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COARSE DISPERSIONS NOTES, 1) EMULSIFYING AGENTS, An emulsifying agent (emulsifier) is a surface-active ingredient which adsorbs at the newly formed, oil–water interface during emulsion preparation, and it protects the newly formed droplets against, immediate re-coalescence., Emulsifying agents can be classified as:i) Natural:, Vegetable source: Gum acacia, tragacanth, agar, starch, pectin., Animal source: wool fat, egg yolk, gelatin., ii) Semi synthetic: Methyl cellulose, Na CMC, iii) Synthetic:, Anionic: Sodium Lauryl Sulphate, Cationic: Cetrimide, benzalkonium chloride., Non-ionic: Glyceryl ester- glyceryl monoesters etc., iv) Inorganic: Milk of magnesia, Mg oxide, Mg trioxide etc., v) Alcohols (polyoles): Carbowax, cholesterol and lecithin., , They can also be classified as:
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2) THEORIES OFEMULSIFICATION, There are 3 theories of emulsification:1) Monomolecular adsorption and film formation theory, 2) Multimolecular adsorption theory, 3) Solid particle adsorption theory, 1), , 2)
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3), , 3) EVALUATION TEST FOR STABILITY OF EMULSION, i) Globule size analysis, Microscopic evaluation of Globule size gives idea of stability of an emulsion., If the globule size are larger, it indicates the aggregation of globules and due to which, the emulsion is not stable., , ii) Centrifugation, The Emulsion is kept in centrifuge and then plot of Depth of Oil in centrifuge Vs Time (in seconds), is plotted., As the depth increases the stability is less., , iii) Viscosity:, Measured using Viscometers, , iv) Stress condition:
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Aging and temperature (Accelerated stability studies):, Helps in predicting the shelf life of emulsion., , 4) THEORY OF SEDIMENTATION IN SUSPENSION, Settling is a phenomenon which occurs in dispersed system where the dispersed particles settle to, the bottom of the container because of gravitational force., This occurs because the particles are too large to remain permanently suspended in the vehicle., Therefore suitable suspending agents are added to retard this process., , Theory of sedimentation: Stokes law, , V= Velocity of sedimentation, d= Diameter of particle, ρ1 and ρ2 =Density of particle and liquid, η = viscosity of liquid, g=gravitational const, Pharmaceutical suspension containing less than 2% (w/v) of solid follow Stoke’s Law., , 5) PHASE VOLUME RATIO
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6) STABILITY PROBLEMS IN EMULSION, , i) Flocculation, In this case, neighboring globules come closer to each other and form colonies in external phase., This aggregation of globules is not clearly visible., Uniform sized globules prevent flocculation. This can be achieved by proper size reduction, process., If the viscosity of external medium is increased, the globules become relatively immobile and, flocculation can be prevented., Flocs slowly move either upward or downward leading to creaming.
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ii) Creaming, Flocculation is due to interaction of attractive and repulsive force, where as creaming is due to, density differences in two phases., , Creaming can be prevented by:, *Reducing the particle size by homogenization., *Increasing the viscosity of external phase by adding the thickening agents., *Reducing the difference in densities between dispersed phase and dispersion medium., iii)
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Coalescence is observed due to:-Insufficient amount of emulsifying agent, -Altered partitioning of emulsifying agent, -Incompatibilities between emulsifying agents, iv) Breaking, This is indicated by complete separation of oil and aqueous phase., It is an irreversible process i.e. simple mixing fails to re-suspend the globules into a uniform, emulsion., In breaking, protective sheath around the globules is completely destroyed., , v) Phase inversion, Phase inversion means change in the type of emulsion i.e. o/w to w/o or vice versa, Reasons for phase inversion., *Addition of electrolyte., *Changing phase volume ratio., *Temperature change., *Changing the emulsifying agent.
