Colloids
- 1. Colloids Prepared by , Mr. Snehal Patel Assistant Professor, Sumandeep Vidyapeeth, Vadodara, Gujarat, India.
- 2. Content • Definition • Application • Difference between molecular and Colloidal dispersion • Characteristics of dispersed phase • Classification of colloidal dispersion
- 3. Definition • A colloidal system is dispersion wherein dispersed particles (internal phase) are distributed uniformly in a dispersion medium (external phase). • The word colloid comes from a Greek word 'kolla', which means glue thus colloidal particles are glue like substances. • Colloidal system are defined as those polyphasic system. • Dimension of the dispersed phase measures between 10-100 A to a few micrometers. • Colloids can be made settle by the process of centrifugation.
- 6. Examples of colloids • Milk • Foam • Aerosol • Blood • Fog • Butter • Ice cream • etc
- 7. Application of colloids 1. Therapy: Some colloidal dispersion show better therapeutic action and are used in treatment. Silver colloid – germicidal Copper colloid – anticancer Mercury colloid – antisyphilis 2. Absorption and toxicity: • Colloidal sulfer shows better and faster absorption compared to a coarse dispersion of sulfer. • Complete absorption of sulfer from the colloidal dispersion results in high concentration in the blood, which often leads to toxicity.
- 8. Application of colloids 3. Solubility: Solubility of drug is improved by using colloidal systems containing surface active agents. 4. Stability: Dispersion of surface active agent (associated colloids) are used to improve the stability of drugs in liquid dosage forms. 5. Targetting of the drug to the specific organs: • Colloids are used in targeting the drug to specific body organs. • For example, drug entrapped liposomes are being preferentially take up by the liver and spleen. Other colloidal drug delivery systems include carrier systems such as liposomes, niosomes, nanoparticles and micro-emulsion.
- 9. Distinguish between molecular and colloidal dispersion Property Molecular Dispersion Colloidal Dispersion Size of particle Less than 1 nm 0.5mm to 1 nm Visibility Not visible even with electron microscope Visible with ultra microscope and electron microscope Scattering of light Does not scatter Scatter and shows tyndall effect Transport across semipermeable membrane Permeable Impermeable Settling Does not settle on ultracentrifugation Settle on ultracentrifugation Diffusion rate Rapid slow
- 10. Characteristics of Dispersed Phase 1. Particle size • Particle size influences the colour of the dispersion. • For eg: colloidal gold has red colour, while intermediate size is violet colour. The coarse dispersion of gold appears blue. 2. Particle shape • The shape of particle in dispersion depends on the method of preparation and affinity of the particles to the dispersion medium. • Shape also influences the colour of the dispersion. It is believed that spherical particle of gold is indicated by red colour, while disc like particle of gold gives blue colour.
- 11. Particle shape
- 12. 3. Surface area • As the size of the colloidal particles is of the order of a few micrometers, these particles possess enormous surface area, when compared to the coarse particles. • Their large surface area make them effective catalysts. • The larger surface area enhances the solubility of the drug particle. 4. Surface Charge • Colloidal particles possess charge on their surfaces. Negative Positive Acacia Gelatin Sulfur Bismuth Tragacanth Aluminium
- 13. • The charge on these particles and its environment in adispersion medium is shown in the figure. • The interior of these particles is electronically neutral, but the surface becomes charged. • The reason for the origin of the charge on the surface of particle is 1. Functional group –COOH present on the surface may get ionised. 2. Ions present in the medium may gets adsorbed onto the surface of the particles. Even in pure water either OH- or H+ ions may gets adsorbed to the surface of the particles.
- 14. • Surface charge provides valuable information regarding the stability of the colloids. Particles move continuously in random manner with collision with each other. • The like charge of the particles creates repulsion forces. During these collosions, particles remain as individual entities and distributed uniformly. Thus stability of colloids is attributed to surface charge.
- 15. Classification of colloidal dispersion 1. Lyophilic colloids 2. Lyophobic colloids 3. Associated colloids
- 17. Association colloids • Amphiphiles are the molecules or ions which have certain affinity for both polar and non polar solvents.
- 18. • In water, at low concentrations, surface active agent exist as individual monomer. • As the concentration increases, the monomer aggregate themselves over a narrow range of concentration. These aggregates are called as miscelles. • Each miscelle may contain around 50 monomers, and size may be around 50 Å.
- 19. Critical micelle concentration (CMC) • CMC is difined as the concentration range of of a surfactant at which miscelle starts forming.
- 20. Krafft Point, Kt • Krafft point is defined as the temperature at which the solubility of the surfactant is equal to the cmc.
- 21. Purification of Colloidal Dispersion • Dialysis • Electrodialysis • Ultrafiltration
- 22. Dialysis • It’s principle is that colloidal particles can not pass through a cellophane membrane while the ions of the electrolyte can pass through it. • The impurities slowly diffused out of the bag leaving behind pure colloidal solution. • The distilled water is changed frequently to avoid accumulation of the crystalloids otherwise they may start diffusing back into the bag. • Dialysis can be used for removing HCl from the ferric hydroxide sol
- 23. Electrodialysis • The process of dialysis is very slow. • The process is speeded up by application of electrical potential. • This is called electro dialysis. Application • Artificial kidney machine make use of electro dialysis.
- 24. Ultrafiltration