Wetting phenomena and nano forces

Wetting phenomena and nano force

Surface forces action in a vicinity of three phase contact line and other current problems in kinetics of wetting and spreading

The most important problem in kinetics of wetting and spreading from the author's point of view is a consideration of combined surface forces and capillary action in a vicinity of the apparent three phase contact line. The latter is equally important at the consideration of static or dynamics. Other current trends in kinetics of wetting and spreading are also briefly reviewed. It is impossible to cover the whole literature on the subject: it was around 5000 publications on that subject in 2009 only and the total number of publication in the area is 65,917 (according to Science Direct). The problems to be solved in the area are marked in italic bold and underlined

Wetting Phenomena and Nanoforces

Wetting phenomena and nano force

Foreword

Forewor

Effect of solvents on performance of polyethersulfone ultrafiltration membranes: investigation of metal ion separations

The new polyethersulfone (PES) based ultrafiltration membranes were formed using a two stage process of dry and wet phase inversion in non solvent coagulation bath. The effects of three different solvents such as, N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP) and Dimethyl sulphoxide (DMSO) of 82.5% and 85% concentrations on the performance of final membranes were extensively investigated. Scanning electron microscopy (SEM) image results proved that PES membranes with an asymmetric structure were successfully formed. The number of pores formed on the top layer of PES membranes using above-mentioned three solvents was the result of the combined effect of the thermodynamic properties of the system (composition, concentrations, and phase behaviour) and membrane formation kinetics, whereas, the formation of the macroporous sub layer of those membranes was controlled by the diffusion rate of solvent– nonsolvent. The flux of pure water, membrane resistance, mechanical stability, molecular weight cut-off (MWCO) and separation performance of the PES membranes were studied. Separation of metal ions from aqueous solutions was studied for Ni(II), Cu(II) and Cr(III) using two complexing polymer ligands: polyvinyl alcohol (PVA) and poly(diallyldimethylammonium chloride) (PDDA).The separation and permeate rate (flux) efficiencies of the new membranes are compared using different solvents and different PES/solvent compositions

Surface forces and wetting features in drops and capillaries

Using the DLVO (Derjaguin, Landau, Verwey, Overbeek) theory, which accounts for quantum mechanics and electrostatics at the macroscopic level, the thermodynamic expressions for (thermodynamic) equilibrium contact angles of drops on solid substrates and menisci in solid wall capillaries are, operationally and unambiguously, expressed in terms of the corresponding Derjaguin pressure. The latter’s S-shape is responsible for microdrops and other phenomena appearing on flat solid substrates

Hysteresis of the contact angle of a meniscus inside a capillary with smooth, homogeneous solid walls

A theory of contact angle hysteresis of a meniscus inside thin capillaries with smooth, homogeneous solid walls is developed in terms of surface forces (disjoining/ conjoining pressure isotherm) using a quasi-equilibrium approach. The disjoining /conjoining pressure isotherm includes electrostatic, intermolecular, and structural components. The values of the static receding θr, advancing θa , and equilibrium θe contact angles in thin capillaries were calculated on the basis of the shape of the disjoining/conjoining pressure isotherm. It was shown that both advancing and receding contact angles depend on the capillary radius. The suggested mechanism of the contact angle hysteresis has a direct experimental confirmation: the process of receding is accompanied by the formation of thick β-films on the capillary walls. The effect of the transition from partial to complete wetting in thin capillaries is predicted and analyzed. This effect takes place in very thin capillaries, when the receding contact angle decreases to zero

Aggregation in colloidal suspensions: Effect of colloidal forces and hydrodynamic interactions

The forces acting in colloidal suspensions and affecting their stability and aggregation kinetics are considered. The approximations used for these forces in numerical simulations and the importance of the balanced account for both colloidal forces and hydrodynamic interactions are discussed. As an example the results of direct numerical simulations of kinetics of aggregation either with account for hydrodynamic interaction between particles or without it are compared by varying the parameters of the interaction potential between particles and fraction of solid. Simulations are based on the Langevin equations with pairwise interaction between particles and take into account Brownian, hydrodynamic and colloidal forces. It is confirmed that the neglecting of hydrodynamic interaction results in an accelerated growth of aggregates. The results of numerical simulations of aggregation kinetics are compared with well known analytical solutions

Effect of aggregation on viscosity of colloidal suspension

This experimental study of viscosity of colloidal suspensions was performed using monodisperse polystyrene latex with particle diameter of 1.15 μm and a pH dependent negative zeta potential of up to 120 mV in aqueous solutions. The range of electrostatic repulsion between the particles was controlled by varying the concentration of potassium chloride. Suspensions under investigation were either in a stable, coagulated, or gelated, state depending on the salt concentration. Shear thinning behaviour was observed for all the samples studied. The dependence of viscosity on shear rate imposed was found to depend substantially on the salt concentration

Membrane-based point-of-use water treatment (PoUWT) system in emergency situations: a review

During emergency situations, effective and quick reactions are vital in order to supply safe and unpolluted drinking water within approved guidelines Point-of-use water treatment (PoUWT) system, for instance, portable membrane-based water treatment devices, could help affected people to survive while waiting for aids to arrive. In the context of portable membrane-based water purification devices, it is also found that the most literature does not mention particle depositions and interactions, and membrane fouling mechanisms that might occur in these devices. The latter is especially important if the device is for private use for certain type of contaminant. It is found that the information available in the literature is mostly based on the performance of devices in terms of the following: bacteria/viruses/particles removal, cost efficiency including maintenance and repair, capacity and flow rate of permeate and producing company. These are discussed briefly as well