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7) SEDIMENTATION VOLUME IN SUSPENSION, Sedimentation Volume (F), Sedimentation volume is the ratio of the ultimate volume of sediment (Vu) to the original volume, of suspension (Vo) before settling., , F = Vu / Vo, Where,, Vu = final or ultimate volume of sediment, Vo = original volume of suspension before settling, , F has values ranging from less than one to greater than one., When F < 1, , Vu < Vo, , When F =1 Vu = VoThe system (F =1) is said to be in flocculation equilibrium and show no, clear supernatant on standing., When F > 1 Vu > Vo Sediment volume is greater than the original volume due to the network of, flocs formed in the suspension and so loose and fluffy sediment and extra vehicle is needed, (added) to contain the sediment, , 8) CREAMING IN EMULSION AND HOW IT IS PREVENTED, Creaming
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Flocculation is due to interaction of attractive and repulsive force, where as creaming is due to, density differences in two phases., , Creaming can be prevented by:, *Reducing the particle size by homogenization., *Increasing the viscosity of external phase by adding the thickening agents., *Reducing the difference in densities between dispersed phase and dispersion medium., , 9) DISTINGUISH BETWEEN FLOCCULATED AND DEFLOCCULATED SYSTEM, Flocculated Suspensions, In flocculated suspension, formed flocs (loose aggregates) will cause increase in sedimentation rate, due to increase in size of sedimenting particles., Hence, flocculated suspensions sediment more rapidly., Deflocculated suspensions, In deflocculated suspension, individual particles are settling., Rate of sedimentation is slow , which prevents entrapping of liquid medium which makes it, difficult to re-disperse by agitation.This phenomenon called ‘caking’
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In deflocculated suspension larger particles settle fast and smaller remain in supernatant, liquid so supernatant appears cloudy.
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10) WETTING AGENTS, , Wetting phenomenon, Contact angle is the angle between liquid droplet and surface over which it spreads., Important action of wetting agent is to reduce the value of contact angle., , CLASSIFICATION OF WETTING AGENTS
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11)SIGNIFICANCE OF WETTING IN SUSPENSION, Wetting reduces the contact angle between liquid droplet and surface over which it spreads., Important action of wetting agent is to reduce the value of contact angle., , 12) CONTROLLED FLOCCULATION, Need of Controlled Flocculation, Assume the powder is properly wetted and dispersed.
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In order to prevent compact sediment (hard cake) we need controlled flocculation, Controlled Flocculation can be achieved through following methods:, 1)Effect of Electrolytes (ionic substance), 2) Effect of, , Surfactant, , 3) Effect of Polymer, , 1) Effect of electrolytes, It act as flocculating agents by reducing electrical barrier between particles and forming bridge, between adjacent particles, At low electrolyte conc --Repulsive force predominate, At high electrolyte conc -- Repulsive force reduce and cause coagulation, , Bismuth subnitrate suspension, Bismuth sub nitrate particles posses +ve charge, If we add monobasic potassium phosphate (KH2PO4) then positive zeta potential decrease to zero, because of adsorption of -ve phosphate ions then increase in negative direction, At certain +ve zeta potential, maximum flocculation occur
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2) Effect of, , Surfactant, , Concentration of (cationic/anionic) surfactant as flocculating agent is critical because, they act as wetting and deflocculating agent, Surfactant improve dispersion by reducing surface tension, Ionic surfactant (SLS) sometime cause flocculation, , 3) Effect of Polymer, Hydrophilic polymer act as protective colloids and flocculating agent., Chain of polymer adsorb on multiple particles, Ex. Xanthum gum increase sedimentation volume by polymer-bridging phenomenon for bismuth, sub-carbonate, , 13) CLASSIFY AND DESCRIBE TYPES OF EMULSIONS WITH EXAMPLE, Emulsions are classified as:i) o/w type: oil is the dispersed phase and water is the continuous phase., Eg: liquid paraffin emulsion, milk, ii) w/o: water is the dispersed phase and oil is the continuous phase, Eg: butter, cold cream
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iii) Multiple, emulsion:, Use for, subcutaneous and Intravenous injection., Sub-divided as:, a) o/w/o type, b) w/o/w type, , iv) Macro emulsion: particle size in the range of 0.1µm – 5µm, v) Micro emulsion: particle size in the range of 140 nm-5µm
