Colloid stabihty

Water. The character of the water has a great influence on the character of the beer and the hardness of water (alkalinity) manifests itself by the extent of its reaction with the weak acids of the mash. Certain ions are harm fill to brewing nitrates slow down fermentation, iron destroys the colloidal stabihty of beer, and calcium ions give beer a purer flavor than magnesium or sodium ions (Table 7). 

Two kinds of barriers are important for two-phase emulsions the electric double layer and steric repulsion from adsorbed polymers. An ionic surfactant adsorbed at the interface of an oil droplet in water orients the polar group toward the water. The counterions of the surfactant form a diffuse cloud reaching out into the continuous phase, the electric double layer. When the counterions start overlapping at the approach of two droplets, a repulsion force is experienced. The repulsion from the electric double layer is famous because it played a decisive role in the theory for colloidal stabiUty that is called DLVO, after its originators Derjaguin, Landau, Vervey, and Overbeek (14,15). The theory provided substantial progress in the understanding of colloidal stabihty, and its treatment dominated the colloid science Hterature for several decades. 

Adsorption phenomena from solutions onto sohd surfaces have been one of the important subjects in colloid and surface chemistry. Sophisticated application of adsorption has been demonstrated recently in the formation of self-assembhng monolayers and multilayers on various substrates [4,7], However, only a limited number of researchers have been devoted to the study of adsorption in binary hquid systems. The adsorption isotherm and colloidal stabihty measmement have been the main tools for these studies. The molecular level of characterization is needed to elucidate the phenomenon. We have employed the combination of smface forces measmement and Fomier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR) to study the preferential (selective) adsorption of alcohol (methanol, ethanol, and propanol) onto glass surfaces from their binary mixtures with cyclohexane. Om studies have demonstrated the cluster formation of alcohol adsorbed on the surfaces and the long-range attraction associated with such adsorption. We may call these clusters macroclusters, because the thickness of the adsorbed alcohol layer is about 15 mn, which is quite large compared to the size of the alcohol. The following describes the results for the ethanol-cycohexane mixtures [10],... 

Among the many interesting current developments in this field, the properties of supramolecular polymers at interfaces have been relatively httle explored so far, but seem especially promising. This includes the preparation of supramolecular polymer brushes [167-171], of monolayers for surface nanopatterning [41] or the study of the influence of supramolecular polymers on colloidal stabihty [163]. 

Application of DLVO Theory. Some of the concepts and expressions of Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory of colloid stabihty have been described in Chapter 1, or can be found in many different textbooks 4, 5). The application of DLVO theory to oil-in-water colloids with special reference to the stability of bitumen-in-water emulsions will be discussed here. 

Ishikawa, Y, Aoki, N., and Ohshima, H., Colloidal stabihty of aqueous polymeric dispersions Effect of water insoluble excipients. Colloids Sutf. B, 45, 25, 2005. 

The condensation method begins with molecular units, and the particles are built-up by a process of nucleation typical example is the preparation of polymer lattices, in which case the monomer (e.g., styrene or methylmethacrylate) is emulsified in water using an anionic or nonionic surfactant (e.g., sodium dodecyl sulphate or alcohol ethoxylate). A polymeric surfactant is also added to ensure the long-term colloid stabiHty of the resulting latex. An initiator such as potassium persulphate is then added and, when the temperature of the system has increased, initiation occurs that results in formation of the latex [polystyrene or poly(methylmethacrylate)]. 

Descriptions of both emulsion and dispersion polymerisation are given below, with particular reference to the control of their particle size and colloid stabiHty, which is greatly influenced by the emulsifier or dispersant used. Particular emphasis will be placed on the effects of polymeric surfactants that have been recently appHed to the preparation of emulsion polymers. 

Non-grafted boehmite rods experience a much more complicated interaction potential as positive surface electrical charges now play an important role. In this case, the phase diagram has to be discussed in the frame of both the Onsager model of nematic ordering and the DLVO (named after B.V. Deryagin, L. Landau, E.J.W. Verwey, and J.T.G. Overbeek) theory of colloidal stability, which describes colloidal stabihty as a balance between repulsive electrostatic and attractive van der Waals interactions [67,68]. At low ionic strength, electrostatic repulsion dominates so that the phase stability is essentially described by the... 

The problems related to the colloidal stabihty of amphiphihc polymers in water are reviewed by Aseyev, Tenhu, and Winnik in the first chapter of volume 196. The focus is on the derivatives of thermally responsive smart macromolecules - both on copolymers and homopolymers - which are present in a solution as stable micelles potentially having various apphcations. 

Prog. Org. Coat. 1972, 1,23-43 (c) R. Lai-hle, K. Hamann, Formation of chemically hound polymer layers on oxide surfaces and their role in colloidal stabihty,... 

Stable suspensions of AI2O3 particles and Si02 particles are prepared separately at a pH = 6. If the two suspensions are mixed, discuss the colloidal stabihty of the resulting suspension. 

The Theoretical Basis of Latex Stabiiization. The colloidal stabihty of each class of latex is primarily dependent on the effectiveness of the sindactant. In the high permittivity of water, most polymer colloid particles carry an electric... 

Problems can consist in the chemical and colloidal stabihty, eg upon oral administration, and in the low permeation through cellular membranes. For this reason vesicles are mostly administered parenterally, ie intravenously, subcutaneously, or intramuscularly. Their tissue specificity is first confined to the cells of the reticuloendothelial system which recognizes them as foreign microparticles and transports them to liver and spleen. Their biodistribution can be regulated by surface modification, eg by placing PEO stealth systems) or monoclonal antibodies site-specific targeting) to the vesicle smface. By this means their residence time and bioavailablity can be increased (211). 

Fazio S, Colomer M T, Salomoni A, Moreno R et al. (2008) Colloidal stabihty of nanosized titania aqueous suspensions. Journal of the European Ceramic Society 28 2171-2176. 

Surfactant-free emulsion polymerization is an important industrial process for the manufacture of water-based polymeric materials with excellent water resistance and adhesion properties. In the absence of surfactant, the colloidal stability of the polymerization system can be achieved by using a persulfate initiator such as potassium persulfate. In addition to initiating free radical polymerization, the negatively charged sulfate end-groups (-SO4) of oligomeric radicals origmating from the persulfate initiator molecules, which are anchored on the surfaces of particle nuclei, act as an electrostatic stabilizer that impart colloidal stabihty to the latex particles. Due to the relatively low particle... 

Chapters 10 and 11 are devoted entirely to aspects of colloid stabihty. First, the essential concepts of the electrical and van der Waals forces between colloid particles are presented with special emphasis on the concepts of the zeta potential, double-layer thickness and Hamaker constants. Then, the DLVO theory for colloidal stability is presented. This is a major tool in colloid chemistry and we discuss how stability is affected by manipulating the parameters of by the classical DLVO theory. Chapter 11 closes with a presentation of kinetics of colloid aggregation and structure of aggregates. Chapters 12 and 13 are about emulsions and foams, respectively - two important categories of colloid systems where DLVO and other principles of colloid and surface science are apphed. In this case, DLVO is often not sufficient. Steric forces and solvation effects are not covered by the classical DLVO and their role in colloid stabihty is also discussed in Chapter 12. 

Additional surfactants are used to improve the colloidal stabihty of the adhesive formulation in construction applications or to improve the coatability of PSA. Surfactants reduce the surface tension and are used as wetting agents for the non-polar surface of a sihcon-ised release liner. They naturally increase the tendency of foaming. The sodium salt of a sulfosuccinic acid ester is a very effective surfactant, which spreads very quickly onto newly generated surfaces (during coating) to stabilise them. 

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