colloids part 3

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Information about colloids part 3

Published on February 19, 2014

Author: jayaraj2775


PowerPoint Presentation: COLLOIDS PART 3 PowerPoint Presentation: PART 3 PowerPoint Presentation:  Purification of sols may be accomplished by the following methods. (a) Dialysis (b) Electro dialysis (c) Ultrafiltration Dialysis In this process, ions or molecules are removed from a Colloidal dispersion by diffusion through a semi permeable membrane . A semi permeable membrane of collodion has very fine Pores, these pores permit the passage of ions (sodium and chloride) and small molecules but prevent the passage of colloidal particles, owing to their bigger size. Dialysis: Dialysis PowerPoint Presentation:  Construction & working : The semi permeable membrane is fixed tightly to one end of a hollow glass tube. The colloidal dispersion is placed in the glass tube and is suspended in a vessel through which fresh water is continuously passed. Ions and other 'molecules diffuse (impurities) out of the bag into water rapidly. In this way, purification of colloidal dispersion may be achieved . 2. Electro dialysis : 2. Electro dialysis The principle of electro dialysis is similar to dialysis. Diffusion of ions or molecules is enhanced by applying a potential difference across the membrane. This method is called electro dialysis . Nonionic impurities cannot be separated by this method . PowerPoint Presentation: 3. Ultra filtration The colloidal dispersion is filtered through ultra filters to remove all electrolytes. Colloidal dispersion can pass through an ordinary filter paper, because the pore size of filter paper is large . (allows the passage of even colloids) If this filter paper is impregnated with Collodions , the pore size reduces. (only the impurities can pass through the filters). Such modified filter papers are Called ultra filters. Ultra filtration: Ultra filtration Properties of colloids:  1. Optical Properties 2. Electrical Properties 3. Kinetic Properties WHY? Colloidal Silver – Germicidal Colloidal copper – Anticancer Colloidal Mercury – Antisyphilis Properties of colloids 1. Optical Properties : The study of optical properties of colloids helps in obtaining the information on the size, shape, structure and molecular weights of the colloids. The interaction of colloidal particles with the light is studied under their optical properties. 1. Optical Properties Methods available to study optical properties of colloids: 1. Light Microscope The light microscope uses visible light (400nm -800nm) and above as its source or radiation. Particle sizes of lower range (less than 400nm) are not well detected. Hence the light microscope is not much useful in studying the structure and size of colloids. Methods available to study optical properties of colloids Optical Properties:  When an intense, narrow beam of light is passed through the dispersion of colloids, it scatter more light. The source of light and resolving power of the optical system determine the precision and usefulness of their structure and size. Tyndall effect is observed due to the interaction of particle with light . When a beam of light strikes the particle, it polarizes the atoms and molecules in it and induces dipoles and thereby emits light , thus light scatters in all direction. This effect is called as Tyndall effect. Optical Properties Optical Properties: 2.Ultra microscope (Dark Field Microscope) The working principle of the instrument is that the light scattered by the particles is viewed at right angles to the incident light . The colloidal particles appear as spots of light against the dark back ground. Ultra microscope is used to study the charges of the particles Optical Properties Optical Properties: 3. Electron Microscope (TEM, SEM) The colloidal particle size, shape and structure can be determined using an electron Microscope . Electron microscope has high resolution power. (Smaller the wavelength of the radiation beam the greater the resolving power) Optical Properties PowerPoint Presentation: 4.Turbidity This method is used to estimate the concentration of dispersed Particles and molecular weight of the solute. The turbidity produced by the colloids can be measured by spectrophotometer and Nephlometer. Spectrophotometer : :  It measures the intensity of the transmitted light in the direction of the incident light. The relative intensity of transmitted light is correlated to the turbidity Principle: If the dispersed phase has high solid, then more light will be scattered and the light transmitted will have less intensity. Spectrophotometer : Nephlometer: Nephlometer Measures & indicates intensity of scattered light When the amount of dispersed phase is low the intensity of scattered light is measured at right angles to the direction of