Protective colloid effect

Colloids are either hydrophilic (water-loving) or hydrophobic (water-hating). Hydrophilic colloids (e.g., proteins, humic substances, bacteria, viruses, as well as iron and aluminum hydrated colloids) tend to hydrate and thereby swell. This increases the viscosity of the system and favors the stability of the colloid by reducing the interparticle interactions and its tendency to settle. These colloids are stabilized more by their affinity for the solvent than by the equalizing of surface charges. Hydrophilic colloids tend to surround the hydrophobic colloids in what is known as the protective-colloid effect, which makes them both more stable. 

ENZYMATIC HYDROLYSIS OF STARCH. Starch is a substance used for storing energy reserve in plants, where it is deposited in the form of starch granules. Starch may be noticed in fruit juice as a milky haze. This haze disappears when the juice is heated, but re-appears after it is cooled to less than 10°C. Like pectin, starch has a protective colloid effect on suspended particles and thus makes juice clarification more difficult. 

The impact of the protective colloid effect on the bitartrate stabilization of a wine varies according to the winemaking methods used. Red wines have a higher phenol content than white wines, and then-condensed tannins have a strong inhibiting effect. 

It is normal to find potassium bitartrate crystals, associated with precipitated condensed coloring matter, in wine with several years aging potential. When phenols condense, they become bulky, precipitate and are no longer able to express their protective colloid effect. 

Hayakawa K, Kawaguchi M, Kato T. Protective colloidal effects of hydroxypropyl methyl cellulose on the stabUity of sUicone oil emulsions. Langmuir 1997 13 6069-6073. 

Mutual adsorption of ultramicrons. For instance, protective colloidal effects. 

High levels of rot in the harvest increase juice turbidity and make clarification difficult, due to the protective colloidal effect of glucan produced by Botrytis. A low concentration of rot (less than 5%) tends to facilitate juice clarification, due to a pectinase activity in contaminated grapes that is nearly 100 times higher than in healthy grapes. 

There are three important processes for preparing PVAc latexes in the presence of PVA as a protective colloid batch, semi-continuous, and delayed addition of monomer [10]. In this Chapter, the effects of the addition of VAc and initiators on the properties of PVAc latexes are discussed using the three methods under the same charge of ingredients for polymerization as shown in Fig. 1 [1,11]. 

A separate class of materials, known as protective colloids, exerts a stabilizing influence by acting as a bridge between the continuous phase and the particles which they envelop. In many instances the optimum stabilizing effect is achieved when the protective colloids are used in conjunction with a compatible interfacial tension depressant. The protective colloid must have an affinity for the continuous phase. When stabilization occurs through protective colloidal action, the particles lose their surface property identities in respect to charge, agglomeration, etc., and assume the properties of the protective colloid. 

A study was made of the comparative stabilities at various exposures of an upset stomach remedy suspension. This product consisted of a dispersion of bismuth subsalicylate and phenylsalicylate in an aqueous system. Methyl-cellulose and magnesium aluminum silicate were selected as the suspending agents, because the presence of polyvalent metallic ions precluded the use of hydrocolloids affected by these ions. In addition, it was found that methyl-cellulose contributed a demulcent effect. The viscosity, as well as the suspension characteristics of the combination of protective colloids used, was of a synergistic nature. These colloids formed a thixotropic system. The thixotropy undoubtedly aids in stabilizing this system. In order to make this product palatable and impart elegance, color and flavor were added. Sample 1 (with protective colloids) showed no separation, while sample 2 (without... 

Kreuter and Speiser [77] developed a dispersion polymerization producing adjuvant nanospheres of polymethylmethacrylate) (PMMA). The monomer is dissolved in phosphate buffered saline and initiated by gamma radiation in the presence and absence of influenza virions. These systems showed enhanced adjuvant effect over aluminum hydroxide and prolonged antibody response. PMMA particles could be distinguished by TEM studies and the particle size was reported elsewhere to be 130 nm by photon correlation spectroscopy [75], The particle size could be reduced, producing monodisperse particles by inclusion of protective colloids, such as proteins or casein [40], Poly(methylmethacrylate) nanoparticles are also prepared... 

Methods of condensation in which protective colloids are employed, thus effecting condensation in the presence of a disintegrating agent, are largely employed for the preparation of stable suspensions, thus the precipitation of gold, platinum and palladium in thepresence of gum arabic or the protalbic and lysalbic acids of Paal by means of reducing agents such as hydroxylamine, hydrazine, or formaldehyde readily results in the formation of remarkably stable suspensions. 

In the presence of alcohols, photoreduction occurs more easily. Ketones like acetone can act as a sensitizer in this case (9). Surfactants can be used as protective colloids instead of polymers (10). Irradiation with 60Co y-rays is more effective for the reduction of metal ions (11). 

Thus, starch has a high gold number, which shows that it is an ineffective protective colloid, while gelatin has a small gold number and is thus an effective protective colloid. 

The stabilizing function of macromolecular surfactants in solid-liquid systems is exercised through protective colloid action. To be effective, they must have a strong solution affinity for hydrophobic and hydrophilic entities. In liquid-liquid systems, surfactants are more accurately called emulsifiers. The same stabilizing function is exercised in gas-liquid disperse systems where the surfactants are called foam stabilizers. 

Poly(vinyl acetate) emulsions are excellent bases for water-resistant paper adhesives destined for use in manufacturing bags, tubes, and cartons. Glue-lap adhesives, which require moderate-to-high resistance to water, exemplify this type. When routine water resistance is required, a homopolymer vinyl acetate emulsion containing a cellulosic protective colloid is effective for most purposes. Next effective are emulsions containing fully hydrolyzed poly(vinyl alcohol) as a protective colloid, followed by those containing partially hydrolyzed poly(vinyl acetate). 

Adhesives. Poly(vinyl alcohol) is used as a component in a wide variety of general-purpose adhesives to bond cellulosic materials, such as paper and paperboard, wood textiles, some metal foils, and porous ceramic surfaces, to each other. It is also an effective binder for pigments and other finely divided powders. Both fully and partially hydrolyzed grades are used. Sensitivity to water increases with decreasing degree of hydrolysis and the addition of plasticizer. Poly(vinyl alcohol) in many applications is employed as an additive to other polymer systems to improve the cohesive strength, film flexibility, moisture resistance, and other properties. It is incorporated into a wide variety of adhesives through its use as a protective colloid in emulsion p olymerization. 

Osmium Hydrosol or Colloidal Osmium is readily prepared by reducing potassium osmate, K20s04, with hydrazine hydrate in the presence of some protective colloid such as gum acacia 2 or lysalbate (or protalbate) of sodium.3 The reduction may be effected with acrolein 4 if desired. 

As mentioned above, the stability of colloidal metal solutions is considerably enhanced by the addition of certain organic substances or protective colloids. For example, gelatin has been frequently employed, 0-5 gram per litre of colloidal solution proving very effective in preventing the coagulation or precipitation of the metal.2 Extracts of Iceland moss3 and of quince seed 4 have also been recommended. 

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