Colloids, freezing stability

Latexes constitute a subgroup of colloid systems known as lyophobic sol. Sometimes they are called polymer colloids. The stability of these colloids is determined by the balance between attractive and repulsive forces affecting two particles as they approach one another. Stability is conferred on these latexes by electrostatic forces, which arise because of the counterion clouds surrounding the particles. Other forces of an enthalpic or entropic nature arise when the lyophilic molecules on the surfaces of the latexes interact on close approach. These can be overcome by evaporation of the water, heating, freezing, or by chemically modifying the surfactant, such as by acidification. 

K Heinzelmann, K Franke. Using freezing and drying techniques of emulsions for the microencapsulation of fish oil to improve oxidation stability. Colloids Surfaces B Biointerfaces 12(3—6) 223—229, 1999. 

Temperature Sensitivity. Samples of Au-acetone colloid were subjected to boiling and freezing. Upon returning to room temperature the colloids remained stable and no flocculation had occurred. These results indicate that steric stabilization33,43) (solvation) is a very important mechanism. Charge-stabilized colloids generally flocculate when subjected to such extremes of temperature.(56)... 

With selenium sols prepared by means of hydrazine hydrate at the ordinary temperature, by pouring into a large volume of water it has been shown that the stability of the colloid depends mainly on the degree of dispersion. An optimum concentration of electrolyte is necessary for the stability of the hydrosols. In the absence of electrolytes the system is quite unstable towards freezing. 

Mixtures of anionic and nonionic surfactants are usually employed. The anionic emulsifiers are the less water soluble and control the number and size of the particles. The nonionic surfactants are often ethylene oxide condensates of alkyl phenols their water solubility is proportional to ihedcgree of polymerization of the poly(ethylene oxide) component. Their function is primarily to provide colloidal stability against electrolytes, mechanical shearing, and freezing. 

After fermentation, wine becomes supersaturated with potassium bitartrate. The removal of this excess is necessary to avoid sedimentation after the wine is bottled. A cold stabilization technique where the wine is chilled just above its freezing point is generally used. Protective colloids, which prevent the crystaH ization of the excess potassium bitartrate make a wine resistant to cold stabilization even during prolonged refrigeration. In those... 

This work will describe a series of magnetic colloidal systems that were specifically developed for an application in ink jet printing technology. This application imposes a certain set of requirements such as particle size 100 + 50A, magnetic moment of 25 emu/g or 35%w Fe O in colloidal dispersion, viscosity of 8-10 cps, non-toxic aqueous system, shelf life of a few years, freeze-thaw stability, fast drying (2 msec) and high optical density of magnetic ink on various papers. 

The use of Cremophore EL in the microemulsions is avoided nowadays due to several adverse effects such as anaphylactic shocks and histamine release [20 ]. The other important consideration is the concentration of surfactants and co-surfactants which should be minimal and preferably not exceed 20%. Furthermore, it is necessary to ensure that the microemulsion structure is preserved in the presence of the tonicity adjusting solutions such as 0.9% saline solution and preservatives. The parenteral microemulsions should also be able to withstand tests such as freeze-thaw cycling which ensure their physical stability. It has been shown that the colloidal carriers based on Solutol HS 15 can withstand freeze-thaw cycling very efficiently whereas lecithins can offer stability to autoclaving [ 112 ]. Cosurfactants such as benzyl alcohol cannot be used for intravenous applications but can be used for the small volume parenteral products up to the concentration of 1% w/v. Ethanol at concentrations above 10% usually results in the pain on injection. Co-surfactants such as glycofurol are reported to acceptable for parenteral products but there are no products based on glycofurol available for the human use. The pyrrolidone derivatives are reported to be acceptable for veterinary applications. 

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