We apply statistical mechanical principles to derive simple expressions relating the hydrogen bond thermodynamic properties to the static dielectric constant of water. The approach followed by us was to develop an expression for the Kirkwood’s structure factor (g) of water, taking into account the dipolar correlations between a central molecule and H-bonded neighbors present in infinite number of shells surrounding the central molecule. The number of H-bonded neighbors in a specific shell was related to the probability P for the various donor/acceptor sites of any given water molecule to be associated. Neglecting cooperativity effects, we evaluated P by focusing only on the correct counting of H-bonds formed between various association sites rather than on the oligomer distribution. The theory yielded an extremely simple expression for the structure factor (g) of the fluid at any given temperature in terms of the enthalpy (H) and entropy (S) changes associated with bond formation. The proposed theory was then combined with the Kirkwood–Frohlich theory for evaluating the dielectric constant (ε0). We have demonstrated that the theory correctly predicts the dielectric constant of ice-I without the use of any adjustable parameters. We have then deduced estimates for H-bond thermodynamic properties (H=−5.58 kcal/mole of H-bonds; S=−8.89 cal/deg⋅mole of H-bonds) by fitting the theoretical results for ε0 of liquid water to available experimental data over temperatures ranging from 0 °C to the critical point of water. The error in the theoretical values was found to be within 1% of the corresponding experimental values over the entire range of temperatures studied. To further test the theory, we have demonstrated that the temperature variation of the average number of H-bonds per water molecule, calculated using the proposed theory with the above mentioned values for H and S, compares quite well with those estimated from various available spectroscopic and molecular simulation studies.

We present important new results from light-microscopy and rheometry on a moderately concentrated lyotropic smectic, with and without particulate additives. Shear-treatment aligns the phase rapidly, except for a striking network of oily-streak defects, which anneals out much more slowly. If spherical particles several microns in diameter are dispersed in the lamellar medium, part of the defect network persists under shear-treatment, its nodes anchored on the particles. The sample as prepared has substantial storage and loss moduli, both of which decrease steadily under shear-treatment. Adding particles enhances the moduli and retards their decay under shear. The data for the frequency-dependent storage modulus after various durations of sheartreatment can be scaled to collapse onto a single curve. The elasticity and dissipation in these samples thus arises mainly from the defect network, not directly from the smectic elasticity and hydrodynamics.

The effect of an electric field on the coalescence of two water drops suspended in an insulating oil is investigated. We report four new results. (i) The cone angle for the non-coalescence of drops can be significantly smaller (as small as $19^{\circ }$) than the value of $30.8^{\circ }$ reported by Bird et al. (Phys. Rev. Lett., vol. 103 (16), 2009, 164502). (ii) A surprising observation of the dependence of the mode of coalescence/non-coalescence on the type of insulating oil is seen. A cone–cone mode for silicone oil is observed as against cone–dimple mode for castor oil. (iii) The critical capillary number for non-coalescence decreases with increase in the conductivity of the droplet phase. (iv) Systematic experiments prove that the apparent bridge during non-coalescence is indeed transitory and not permanent, as reported elsewhere. Theoretical calculations using analytical theory and the boundary integral method explain the formation of the cone–dimple mode as well as the transitory bridge length. The numerical calculation and thereby the physical mechanism to explain the occurrence of very small non-coalescence angles as well as the dependence of the phenomenon on the conductivity of the insulating oil and the water droplets remain unexplained.

Kinetics of oxidation of chloride ion is studied on both active platinum electrode and that undergoing transient passivation. Experiments are conducted in concentrated NaCl solution at rotating disk electrode. It is observed that on the active platinum electrode, oxidation is very fast, and hence the current density is controlled by the ohmic resistance of the solution. Electrode kinetics becomes important only when the electrode is passivated to a significant extent. Kinetics of chloride oxidation on the electrode undergoing passivation is modeled using the ButlerÀVolmer equation, in which the contribution from the ohmic resistance of the solution is incorporated. Two regimes of passivation are identified. The first is the fast regime corresponding to the formation of the platinum oxide monolayer. In this regime, the rate of passivation is first order in the concentration of the metal sites on the surface. In the slow passivation regime, the exchange current density for chloride oxidation is found to vary inversely with square root of time. This regime is modeled by considering unsteady diffusion of oxygen ions through the metal lattice. From this analysis it is concluded that the chloride oxidation current is almost totally contributed by a small fraction of the active metal sites which are continuously being regenerated as a result of diffusion of oxygen ions from the surface into the bulk of the metal.

