colloids

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colloids : 

K.L.Deepthi colloids

Colloidal Dispersions : 

Colloidal Dispersions Dispersed systems consist of : a) particulate matter (dispersed phase). b) dispersion medium (continuous medium). Classification of colloids: Colloids can be classified mainly by 3 ways: Classification Based on the State of the Dispersed Phase and Dispersion Medium Classification Based on the Nature of Interaction Between Dispersed Phase and Dispersion Medium

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Table 2: Types of colloids Classification Based on the State of the Dispersed Phase and Dispersion Medium

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Classification Based on the Nature of Interaction Between Dispersed Phase and Dispersion Medium a) Multimolecular colloids  usually have lyophobic character. Ex: gold and sulphur sols b) Macromolecular colloids  resemble true solutions Ex: proteins, cellulose, starch and polymers such as polyethylene, nylon and polystyrene c) Associated colloids  type of micelle it forms depends on the nature of solvent (hydrophilic or hydrophobic) Kraft Temperature (Tk ) Critical micelle concentration (CMC) Ex: soaps and synthetic detergents Micelle

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1) Lyophilic colloids Colloidal particles interact to an appreciable extent with the molecules of the dispersion medium (solvent loving). Obtained simply by dissolving the material in the solvent (due to the high affinity) Types of lyophilic colloids;(According to type of solvent) Hydrophilic colloids: Solvent: water. Example: acacia, insulin…. in water Lipophilic colloid: Solvent: non- aqueous, organic solvent. Example: rubber &polystyrene.

2) Lyophobic colloids : 

2) Lyophobic colloids Colloidal particles have very little or no attraction for the dispersion medium (solvent hating). Colloidal particles: inorganic particles (e.g. gold, silver, sulfur….) Dispersion medium: water. Less stable as the particles surrounded only with a layer of positive or negative charge but not having solvent sheath. Once precipitated, it is not easy to reconstitute the sol by simple mixing with the dispersion medium. Hence, these sols are called irreversible sols.

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Not obtained simply i.e need special method for preparation Methods to prepare Lyophobic colloids: A) Dispersion methods: coarse particles are reduced in size by; 1) Ultrasonic generator 2) Electric arc. 3) Colloid mill. B) Condensation methods: 1)addition of non-solvent 2) Chemical reaction.

Colloidal mill : 

Colloidal mill Coarse to colloidal Material sheared between 2 rapidly rotating close plates. Low efficiency & reduce the size of small proportion of particles Stabilizers added to control the size( gums, gelatin) Eg: collidal kaolin, zno Video 1……

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Ultrasonic generator: Dispersion achieved by high intensity UG at frequency more than 20,000 cycles/second stabilizers: surfactants Peptization: Aggregates to colloidal sized particles Removal of electrolytes Addition of surfactants Peptizing agents: glycerine, sugar, lactose

Electric arc : 

Electric arc Involves production of an electric arc within the liquid and Dispersion achieved by intense heat generated by the arc so some metal of the electrodes dispersed as vapor then condense to colloidal particles KOH - stabilizer.

3. Association colloids: : 

3. Association colloids: Certain molecules or ions termed amphiphile (surface active agent SAA) are characterized by two distinct regions of opposing solution affinities within the same molecules or ions.

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CMC – the concentration of the surfactant at which the micelles are formed is called as critical micellar concentration.

Kraft point : 

Kraft point Def: the temperature at which the solubility of surfactant is equal to the CMC . At this point, the conc. Of the surfactant is sufficient to form micelles. phenomena of enhancing solubility by forming micelles – MICELLAR SOLUBILIZATION.

Purification of colloidal solutions: : 

Purification of colloidal solutions:

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