incident light. Optical Properties….: 5. Light Scattering Molecular weight of polymers and micelles can be measured by this method. Molecular weight of proteins, polymers, association colloid and Lyophobic sols can also be studied by this method. Principle: Light source having a wavelength, higher than the dimension of the particle is used. Here the turbidity is measured from the scattered light by viewing at right angles. Optical Properties …. Kinetic Properties of colloids and their applications in pharmacy.:  The study of kinetic properties of colloidal dispersions is important to the pharmacist in (a) Predicting the stability of system. (b) Determining the molecular weight of particles. (c) Studying the transport kinetics of colloidal particles. Kinetic Properties of colloids and their applications in pharmacy. PowerPoint Presentation:  1. Brownian Motion 2. Diffusion 3. Sedimentation 4. Viscosity Kinetic Properties of colloids 1.Brownian Motion-Kinetic Properties :  The colloidal particles exhibit Brownian motion under light microscope. Colloidal particles do not settle because of their small size and continues Motion (Brownian motion). Thermal energy keeps particles in motion . They collide with each other and with the walls of the container. These collisions change the direction and velocity of particles. These molecular collisions keep particles under continuous and random motion. Brownian motion can be decreased or stopped by increasing the viscosity of the medium. 1.Brownian Motion-Kinetic Properties 2. Diffusion Kinetic Properties :  Since the size of colloidal particles is small, these can diffuse through membranes such as porous plug. Diffusion occurs spontaneously. This property helps in the estimation of molecular weight of polymers such as egg albumin and hemoglobin . Diffusion is a direct result of Brownian motion. Diffusion can be expressed by Fick's first law. Diffusion coefficient of the polymer is determined by Fick's first law. 2. Diffusion Kinetic Properties 3. Sedimentation: Kinetic Properties :  Forced sedimentation (Ultracentrifuge) is used to determine the molecular weight of the polymers by preparing as colloidal dispersion. Molecular weight of antibiotic and micelles are also estimated by this method . 3. Sedimentation: Kinetic Properties Kinetic Properties Equation used in the determination of molecular weight polymers.: Kinetic Properties Equation used in the determination of molecular weight polymers. Where D = diffusion coefficient of the polymer R = molar gas constant T = absolute temperature(293 ◦ K) = viscosity of dispersion medium N = Avogadro's number M = molecular weight of the polymer = partial specific volume of the particles 4. Viscosity - Kinetic Properties :  The viscosity of a colloidal dispersion is affected by a variety of factors like affinity of particles to the medium . Spherical particles impart relatively low viscosities , Affinity between the particle and medium is low then it shows low viscosity. Higher the M.W, the greater the viscosity and by measuring the viscosity the M.W of polymer can be determined. 4. Viscosity - Kinetic Properties Electric Properties: Surface charges – Zeta potential: The dispersed particles of the colloid possess a charge on their surfaces. The distribution of ions in the environment of a charged particle is explained by the concept of the electrical double layer. When particles move, this shell of the double layer also moves along with the particle . The electrical potential in the plane of shear of the charged particle is called as zeta potential. Electric Properties Electric Properties :  Zeta potential has an application in predicting the stability of the dispersion system. Zeta potential can be determined using the method of electrophoresis. Measured in mV. Electrophoresis: The principle of electrophoresis is used to determine the sign and magnitude of zeta potential. Electrophoresis involves the movement of a charged particle through a Liquid , under the influence of an applied potential difference. An electrophoresis cell is fitted with two electrodes . The dispersion is introduced into the cell. When a potential is applied across the electrodes, particles migrate towards oppositely charge electrodes. Electric Properties Electrophoresis cell: Electrophoresis cell Electrophoresis:  If the particles move towards anode , the charge on the particle is negative. If particles move towards cathode, the charge on the particles is positive. Thus the sign of zeta potential can be determined. The rate of migration is a function of the charge on a particle . Ultra microscope is used to observe the migration of particles. As the potential gradient across the electrodes increases, the velocity of migration of a particle increases. Electrophoresis

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