Colloidal silica physicochemical properties

In addition, when the degree of division is increased, the proportion of atoms on the interfaces also grows. To take the example of the silica, whereas the proportion of Si02 constituents in the material at the surface of the particles is infinitesimal for the 1 mm beads, it reaches 20% for the 10 nm beads. The importance of interfaces for the physicochemical properties of colloidal systems is clear. 

Charged colloids in solution are ubiquitous in a wide variety of biological and technical systems. Some examples are proteins made by amino acids, micelles formed by charged surfactants or charged block copolymers, microemulsions formed by water, oil, and charged surfactants, silica particles made by silica oxide, and polystyrene based latex particles. In these systems, the physicochemical properties are to a large degree determined by electrostatic forces. Despite extensive studies of these forces for the last 50 years, the electrostatic interactions in such systems remain a central problem in colloidal science [1,2]. 

AFM force measurements can be done with a range of surfaces. Conventional AFM tips, however, should not be used for quantitative interfacial force measurements because quantitative comparison with theoretical predictions requires that the radius of the approaching probe be much greater than the separation distance. The latter point has often been overlooked in surface force measurements with standard AFM tips. The coUoid-probe AFM method > > is appropriate for quantitative surface force measurements. A colloidal (usually silica) microsphere attached to the end of the AFM cantilever provides a well-defined, mathematically tractable sphere-vs-flat geometry for the scaling of forces, and allows the use of different colloid materials, or the surface modification of colloid spheres, for investigating interactions between surfaces with various physicochemical properties. 

A further advantage of PMMA relies on its availability. Uniformly sized PMMA spheres are prepared by polymerization of methyl methacrylate (MMA) in water. The product of the polymerization then takes the form of a colloidal suspension of solid particles that are so small that they tend not to settle. By centrifugation, the PMMA particles are forced to settle and pack into a solid, often called a colloidal crystal. In such colloidal crystals, the PMMA spheres are arranged in a close-packed fashion in the same manner as the silica spheres that make up natural opal [178]. Therefore, these materials can be referred to as synthetic opals. Several textbooks cover selective aspects of the physicochemical properties of PMMA [181,182]. 

Already reported CAV/0 microemulsion technique was used to prepare the MLPs [12-15]. Briefly, this technique consists of an oil phase, a colloidal water phase, and surfactants and possesses specific physicochemical properties such as transparency, isotropy, and thermodynamic stability, n-Heptane was used as the oil phase, BrijSO as surfactant and tetraethoxysilane (TEOS) as silica precursor. This method is based on the hydrolysis and the condensation of TEOS. There is a major importance to the concentration and the order of addition of the different species. To the mixture of heptane/BrijSO we add slowly a colloidal suspension of y-Fe203 MPS in water (13 mg in 750 pL of water). After 15 min of stirring we added the cluster units in a mixture of Et0H H20 (1 1). Afterward we introduce an aqueous ammonia solution (28%). Finally the TEOS was added and the microemulsion was stirred during 3 days before several precipitation/resuspension to transfer our MLPs in water. 

FIGURE 1.186 Specific surface area 5, as a function of the heating time at different temperatures for fresh nanosilica A-300 samples (a, b) No 1 and (c, d) No 2 calculated using the argon adsorption data. (Adapted from Colloids Surf. A Physicochem. Eng. Aspects, 218, Gun ko, V.M., Voronin, E.F., Mironyuk, I.F. et al.. The effect of heat, adsorption and mechanochemical treatments on stuck structure and adsorption properties of fumed silicas, 125-135, 2003g. Copyright 2003, with permission from Elsevier.)... 

Gun ko, V.M., Voronin, E.F., Mironyuk, I.F. et al. 2003g. The effect of heat, adsorption and mechanochemical treatments on stuck structure and adsorption properties of fumed silicas. Colloids Surf. A Physicochem. 

Zarko, V.I., Gun ko, V.M., Chibowski, E., Dudiuk, V.V., and Leboda, R. 1997. Study of some surface properties of pyrogenic alumina/silica materials. Colloids Surf. A Physicochem. Eng. Aspects 127 11—18. 

A. van Blaaderen and A. Vrij Synthesis and characterization of colloid dispersions of fluorescent, monodispersed silica spheres, Langmuir, 8 (1992) 2921-2931 J.D. Wells, L.K. Koopal, and A. de Keizer Monodisperse, nonporous, spherical silica particles, Colloids Surf. A Physicochem. Eng. Asp., 166 (2000) 171-176 Howard A. Ketelson, Robert Pelton, and Michael A. Brook Surface and colloidal properties of hydrosilane-modifledStOber silica. Colloids Surf. A Physicochem. Eng. Asp., 132 (1998) 229-239... 

---