colloids part 2

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TYPES OF COLLOIDAL SYSTEMS Classified on the basis of the interaction of the particles , molecules, or ions of the dispersed phase with the molecules of the dispersion medium. Classified into three a) Lyophilic b) Lyophobic c) Association colloids


TYPES OF COLLOIDAL SYSTEMS 1.Lyophilic colloids: (solvent loving) Lyophilic colloids Colloidal particles interact to an appreciable extent with the mol ecules 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. The dispersion medium forms a sheath around the colloidal particles and solvates. This makes the dispersion thermodynamically stable . These, dispersions are reversible. (These colloidal particles can be reconstituted after the purification step).


TYPES OF COLLOIDAL SYSTEMS 2. . L yophobic colloids : (solvent hating). These are dispersions in which very little attraction or no attraction ( Lyo means solvent, phobic means hating) is possible between the dispersed phase and dispersion Medium. The solvent sheath surrounding the particle is absent. The like charges on particles keep them away from each other and remain uniformly dispersed on account of repulsive. These dispersions are thermodynamically unstable . In general, the dispersed phase consists of inorganic particles and the medium is water . Ex : Gold, silver, sulfur, arsenous sulfide and silver iodide in water.


TYPES OF COLLOIDAL SYSTEMS 3. .Association colloids : Association colloids are other wise called as amphiphilic colloids. Eg - Surfactants or surface active agents – Sodium lauryl Sulphate. (SLS) Cetyl trimethyl bromide (CTMB) Polyoxyethylene lauryl ether (POLE) In this the dispersed phase molecules or ions have certain affinity for the disperse medium.

Behavior of surfactant molecules in a polar and non polar media::

Behavior of surfactant molecules in a polar and non polar media: In water, at low concentrations ,surface active agents exist individually as monomers , which are sub colloidal in size. As the concentration increases , the monomers aggregate themselves and these aggregates are called as micelles . This size falls into the Colloidal range and are designated as colloidal systems .

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Fig: In the micelles, the nonpolar chain is designated as the tail and polar portion is indicated by head. Structure of micelle

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Spherical micelle in aqueous media Reversed micelle in non aqueous media Shape of micelles

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Shape of micelles Laminar micelle formed at higher amphiphile concentration in aqueous media

Critical micelle concentration:

Critical micelle concentration Defined as the concentration range of a surfactant at which micelles start forming . Unit is w/w, w/v percent, moles/liter, etc. Below CMC surface active agents preferentially get adsorbed at air water interface . As the concentration of surfactant increases, molecules get accumulate progressively at the interface . .

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In this process, at one particular concentration, the interface gets saturated , while the bulk phase is saturated with monomers

Behavior of surfactants in polar and nonpolar solvents…:

Behavior of surfactants in polar and nonpolar solvents…


Cmc…. In the bulk of the solution, both monomers and micelles are in dynamic equilibrium . This concentration is called as CMC . Beyond CMC , any further addition of surface active agents enhances the formation of micelles only .

Applications of miceller solubilization….:

Applications of miceller solubilization…. Poorly water-soluble drugs are normally solubilised in aqueous solutions by employing association colloids. Surface active agents at and above CMC form micelles. In aqueous dispersions these micelles are spherical in shape and contain a hydrophobic interior and a hydrophilic surface . Hydrophobic pockets inside micelles offer an environment for solubilization poorly water soluble drugs. This phenomenon is called as miceller solubilization.

Miceller solubilization….:

Miceller solubilization…. Eg: Solubilised systems containing volatile oils (peppermint oil), coal tar materials, Phenobarbital, sulfonamides and vitamins. Cresol with soap solution – the solubility of cresol in water is 2% , but it is increased to 50% by miceller solubilization.

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Preparation of colloids: A) Dispersion methods:(size reduction) 1) Ultrasonic generator 2) Electric arc. 3) Colloid mill. B) Condensation methods: 1) Addition of non-solvent 2) Chemical reaction. Preparation and purification of colloids

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1.Ultrasonic generator: Dispersion achieved by high intensity UG at frequency more than 20,000 cycles/second stabilizers: surfactants 2.Peptization: Aggregates to colloidal sized particles Removal of electrolytes Addition of surfactants Peptizing agents: glycerine, sugar, lactose Addition of surfactant Removal of electrolytes colloids

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Colloidal mill coarse to colloidal material sheared between two 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 3.Colloidal mill

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4.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.

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