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In this paper, a model for predicting adsorption of nonionic polymers from aqueous solutions to solid surfaces has been presented. The model is based on continuum form of the self-consistent mean field theory. The model incorporates the effect of the hydrogen bond using Flory-Huggins model with a concentration-dependent Flory-Huggins parameter. The self-consistent field is derived using the Evans and Needham approach. The model has been validated using the reported experimental data on adsorption of poly(ethylene oxide) (PEO) from aqueous solution to silica. All the parameters of the model have been estimated from the reported data of the independent experiments specifically directed to obtain these parameters. Thus, the concentration-dependent Flory-Huggins parameter is estimated from the water activity in PEO solution, Kuhn length through the radius of gyration of PEO under Θ conditions, and polymer-surface affinity parameter through the specific enthalpy of displacement of water by PEO in the limit of zero adsorption. The model quantitatively predicts the adsorbed amount in trains, loops, and tails and the hydrodynamic thickness of the adsorbed layer. It also correctly predicts the effect of pH and molecular weight of PEO on these quantities. The advantage of this approach is that it allows direct extension of models, describing thermodynamics of hydrogen bond in the bulk, to the interfacial region. The other important contribution of this work is that it shows that, for estimation of the adsorbed amount in the form of trains, the calorimetric technique yields results which are consistent with the NMR spin relaxation technique.

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.

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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.