Hydrodynamic interactions, role

Groot R D, T J Madden and D J Tildesley 1999. On the Role of Hydrodynamic Interactions in Bloc Copolymer Microphase Separation. Journal of Chemical Physics 110 9739-9749. 

There are several attractive features of such a mesoscopic description. Because the dynamics is simple, it is both easy and efficient to simulate. The equations of motion are easily written and the techniques of nonequilibriun statistical mechanics can be used to derive macroscopic laws and correlation function expressions for the transport properties. Accurate analytical expressions for the transport coefficient can be derived. The mesoscopic description can be combined with full molecular dynamics in order to describe the properties of solute species, such as polymers or colloids, in solution. Because all of the conservation laws are satisfied, hydrodynamic interactions, which play an important role in the dynamical properties of such systems, are automatically taken into account. 

Most descriptions of the dynamics of molecular or particle motion in solution require a knowledge of the frictional properties of the system. This is especially true for polymer solutions, colloidal suspensions, molecular transport processes, and biomolecular conformational changes. Particle friction also plays an important role in the calculation of diffusion-influenced reaction rates, which will be discussed later. Solvent multiparticle collision dynamics, in conjunction with molecular dynamics of solute particles, provides a means to study such systems. In this section we show how the frictional properties and hydrodynamic interactions among solute or colloidal particles can be studied using hybrid MPC-MD schemes. 

Hydrodynamic interactions with particles may certainly play a role in clustering. Horio and Clift [30] noted that particle clusters, a group of loosely held together particles, are the result of hydrodynamic effects. Squires and Eaton [31] proposed that clustering resulted from turbulence modification from an isotropic turbulent... 

In general, the motion of a polymer chain in solution is governed by intermolecular interaction, hydrodynamic interaction, Brownian random force, and external field. The hydrodynamic interaction consists of the intra- and intermolecular ones. The intramolecular hydrodynamic interaction and Brownian force play dominant roles in dilute solution, while the intermolecular interaction and the intermolecular hydrodynamic interaction become important as the concentration increases. 

The physical nature of this phenomenon is related to the presence of hydrodynamic interactions described by the Oseen tensor [22, 25]. The role of the finely porous medium in classical electroosmosis is played in this case by the gel which can be roughly considered as a collection of pores of size where is the mesh size of the gel [22]. 

This result was interpreted by the manifestation of short range hydrodynamic interactions. The role of electrostatic interaction in flotation is confirmed by investigations of the influence of added sodium dodecylsulfate (SDS). Due to SDS adsorption the charge of bubbles increases und the collision efficiency decreases. When following the capture rate it is observed, that at SDS concentrations above 10 M particle deposition completely stops while the contact angle continues to be large. Thus, electrostatic repulsion prevents the contact between particles and bubbles. 

Dynamic adsorption layers (DAL) influence practically all sub-processes which manifest themselves in particle attachment to bubble surfaces by collision or sliding. Surface retardation by DAL affects the bubble velocity and the hydrodynamic field and consequently the bubble-particle inertial hydrodynamic interaction. It also affects the drainage and thereby the minimum thickness of the liquid interlayer achieved during a first or second collision or sliding. Thus elementary acts of microflotation and flotation is systematically considered in this book for the first time with accoimt of the role of DAL. Extreme cases of weakly and strongly retarded bubble surfaces are discussed which assists to clarify the influence of bubble and particles sizes on flotation processes. 

The role of hydrodynamic interaction in Brownian diffusion was discussed in Section 8.2. Consider now its effect on turbulent coagulation. Formally, it can be taken into account in the same manner as in Brownian motion, by introducing a correction multiplier into the factor of turbulent diffusion (10.57). Another, more correct way (see Section 11.3) is to use the Langevin equation that helped us determine the factor of Brownian diffusion in Section 8.2. As was demonstrated in [60], the factor of turbulent diffusion is inversely proportional to the second power of the hydrodynamic resistance factor ... 

We have introduced three characteristic lengths 1, i e> and to describe the effects of chain overlap on the density fluctuation correlation, the intrachain excluded-volume interaction, and the intrachain hydrodynamic interaction, respectively. In the following chapters, we will illustrate the important roles played by them in understanding the static and dynamic behavior of polymer solutions. 

The comparatively lowest importance have the hydrodynamic interactions, their role is important at low concentration of the solid phase in the suspension. In the pastes, in which the share of solid phase is substantial, the electrostatic and van der Waals forces are dominating. Moreover, because of the high surface tension of water and the presence of air in the paste, between cement grains the attractive capillary forces appear. They prevail at the grain size from 1 to 0.1 mm. The maximum capillary stress is given by the following Carman formula ... 

Abstract. The stability of suspensions/emulsions is under consideration. Traditionally consideration of colloidal systems is based on inclusion only Van-der-Waals (or dispersion) and electrostatic components, which is refereed to as DLVO (Derjaguin-Landau-Verwey-Overbeek) theory. It is shown that not only DLVO components but also other types of the inter-particle forces may play an important role in the stability and colloidal systems. Those contributions are due to hydrodynamic interactions, hydration and hydrophobic forces, steric and depletion forced, oscillatory structural forces. The hydrodynamic and colloidal interactions between drops and bubbles emulsions and foams are even more complex (as compared to that of suspensions of solid particles) due to the fluidity and deformability of those colloidal objects. The latter two features and thin film formation between the colliding particles have a great impact on the hydrodynamic interactions, the magnitude of the disjoining pressure and on the dynamic and thermodynamic stability of such colloidal systems. 

Adopting a different point of view, we tried to fit the variation of D versus (p at low (j) with existing theories taking into account the role of hydrodynamic interactions and interparticle forces. This has been done for microemulsions A and B, using Felderhof theory (11) with an interaction potential sum of hard sphere repulsion and W = A(2R/r), A = B. The agreement with experimental a values is quite satisfactory. 

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