Colloidal fluids

Model colloids have a number of properties that make them experimentally convenient and interesting systems to study. For instance, the timescale for stmctural relaxation of a colloidal fluid can be estimated as the time for a particle to diffuse a distance equal to its radius,... 

FIG. 8 A colloidal fluid confined within a cylindrical pore. 

Y. Sakazaki, S. Masuda, J. Onishi, Y. Chen, and H. Ohashi, The modeling of colloidal fluids by the real-coded lattice gas, Math. Comput. Simulation 72, 184 (2006). 

To fully understand the anomalous dynamics of an attractive colloidal fluid from a free-volume perspective, one must consider two effects of attractions on free volumes.75 First, attractions increase the average local space available to the particles and render the free-volume distribution more inhomogeneous than when no attractions exist. These changes act to increase the mobility of the fluid. Second, strong attractions also lead to long-lived... 

Figure 9 Properties of the attractive colloidal fluid investigated in Ref. 75 (a) self-diffusivity and (b) average free volume versus strength of the interparticle attraction (c) self-diffusivity versus average free volume for the hard-sphere fluid (open circles) and the attractive colloidal fluid (closed circles). Data compiled from Ref. 75.

Figure 10 (a) Free-volume persistence time extracted from the free-volume autocorrelation function (Eq. [9]) for an attractive colloidal fluid as a function of the strength of the interparticle attraction, (b) Comparison of colloidal self-diffusivity (closed symbols) with that estimated using the free-volume scaling relationship D — A(v )2 /tf discussed in the text (open symbols). Data taken from Ref. 75. 

An analogy may be drawn between the phase behavior of weakly attractive monodisperse dispersions and that of conventional molecular systems provided coalescence and Ostwald ripening do not occur. The similarity arises from the common form of the pair potential, whose dominant feature in both cases is the presence of a shallow minimum. The equilibrium statistical mechanics of such systems have been extensively explored. As previously explained, the primary difficulty in predicting equilibrium phase behavior lies in the many-body interactions intrinsic to any condensed phase. Fortunately, the synthesis of several methods (integral equation approaches, perturbation theories, virial expansions, and computer simulations) now provides accurate predictions of thermodynamic properties and phase behavior of dense molecular fluids or colloidal fluids [1]. 

New Paradigms for Spreading of Colloidal Fluids on Solid Surfaces... 

Chengara A (2003) Spreading of colloidal fluids on solid surfaces. PhD thesis, Illinois Institute of Technology... 

VanDamme, H., Flow and interfacial instabilities in Newtonian and colloidal fluids (or the birth, life and death of a fractal), The Fractal Approach to Heterogeneous Chemistry, edited by D. Avnir, Wiley, Chishester, 1989, pp. 199-226. 

William Russel May I follow up on that and sharpen the issue a bit In the complex fluids that we have talked about, three types of nonequilibrium phenomena are important. First, phase transitions may have dynamics on the time scale of the process, as mentioned by Matt Tirrell. Second, a fluid may be at equilibrium at rest but is displaced from equilibrium by flow, which is the origin of non-Newtonian behavior in polymeric and colloidal fluids. And third, the resting state itself may be far from equilibrium, as for a glass or a gel. At present, computer simulations can address all three, but only partially. Statistical mechanical or kinetic theories have something to say about the first two, but the dynamics and the structure and transport properties of the nonequilibrium states remain poorly understood, except for the polymeric fluids. 

Oil well drilling muds (thickener, protective colloid, fluid loss additive)... 

Thus, in the fluid state, there are two relaxation processes, the a and the with relaxation times that scale with proximity to the critical point with differing exponents, -y and — l/2fl, respectively. For spherical particles, y — 2.58 and l/2a = 1.66 thus the a process is predicted to slow more dramatically as the transition is approached than the process. Figure 4-22 shows the relaxation times t and extracted from the relaxation data of Fig. 4-20 for the colloidal fluids. The power laws given by Eqns. (4-33) and (4-34) fit these experimental concentration dependencies well, supporting the mode-coupling theory of this transition. 

Rackow E C, Weil M H, Macneil A R et al 1987 Effects of crystalloid and colloid fluids on extravascular lung water in hypoproteinemic dogs. Journal of Applied Physiology 62 2421-2425... 

Vaupshas H J, Levy M 1990 Distribution of saline following acute volume loading postural effects. Clinical and Investigative Medicine 13 165-177 Velanovich V 1989 Crystalloid versus colloid fluid resuscitation a meta-analysis of mortality. Surgery 105 65-71 Vukmir R B, Bircher N G, Radovsky A et al 1995 Sodium bicarbonate may improve outcome in dogs with brief or prolonged cardiac arrest. Critical Care Medicine 23 515-522 Walton R J 1979 Effect of intravenous sodium lactate on renal tubular reabsorption of phosphate in man. Clinical Science 57 125-127... 

Fig. 7 Reprinted with permission from [111], copyright (2004), Institute of Physics Publishing. Confocal images (yz, 75p.mx56gm, 512x512 pixels-) of a colloidal fluid at various shear conditions taken in a counter-rotating cone-plate shear cell [111] see Sect. 2.3. The applied shear rates are 1.67,3.36 and 8.39 s (fop to bottom)-, the ratios ofthe applied cone to plate rotation speeds are 84, 129 and 175 (left to right). Graphs (a) and (b) show displacement profiles, y(z). measured from these images via cross-correlation of scanned lines. The appropriate profile is overlaid on each image (white curves). The velocity profiles (dy/dz) calculated from these displacement profiles are shown in the graphs (c) and (d). The particle diameter is 1.50 pm...

We claim that evolutions of the glass temperature in vitrifying colloidal fluids and molecular liquids are analogous, even including the possibility of the reverse vitrification or devitrification on pressuring. However, for molecular liquids the negative pressures domain of isotropically stretched liquid has to be taken into account. Then, a link between molecular and colloidal glasses, often considered as separate cases so far, seems to be possible... 

Some commercial sensors meet this criterion, R,/R, > 0.99. However, they are only adequate to homogeneous or colloidal fluids, which have particles below... 

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