We apply principles of statistical mechanics to derive simple expressions relating the hydrogen bond thermodynamic properties to the static dielectric constant of aqueous solutions. The approach followed by us was to develop an expression for the dipolar correlations between a centrally fixed molecule of a given type and its neighbors present in the surrounding shells, in terms of bonding probabilities, and combine the resulting expression with the Kirkwood–Frohlich equation. We considered only those neighboring molecules which are a part of the H-bonded cluster containing the central molecule. The bonding probabilities were evaluated by assuming a reaction equilibrium model, in which the formation of clusters between different association sites was represented by a series of chemical reactions. To demonstrate the utility of the theory, we provide comparison of the results for the temperature and composition variation of dielectric constant and H-bond stoichiometry of three model systems, methanol+water, ethanol+water, and acetone+water mixtures, against available experimental/simulation data.

A continuum version of self-consistent field model for polymer adsorption at the solidliquid interface has been formulated and solved to obtain configurational statistics of an adsorbed polymer chain. The solid surface is viewed as a singular phase (having zero thickness but finite adsorption capacity) in equilibrium with the solution. Chain configuration is described by the random flight model. The surface boundary condition accounts for both the configurational constraint and the adsorption equilibrium. The potential field is described by a modified form of the Flory-Huggins theory, which incorporates the effect of unequal partial volumes of the species (chain segment and solvent molecule) in the solution and their unequal partial areas in the surface phase. The model predictions are in qualitative agreement with the Scheutjens and Fleer model, except that the model predicts a negative value of c / , the critical adsorption energy parameter. The model has been validated using experimental data reported in the literature.The present model has advantages over the Scheutjens and Fleer model both in terms of ease of computation and the ability of the model to account for the difference in the packing densities between the solution and the surface.

In the petroleum industry, dehydration and desalting of a crude oil−brine emulsion are critical to further processing and refining of crude. The process of dehydration and desalting is typically done in large units called electrocoalescers. Enhancing the performance of an electrocoalescer includes the ability to dehydrate the emulsion in a shorter time, that is to increase the rate of separation of water while keeping the operation safe. The work proposes the enhancement of separation based on AC electric field modulation. The modulated waveform is composed of a high amplitude electric field step, followed by a low amplitude electric field step, and the process is repeated. The work demonstrates the efficacy of the technique through several experiments and their analysis. The work includes designing and optimizing the electrical waveform and then demonstrating the faster kinetics of electrocoalescence achieved in comparison with the conventional practice. The main advantage of modulation is facilitation of chaining of drops during the high voltage period, followed by their effective coalescence in the low voltage period. The effect of the modulation field and period has been investigated, and optimization of the time periods of the high field and the low field steps is carried out. Our analysis indicates that an increase in the fraction of the total period spanned by the high field improves the water separation, while a relatively weaker dependence is found on the total period. The electric field was applied both in directions parallel and perpendicular to the gravity, and performances were compared. It was found that the parallel configuration was better than the perpendicular configuration.

We report novel observations revealing the catastrophic breakup of water drops containing surfactant molecules, which are suspended in oil and subjected to an electric field of strength approximately 10(5) V/m. The observed breakup was distinctly different from the gradual end pinch-off or tip-streaming modes reported earlier in the literature. There was no observable characteristic deformation of the drop prior to breakup. The time scales involved in the breakup and the resultant droplet sizes were much smaller in the phenomenon observed by us. We hypothesize that this mode of drop breakup is obtained by the combined effect of an external electric field that imposes tensile stresses on the surface of the drop, and characteristic stress-strain behavior for tensile deformation exhibited by the liquid drop in the presence of a suitable surfactant, which not only lowers the interfacial tension (and hence the cohesive strength) of the drop but also simultaneously renders the interface nonductile or brittle at high enough concentration. We have identified the relevant thermodynamic parameter, viz., the sum of interfacial tension, sigma, and the Gibbs elasticity, epsilon, which plays a decisive role in determining the mode of drop breakup. The parameter (epsilon + sigma) represents the internal restoration stress of a liquid drop opposing rapid, short-time-scale perturbations or local deformations in the drop shape under the influence of external impulses or stresses. A thermodynamic "state" diagram of (epsilon + sigma) versus interfacial area per surfactant molecule adsorbed at the drop interface shows a "maximum" at a critical transition concentration (ctc). Below this concentration of the surfactant, the drop undergoes tip streaming or pinch off. Above this concentration, the drop may undergo catastrophic disintegration if the external stress is high enough to overcome the ultimate cohesive strength of the drop's interface.