Liquids in Colloidal Regime

Newstein, M. C., Wang, H., Balsara, N. P. et al. 1999. Microstructural changes in a colloidal liquid in the shear thinning and shear thickening regimes. J. Chem. Phys. Ill, 4827. 

A colloidal dispersion comprises a collection of small particles, droplets, or bubbles of one phase, having at least one dimension between about 1 and 1000 nm, and dispersed in a second phase. Either or both phases may be in gas, liquid, solid, or supercritical phase states. Matter of colloidal size, just above atomic dimensions and overlapping with the emerging regime of nanotechnology, exhibits physicochemical properties that differ from those of the constituent atoms or molecules yet are also different from macroscopic material. 

In the absence of suspended solutes or colloids, the pure solvent flux through an ultrafiltration membrane is directly proportional to the applied pressure difference and inversely proportional to the viscosity of the solvent and the membrane thickness. Transport within the pores occurs in the creeping flow regime, since kinematic viscosities of liquids are sufficient to make Re < C 1 for practical pore sizes. In the simplest case, the membrane can be considered to be a packed array of straight, equal diameter nonintersecting capillary tubes. The observed volumetric flux, nAvA (cc/sec cm2), equals the product of the mass flux of solvent based on the total membrane area, nA... 

Although the true nature of the catalyst is not always clear when mononuclear complexes are used as pre-catalysts in hydrogenation reactions, with cluster compounds employed as the pre-catalyst, it is frequently found that the active species is colloidal and review articles are available on how to distinguish between homogeneous and heterogeneous regimes.[43,441 A summary of hydrogenation reactions with metal-clusters in ionic liquids is provided in Table 3.4. 

Colloid mill. This type of mill is used extensively in the food industry. A colloid mill is a conical rotator that turns in a stator of the same shape, leaving a very narrow gap between rotor and stator. The liquid is introduced from the top, and flows through the narrow gap. Due to the high rotation rate, and the small size of the gap, the shear forces are very intense, and small droplet sizes can be realized. The regime the mill operates at depends on the viscosity of the mixture. When the mixture is highly viscous, the flow will be laminar. The transition towards turbulent flow is given by the Reynolds number, which characterizes the flow ... 

Liquid-liquid emulsions and other microstructured fluids have been the subject of much academic and industrial interest, for they offer a new area for scientific research, and their behavior influences many engineering technologies indeed they represent the backbone of several emerging chemical and biochemical processes. Colloids are in a transition domain between macroscopic and microscopic regimes of matter and... 

Table 4.2 Fundamental aggregation regime for colloidal particles in a quiescent liquid (based on Femandez-Toledano et al. 2007)...

Abstract We explored the structural effects induced by the addition of salt on lipid-based liquid crystalline drops stabilized in aqueous media by charged sphere-like colloids. This allows us to distinguish two different stabilization regimes. In one case, the internal liquid crystalline phase has the ability to reorganize upon the coalescence of the drops and in the other not. This in turn depends mainly on the contact angle and the internal phase viscosity. 

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