User:Kuvad vikram/sandbox

KUVAD VIKRAMKUMAR.M.(THERAPY AREA SPECIALIST MERCK PHARMA)

'HE WAS TRAINING IN SINGAPORE ALL BIPHASIC LIQUID DOSAGE FORM AND OTHER HE WAS GOLD MEDALIST FROM SINGAPORE PHARMACY COUNCIL

3. Dispersed Systems Dispersed systems consist of particulate matter, known as the dispersed phase, distributed throughout a continuous or dispersion medium. The particulate matter, or dispersed phase, consists of particles that range from 1 nm to 0.5 mm (10–9 m to 5 x 10–7 m). Dispersed systems are classified as follows: • Molecular dispersions: <1 nm, invisible under electron microscopy (EM). Examples are oxygen molecules, ions, and glucose. • Colloidal dispersions: 1 nm to 0.5 mm, visible under EM. Examples are colloidal silver sols and natural and synthetic polymers. • Coarse dispersions: larger than 0.5 mm, visible under light microscopy. Examples are grains of sand, emulsions, suspensions, and red blood cells. Types of Colloidal Systems Colloidal systems are classified as lyophilic or lyophobic. Their association is based on the interaction of the particles or molecules of the dispersed phase with the molecules of the dispersion medium. Lyophilic colloids Systems containing colloidal particles that interact with the dispersion medium are referred to as lyophilic colloids. Because of their affinity for the dispersion medium, such materials form colloidal dispersions with relative ease. For example, the dissolution of acacia or gelatin in water or celluloid in amyl acetate leads to the formation of a solution. Most lyophilic colloids are polymers (eg, gelatin, acacia, povidone, albumin, rubber, and polystyrene). Lyophobic colloids Lyophobic colloids, or inorganic particles dispersed in water, are composed of materials that have little attraction, if any, for the dispersion medium. Lyophobic colloids are intrinsically unstable and irreversible. Association colloids Association (referring to amphiphilic colloids) colloids are formed by the grouping or association of amphiphiles, ie, molecules that exhibit both lyophilic and lyophobic properties. At low concentrations, amphiphiles exist separately and do not form a colloid. At higher concentrations, aggregation occurs at around 50 or more monomers, which induces micelle formation. As with lyophilic colloids, formation of association colloids is spontaneous, provided that the concentration of the amphiphile in solution exceeds the CMC. Zeta Potential and Its Effect on Colloidal Stability Zeta (ζ) potential is defined as the difference in potential between the surface of the tightly bound layer (shear plane) and the electroneutral region of the solution. The ζ potential governs the degree of repulsion between adjacent, similarly charged, dispersed particles. If ζ potential is reduced below a certain value, the attractive forces exceed the repulsive forces, and the particles come together. This phenomenon is known as flocculation. Stabilization is accomplished by providing the dispersed particles with an electric charge and a protective solvent sheath surrounding each particle to prevent mutual adherence due to collision. This second effect is significant only in the case of lyophilic colloids. Lyophilic and association colloids are thermodynamically stable and exist in a true solution so that the system constitutes a single phase. In contrast, lyophobic colloids are thermodynamically unstable, but can be stabilized by preventing aggregation/coagulation by providing the dispersed particles with an electric charge, which can prevent coagulation by repulsion.

by kuvad vikram