∆S*, enthalpies ∆H of activation of viscous flow have been calculated. The determination of excess molar volumes, VηE, was calculated from the experimental viscosities for the binary mixtures. The conductor-like screening model is applied to interpret the intermolecular forces. The σ-profile is computed for the N,N-DMF and ACT with conductor-like screening model for real solvents. The experimental results were found to be in good agreement with the theoretical predictions. Moreover, viscosity data were calculated from the theoretical equations of Grunberg and Nissan, Hind et al. and Wilke for the entire systems. All results obtained were averaged experimentally and theoretically in terms of average deviations.

A structural-feature-based computational approach for toxicity prediction of water-soluble arsenicals

We have used the density functional theory to make a toxicity prediction model of water-soluble arsenicals (WSA). The structures have been optimised for the minimum energy of the Schrödinger equation. In the present work, the usefulness of electrophilicity and charge transfer in predicting the toxicity of WSA, namely, monomethylarsenic acid (MMA) (III), dimethylarsenic acid (DMA) (III), arsenic acid, arsenous acid, MMA (V) and DMA (V), is assessed. It is demonstrated that the toxicity of arsenicals (both electron donors and acceptors) in gas and solution phases can be adequately explained in terms of electrophilicities. Amount of charge transfer between the WSA and the biosystem, simulated as nucleic acid (NA) bases and DNA base pairs, indicates the importance of charge transfer in experimental toxicity. Interaction of arsenicals with NA bases/selected base pairs is determined using Paars charge-transfer formula. The experimental toxicity (LD50) of arsenicals are taken as dependent variables and the energy (E) along with DFT-based descriptors, namely, electrophilicity index (ω) and charge transfer (ΔN), are taken as independent variables. Fairly good correlation is obtained showing the significance of the selected descriptors on arsenicals that act as electron donors or acceptors in the presence of bio-molecules. Raman micro-spectroscopy also showed its potential applications in the toxicology screening of chemicals and new biomaterials, with a range of cell types.