Dilatational viscosity of dilute particle-laden fluid interface at different contact angles

We consider a solid spherical particle adsorbed at a flat interface between two immiscible fluids and having arbitrary contact angle at the triple contact line. We derive analytically the flow field corresponding to dilatational surface flow in the case of large ratio of dynamic shear viscosities of two fluids. Considering a dilute assembly of such particles we calculate numerically the dependence upon the contact angle of the effective surface dilatational viscosity particle-laden fluid interface. The effective surface dilatational viscosity is proportional to the size and surface concentration of particles and monotonically increases with the increase in protrusion of particles into the fluid with larger shear viscosity

Long range corrections in liquid-vapor interface simulations

Long range corrections (lrc) for the potential energy and for the force in planar liquid-vapor interface simulations are considered for spherically symmetric interactions. First, it is stated that for the Lennard-Jones (LJ) fluid the lrc for the energy Δu of Janeček [J. Phys. Chem. B 110, 6264 (2006)] is the same as that of Lotfi et al. [Mol. Simul. 5, 233 (1990)]. Second, we present the lrc for the force ΔF for any spherically symmetric interaction as a derivative of Δu plus a surface integral over the cut-off sphere by using the extended Leibniz rule of Flanders [Am. Math. Monthly 80, 615 (1973)]. This ΔF corrects the incomplete lrc Δ1F of Lotfi et al. and agrees with the result of Janeček obtained by direct averaging of the forces. Third, we show that the molecular dynamics (MD) results for the surface tension γ of the LJ fluid with size parameter σ obtained by Werth et al. [Physica A 392, 2359 (2013)] with the lrc ΔF of Janeček and a cut-off radius rc = 3σ agree with the results of Mecke et al. [J. Chem. Phys. 107, 9264 (1997)] obtained with the lrc Δ1F of Lotfi et al. and rc = 6.5σ within −0.4% to +1.6%. Moreover, using only the MD results for γ of Werth et al., we obtain for the LJ fluid a new surface tension correlation which also represents the γ-values of Mecke et al. within ±0.7%. The critical temperature resulting from the correlation is Tc = 1.317 66 and is in very good agreement with Tc,ref = 1.32 of the reference equation of state for the LJ fluid given by Thol et al. [J. Phys. Chem. Ref. Data 45, 023101 (2016)]

The spectra of molecular light scattering in high-viscosity glycerol-like liquids

The mechanisms of formation of fine structures in the spectra of the polarized and depolarized components of molecular light scattering in high-viscosity liquids are studied. The temperature dependences of spectral parameters are examined. The results are treated in terms of the concept of a microheterogeneous structure of supercooled high-viscosity liquids

Novel food grade dispersants : review of recent progress

Many foreseen advances in the design of food structures, suitable for ever demanding nutrient delivery systems, tailored controlled release, microencapsulation and protection of active ingredients, require a generation of superior dispersants than those currently provided by proteins. While the most efficient structure for such dispersants is relatively easy to specify, in foods they cannot simply be synthetically manufactured. The review highlights several possible strategies for realising more efficient food colloid stabilisers and summarises the key recent progress for each approach, both experimentally and theoretically. The emphasis is on those methods that lead to macromolecularly adsorbed layers. Practical aspects apart, we also discuss a number of interesting fundamental questions that each approach raises

On the structural polydispersity of random copolymers adsorbed at interfaces : comparison of surface and bulk distributions

Synthesis of random copolymers leads to a structurally polydispersed distribution of polymer chains, where one of the constituent monomers prefer residing on the interface, while the others have a tendency for remaining in the bulk. Previous studies have demonstrated the very strong dependence of the level of adsorption with the degree of blockiness and number of adsorbing residues of the chains. Using self-consistent field (SCF) calculations, we obtain the distribution of the adsorbed copolymers and compare this with the bulk distribution of such chains. In our study, the whole range of structurally polydisperse chains in the distribution derived for a given random copolymer, are simultaneously present and can compete with each other for adsorption. We show that the distribution of chains on the surface is grossly different to that in the bulk and is largely dominated by those rare chains at the tail end of the latter distribution

Local membrane length conservation in two-dimensional vesicle simulation using multi-component lattice Boltzmann Equation Method.

