Colloid theory

Saunders B R and Vincent B 1999 Microgel particles as model colloids theory, properties and applications Adv. Colloid Interface Sol. 80 1 -25... 

While these are not all found for every asphalt, they constitute strong supporting evidence for the colloidal theory of asphalt structure. 

Classical theories of emulsion stability focus on the manner in which the adsorbed emulsifier film influences the processes of flocculation and coalescence by modifying the forces between dispersed emulsion droplets. They do not consider the possibility of Ostwald ripening or creaming nor the influence that the emulsifier may have on continuous phase rheology. As two droplets approach one another, they experience strong van der Waals forces of attraction, which tend to pull them even closer together. The adsorbed emulsifier stabilizes the system by the introduction of additional repulsive forces (e.g., electrostatic or steric) that counteract the attractive van der Waals forces and prevent the close approach of droplets. Electrostatic effects are particularly important with ionic emulsifiers whereas steric effects dominate with non-ionic polymers and surfactants, and in w/o emulsions. The applications of colloid theory to emulsions stabilized by ionic and non-ionic surfactants have been reviewed as have more general aspects of the polymeric stabilization of dispersions. ... 

Properties of clays and clayey rocks, and also the processes in them depend on a number of factors. Then the mathematical simulation of the properties and processes, as one of the methods of their examination, is a rather difficult problem. Physically it is clear that the speciflc properties of clay rocks (low permeability, plasticity in moist condition) are caused by the existence of clay minerals in their composition, and these properties are a manifestation of surface capacities, which exist between particles of the clay minerals, which are included in the composition of clays. The most useful conception of the activity of surface capacities is the conception of disjoining pressure between colloid particles, Mitchell (1976). In this work we provide a description of the physical and mechanical clay properties and transport processes in them. The description is based on methods of theory of filtration consolidation. Nikolaevskiy (1996), and also on the theory of stability of lyophobic colloids (theory of Deijaguin-Landau-Verwey-Overbeeck, or DLVO theory), which uses the conception of disjoining pressure. 

Puck and others used the theories of colloid stability to explain the adsorption of bacteriophage by bacteria. Their findings appeared to be compatible with those of the basic colloid theory. This work and that of Valentine and Allison " led to the novel result that initial contact between virus particles and bacterial surfaces was regulated by electrostatic repulsion and the forces that govern the double layer. While these early studies were not as successful as one might have wished, they did show a correlation between the DLVO theory and the experimental data. Though the evidence is not conclusive, the work by Curtis and Pethica also tends to show that the DLVO theory is relevant to some biological systems. Other studies done at the time tended to show little or no correlation between the DLVO theory... 

In this chapter, we have covered some of the basic elements of the Poisson-Boltzmann implicit solvent description of biomolecular electrostatics. Specifically, we have focused on the application of these methods to basic problems in computational biology. The discussion presented here is necessarily incomplete—electrostatics is a very broad field and continually changing. For additional background and more in-depth discussions of some of the principles and limitations of continuum electrostatics, interested readers should see the general continuum electrostatics texts by Jackson" and Landau et al., " the electrochemistry text of Bockris et al., the colloid theory treatise by Verwey and Overbeek, " and the fantastic collection of condensed matter electrostatics articles assembled by Holm et al. ... 

There were several scientists who had obtained results that were clearly in disagreement with colloid theory, but their contributions were ignored [1, 3, 65, 66]. A person was needed of high achievement in classical chemistiy, convinced of the macromolecular hypothesis (developed and expressed in the several decades before), of unbendable conviction that he was correct, and with the strong, even irascible character of a warrior. Herrmann Staudinger was this hero. 

Such a variation principle may be looked upon as the extension from one to three dimensions of Hamilton s Principle of Stationary Action in dynamics. We will show below that the analogous extension from one to three dimensions of Hamilton s less known Principle of Variable Action " (which regards the integral I in its dependence on both the boundary B of D and on the boundary values of ip) throws significant light on the structure of colloid theory. 

APPLICATION TO COLLOID THEORY The Lagrange function for equation (1) reads... 

The degree of stability of many dispersions cannot be explained solely on the basis of Fa and Fr. Elworthy and Florence [56] have treated the stability of emulsions of chlorobenzene and anisole stabilized with a series of synthetic polyoxyethylene ethers in the light of colloid theory and have shown that electrical stabilization alone cannot explain the stability observed. The nature of this other force which is invoked to explain discrepancies between theory and experiment is not fully worked out. Nevertheless, much interest has been shown in this alternative mechanism of stabilization, which for non-ionic emulsions appears to play the major role [64]. Results have indicated that the thickness and degree of solvation of adsorbed layers is critical [65]. Thus, the particular conformation and length of the polyoxyethylene chains of non-ionic surfactants at interfaces is likely to be an important factor in the stabilization of emulsified droplets. 

Two distinct phases of bacterial sorption on to glass have been observed [78] the first reversible phase may be interpreted in terms of DLVO theory. Reversible sorption of a non-mobile strain (Achromobacter) decreased to zero as the electrolyte concentration of the media was increased, as would be expected. The second irreversible phase is probably the result of polymeric bridging between bacterial cell and the surface in contact with it. It is obviously not easy to apply colloid theory directly but the influence of factors such as ij/o, pH and additives can be predicted and experimentally confirmed. 

Testing of Colloidal Theories or Particle Sizing with a Pinch of Salt... 

For two and a half years, Mendeleev worked actively for the Russian Navy to develop a form of smokeless gunpowder. Mendeleev did not hesitate to discuss the implications of his gunpowder for naval procedures and organization, but he did not extend the work s philosophical implications into the realm of solutions and colloid theory from which it clearly emerged. 

The publication in 1948 of a monograph by Verwey and Overbeek detailing work done by them and others during World War II on the application of the PB equation, and, in particular, the Gouy-Chapman version of it, to the study of colloids has proved to be as important as the initial publications by Gouy and Chapman and Debye and Hiickel. This study laid the foundation for the modern study of colloids and has served as the primary guidepost for most of the work described here. Today, the PB equation, and in particular the Debye-Hiickel (DH) linearized approximation, forms the foundation for modern descriptions of electrolyte and colloid theory. New theories are compared with and often derived from the nonlinear Poisson-Boltzmann equation and in the appropriate limits reduce to the DH result. As has been shown by modern statistical methods, the Debye-Hiickel theory of electrolyte solutions is analogous to the lowest-order harmonic approximation in potential theory. ... 

Saunders, B. R. and Vincent, B. 1999. Microgel particles as model colloids Theory, properties and applications. Atfv. Colloid Interface Set 80 1-25. 

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