Colloidal Dispersions PDF

Colloidal Dispersion A system in which particles of colloidal size (1nm-0.5µm) are dispersed in a continuous Colloidal Dispersions...

Colloidal Dispersion A system in which particles of colloidal size (1nm-0.5µm) are dispersed in a continuous Colloidal Dispersions phase of a different composition Classes – Lyophilic – Lyophobic JHON RAPHAEL M. JIMENEZ, RPh, MS Lecturer – Association colloids Colloidal Dispersion Classes Colloidal Dispersion 1. Lyophilic Methods of Preparation – “solvent-loving” – Spontaneous 1. Condensation – Thermodynamically stable – Principle: small particles- (condensed)→colloidal particles 2. Lyophobic 2. Deflocculation/Dispersion – Principle: bigger particle-(broken down)→colloidal – “solvent-hating” particles – Nonspontaneous 3. Peptization – Thermodynamically unstable – Similar to the principle of salting-out 3. Association colloids – (+) electrolyte solution will cause the precipitation of – Preparation involves surfactants which can accumulate colloidal sized particles and form a micelle (colloidal sized particles)  Colloidal Dispersion Faraday-Tyndall Effect Properties: Optical § Faraday-Tyndall Effect üability to scatter or disperse light üE.g: foggy street Kinetic – Brownian motion colloidal particles appear as tiny points in constant motion when examined under an ultramicroscope – Diffusion spontaneous movement of particles from a region of higher concentration to one of lower concentration until equilibrium is achieved Colloidal Dispersion Coarse Dispersion Electric Particles are not uniform in size – Nerst Potential/Electrothermodynamic potential Particles undergo aggregation or clumping difference in potential between the actual surface of the particle and the electroneutral region of the Become heterogeneous with time dispersion – Zeta Potential/Electrokinetic Potential Particle size: >0.5µm difference in potential between the surface of the Eg: emulsions and suspensions tightly-bound layers and the electroneutral region of the dispersion Has more application in pharmacy (e.g ↓ zeta potential results to flocculation)  Coarse Dispersion Rate of Settling Rate of Settling 𝑑2𝑔 (𝜌1 − 𝜌2) 𝑆𝑒𝑑𝑖𝑚𝑒𝑛𝑡𝑎𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑒 = – Separation or creaming 18 𝜂 – Stoke’s Law: the rate of settling of the dispersed phase in the dispersing medium is a function of Where: d = particle diameter the particle size, dispersion phase viscosity, and difference in density between the dispersed phase g = acceleration due to gravity and the dispersion medium 𝜂 = viscosity of the dispersion medium 𝜌1 − 𝜌2 = difference between the density of the particles and the medium Suspensions Emulsions - Two-phase systems composed of solid - Heterogenous system consists of at least one material dispersed in an oily or aqueous liquid immiscible liquid that is intimately dispersed - Particles must be small (ngt 0.5 mm) in another, in the form of droplets - Not have a high particulate (dispersed phase) - Droplet diameter usually exceeds 0.1 µm concentration which can increase particle to - Unstable because the droplets of the dispersed liquid tend to coalesce to form large droplets until particle collisions which may cause all of the coalesced aggregation and instability - Addition of emulsifying agent prevents - Increase in viscosity of the dispersion medium coalescence and maintains integrity of individual decreases rate of settling droplets  Emulsions Coarse Dispersion Emulsifying agent Stability problems – Interfacial film formation of a surfactant around the – Phase inversions droplets in order to prevent direct contact of the liquid o/w → w/o or vice versa phase of the droplets – Electrostatic repulsion of similarly charged particles – Cracking total separation of two phases Creaming – Creaming – Reversible separation of layers upward or downward movement of internal phase of the emulsion Cracking – Sedimentation – Irreversible phase separation downward movement Phase inversion – Aggregation – Change of a/w to w/o and vice versa globules come together but do not fuse – Changes the consistency of emulsion and instability – Coalescence globules come together and fuse Coarse Dispersion Suspensions Deflocculated Flocculated Sedimentation Slower Faster rate Settling “hard cake” “loose cake”→ easily re- dispersed