We present a method for applying a class of velocity-dependant forces within a multi-component lattice Boltzmann equation simulation which is designed to recover continuum regime incompressible hydrodynamics. This method is applied to the problem, in two dimensions, of constraining to uniformity the tangential velocity of a vesicle membrane implemented within a recent multi-component lattice Boltzmann simulation method, which avoids the use of Lagrangian boundary tracers. The constraint of uniform tangential velocity is carried by an additional contribution to an immersed boundary force, which we derive here from physical arguments. The result of this enhanced immersed boundary force is to apply a physically appropriate boundary condition at the interface between separated lattice fluids, defined as that region over which the phase-field varies most rapidly. Data from this enhanced vesicle boundary method are in agreement with other data obtained using related methods (e.g. T. Krüger, S, Frijters, F. Günther, B. Kaoui and J. Harting, Eur. Phys. J. 222, 177 (2013)) ) and underscore the importance of a correct vesicle membrane condition

Simulation of stress-assisted localised corrosion using a Cellular Automaton Finite Element approach

In this paper, the overall corrosion damage process is modelled sequentially using cellular automata (CA) to describe the localised corrosion component, and finite element analysis (FEA) to account for the mechanical component resulting from the stress concentration effect of the corrosion defect (pit). Synchronous execution of the CA and FEA, and provision of feedback between both provides a good approximation of stress-assisted pit development. Qualitative and quantitative comparison of simulation results with experimental measurements show good agreement. In particular, the model shows that mechanical effects, notably plastic strain, accelerates the rate of development of localised corrosion

Detachment force of particles with pinning of contact line from fluid bubbles/droplets

Deformation of a spherical droplet or bubble, containing a pair of particles on its surface is considered when equal but opposite forces are applied to the particles. The particles are placed opposite each other thus providing a symmetrical problem which is more amenable to analytical treatment. We extend our previous calculations, concerning such arrangements with constant contact angles, to situations where now it is the contact line that is pinned on the surface of the particles. The force-displacement curves are calculated as the particles are pulled apart and was found to be linear for small displacements. However, it is also found that the "Hookean constant" for the pinned contact line problem is different to one derived for systems with a constant contact angle, being larger if the pinned line is at the equator of the particles

Detachment force of particles from fluid droplets

We calculate the deformation of a spherical droplet, resulting from the application of a pair of opposite forces to particles located diametrically opposite at the two ends of the droplet. The free-energy analysis is used to calculate the force–distance curves for the generated restoring forces, arising from the displacement of the particles relative to each other. While the logarithmic dependence of the “de Gennes–Hooke” constant on the particle to droplet size ratio, ν, is rather well known in the limit of very small ν, we find that for more realistic particle to droplet size ratios, i.e. ν = 0.001 to 0.01, the additional constant terms of O(1) constitute a significant correction to previously reported results. We derive the restoring force constant to be 2πγ[0.5 − ln(ν/2)]−1, in perfect agreement with the exact semi-numerical analysis of the same problem. The deviation from the linear force–displacement behaviour, occurring close to the point of detachment, is also investigated. A study of the energy dissipated shows it to be an increasingly dominant component of the work done during the detachment of the particles, as ν decreases. This indicates the existence of a significantly higher energy barrier to desorption of very small particles, compared to the one suggested by their adsorption energy alone. The influence of the line tension on the detachment force is also considered. It is shown that where line tension is important, the contact angle is no longer a constant but instead alters with the displacement of the particles from their equilibrium positions

Bulk viscosity of gaseous argon from molecular dynamics simulations.

The bulk viscosity of dilute argon gas is calculated using molecular dynamics simulations in the temperature range 150-500 K and is found to be proportional to density squared in the investigated range of densities 0.001-1 kg m-3. A comparison of the results obtained using Lennard-Jones and Tang-Toennies models of pair interaction potential reveals that the value of the bulk viscosity coefficient is sensitive to the choice of the pair interaction model. The inclusion of the Axilrod-Teller-Muto three-body interaction in the model does not noticeably affect the values of the bulk viscosity in dilute states, contrary to the previously investigated case of dense fluids