Phase separation in colloids

Stability in mixtures of colloidal particles and polymer molecules, dispersed in a solvent, has been the subject of experimental and theoretical investigations for a long time and it has applications in diverse fields such as paint technology, wastewater treatment, emulsion polymerization, biology etc. It has now been well recognized that polymer molecules can be used to induce either stabilization or flocculation (phase separation) in colloidal dispersions. It is important to distinguish between polymers which are adsorbed on the particle surface and those that are free in solution because the two situations usually lead to qualitatively different effects. Stability imparted by adsorbed polymers is known as steric stabilization and the flocculation or phase separation caused by the free polymer is due... 

These results demonstrate that nonadsorbing polymer can induce phase separations in colloidal systems with the nature of the phases depending primarily on the ratio of the particle and polymer sizes. Since the strength of the attraction is not necessarily a monotonic function of the polymer concentration, e.g., because of penetration of the free polymer into a grafted layer, both destabilization and restabilization are possible. 

Tuinier, R., Rieger, J., and de Kmif, C.G. (2003). Depletion-induced phase separation in colloid-polymer mixtures. <7v. ColloidInterf. Sci. 103, 1-31. 

Verhaegh, N.A.M., van Duijneveldt, J.S., Dhont, J.K.G., and Lekkerkerker H.N.W. 1996. Fluid-fluid phase separation in colloid-polymer mixtures studied with small angle light scattering and light microscopy. PhysicaA 230 409-436. 

Jansen J W, de Kruif C G and Vrij A 1986 Attractions in sterically stabilised silica dispersions. I. Theory of phase separation J. Colloid Interface Sc/. 114 471-80... 

Vincent B, Edwards J, Emmett S and Greet R 1988 Phase separation in dispersions of weakly-interacting particles in solutions of non-adsorbing polymers Colloid Surf. 31 267-98... 

Gast A P, Flail C K and Russel W B 1983 Polymer-induced phase separations in nonaqueous colloidal suspensions J. Colloid Interface Sol. 96 251 -67... 

The above model assumes that both components are dynamically symmetric, that they have same viscosities and densities, and that the deformations of the phase matrix is much slower than the internal rheological time [164], However, for a large class of systems, such as polymer solutions, colloidal suspension, and so on, these assumptions are not valid. To describe the phase separation in dynamically asymmetric mixtures, the model should treat the motion of each component separately ( two-fluid models [98]). Let Vi (r, t) and v2(r, t) be the velocities of components 1 and 2, respectively. Then, the basic equations for a viscoelastic model are [164—166]... 

C. A. Miller, R.-N. Hwan, W.J. Benton, and T.J. Fort Ultralow Interfacial Tensions and Their Relation to Phase Separation in Micellar Solutions. J. Colloid Interface Sci. 61,554(1977). 

A.P. Gast, C.K. Hall, and W.B. Russel Polymer-Induced Phase Separations in Nonaqueous Colloidal Suspensions. J. Colloid Interface Sci. 96, 251 (1983). 

B. Vincent, J. Edwards, S. Emmett, and R. Croot Phase Separation in Dispersions of Weakly Interacting Particles in Solutions of Non Adsorbing Polymer. Colloids Surfaces 31, 267 (1988). 

S. Sanyal, N. Easwear, S. Ramaswamy, and A.K. Sood Phase Separation in Binary Nearly-Hard-Sphere Colloids Evidence for the Depletion Force. Europhys. Lett. 18, 107 (1993). 

Maeda, Y. Hachisu, S. (1983) Schiller layers in y-ferric oxyhydroxide sol as an order-disorder phase separating system. Colloids Surfaces 6 1-6... 

Kaplan PD, Rouke JL, Yodh AG, Pine DJ (1994) Entropically driven surface phase separation in binary colloidal mixture. Phys Rev Lett 72 582-585... 

Norton I.T., Frith W.J. (2003). Phase separation in mixed biopolymer systems. In Dickinson, E., van Vliet, T. (Eds). Food Colloids, Biopolymers and Materials, Cambridge, UK Royal Society of Chemistry, pp. 282-297. 

Sengupta, T., Damodaran, S. (2000). Incompatibility and phase separation in a bovine serum albumin/p-casein/water ternary film at the air-water interface. Journal of Colloid and Interface Science, 229, 21-28. 

Experimentally the increase in activation energy is quite evident, but the cause of this increase is not clear. It can be argued that the increase in activation energy is related to a strong increase in viscosity of the reactive medium or to phase separation in the reactive mass when a newly formed polymer precipitates from a solution and forms colloid particles. The experimental data described by Eqs. (2.23) - (2.25) can also be treated in ways other than those used in the original publication. For example, it is possible to linearize the exponential factor in Eq. (2.23), as was done above for other purposes. Then for the range of P from 0.35 to 0.8 we can write ... 

One interesting feature of the HC formulae is that phase separation is predicted when there is a small concentration of large spheres [21]. There is some earlier numerical data from integral equations [52-54] indicating that phase separation occurs in asymmetric hard sphere mixtures. This may shed light on recent experimental results [55-65] who have observed evidence of phase instability in colloidal suspensions. 

From the above summary of experimental investigations into Uving miniemulsion polymerization, we can see that controlled mini emulsion polymerization (SFRP, ATRP, and RAFT) is less colloidal-stable during polymerization than its non-living counterpart. Colloidal instability leads to phase separation in the worst cases. In improved cases, the latex that results from the controlled mini-... 

Rescic, J., and Linse, P. Gas-liquid phase separation in charged colloidal systems. Journal of Chemical Physics, 2001, 114, No. 22, p. 10131-10136. 

The volume restriction effect as discussed in this paper was proposed several years ago by Asakura and Oosawa (12,13). Their theory accounted for the instability observed in mixtures of colloidal particles and free polymer molecules. Such mixed systems have been investigated experimentally for decades (14-16). However, the work of Asakura and Oosawa did not receive much attention until recently (17,18). A few years ago, Vrij (19) treated the volume restriction effect independently, and also observed phase separation in a microemulsion with added polymer. Recently, DeHek and Vrij (20) have reported phase separation in non-aqueous systems containing hydrophilic silica particles and polymer molecules. The results have been treated quite well in terms of a "hard-sphere-cavity" model. Sperry (21) has also used a hard-sphere approximation in a quantitative model for the volume restriction flocculation of latex by water-soluble polymers. 

Miller, C.A. et ah, Ultralow interfacial tensions and their relation to phase separation in micellar solutions, J. Colloid Interface Sci., 68, 221, 1977. 

Kaplan, P.D. et al., EntropicaUy driven surface phase separation in binary colloidal mixtures, Phys. Rev. Lett, 72, 582, 1994. 

Broad screening of the possible donor solvents proved that only a few solvents are suitable for use in phase separation and colloid stabilization. By far the best results are obtained with propene carbonate (Table 1), which is favored by the high selectivity to C18 1 and the short reaction time. 

In the forementioned laboratories, we started with a new strategy based on phase separation in order to prepare natural particles. Simple or complex coacervation methods involving proteins or protein and polysaccharide mixtures3 were used to create new matrices dedicated to controlled release applications. The colloidal carriers produced were in the micrometre or nanometre size range depending on the substrates or the methods used. Wheat proteins, gliadins, were implicated in simple coacervation to produce nanospheres. Controlled release experiments with model compounds were conducted in order to evaluate... 

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