EMULSION AND SUSPENSION

Includes introduction , mechanisms , theories , applications with examples

1. EMULSION AND SUSPENSION PRESENTED BY SAKSHI SINGH MODERN PHARMACEUTICS (MPH103

2.                 EMULSIONS                       

3. INTRODUCTION An emulsion is a dispersion in which the dispersed phase is composed of small globules of a liquid distributed throughout a vehicle in which it is immiscible.  The stability against drop coalescence is provided by the presence of a small amount of a third component, so-called emulsifier, which is in general a surfactent-agent or surfactant, that adsorbs at the drop interface and produces some inter drop repulsion according to a variety of static and dynamic phenomena

4. Classification of emulsions : Based on dispersed phase  Oil in Water (O/W): Oil droplets dispersed in water  Water in Oil (W/O): Water droplets dispersed in oil    Based on size of liquid drople t s  0.2 – 50 mm Macroemulsions (Kinetically Stable)  0.01 – 0.2 mm Microemulsions (Thermodynamically Stable)

5. Theories of Emulsification:   Surface Tension Theory Oriented-Wedge Theory  Interfacial film theory Charge repulsion theory Steric repulsion theory

6. SURFACE TENSION THEORY  According to the surface tension theory of emulsification, the emulsifying agents cause a reduction in the interfacial tension of the two immiscible liquids, reducing the repellent force between the liquids and withdrawing the attraction of liquids for their own molecules. In this way, the surfactants convert large globules into small ones and avoid small globules from coalescing into large ones.   In this way, the surfactants convert large globules into small ones and avoid small globules from coalescing into large ones.

7. ORIENTED-WEDGE THEORY This theory deals with formation of monomolecular layers of emulsifying agent curved around a droplet of the internal phase of the emulsion. Example   In a system containing two immiscible liquids, emulsifying agents would be preferentially soluble in one of the phases and would be embeded in that phase. A. Emulsifier molecules oriented at interface

8. INTERFACIAL FILM THEORY  When two immiscible liquids come in contact, the force causing each liquid to resist breakage is known as interfacial tension. When a high interfacial tension existed between two liquids emulsification is difficult, and if the tension could be reduced emulsification facilitated.   The explanation that in oil in water dispersion, the interfacial tension is so great that when two globules of dispersed phase approach each other it withdraws the liquid from between them, with the result they coalesce. When the interfacial tension is greatly reduced by the addition of emulsifier the globules remain separate.

9. CHARGE REPULSION THEORY This theory of emulsions says that the fine globules of dispersed phase are separated due to the repulsive forces developed as a result of the nature of emulsifying agent (anionic or cationic) or by adsorbing ions from the dispersion medium. Charge develops on the surface of oil globules (o/w) is great enough to cause repulsion between droplets. The electrical barrier to prevent coalescence of the oil droplets and allow the oil phase to remain in droplet form, uniformly dispersed in continuous water phase.

10. STERIC REPULSION THEORY This theory says that the repulsion develops between the water droplets due to the long hydrocarbon chains of emulsifying agent which has been adsorbed on their surface. This repulsion is called d steric repulsion, preventing the contact or coalescence of water droplets.  theory can explain the process of emulsification only in w/o type of emulsion. 

11. EMULSIFYING AGENT 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 recoalescence. Pharmaceutically acceptable emulsifiers must also :   be stable .   be compatible with other ingredients .  be non – toxic .   possess little odor , taste , or color .   not interfere with the stability of efficacy of the active agent .

12. EXAMPLES OF EMULSIFYING AGENTS 1 ) Carbohydrate Materials: - Acacia, Tragacanth, Agar, Pectin. o/w emulsion. „ 2) Protein Substances: -Gelatin, Egg yolk, Caesin o/w emulsion.  3) High Molecular Weight Alcohols: - Stearyl Alcohol, Cetyl Alcohol, Glyceryl Mono stearate o/w emulsion, cholesterol w/o emulsion.

13. MECHANISM OF EMULSION •The increase in the energy of an emulsion compared to the nonemulsified components is equal to ∆W. This amount of energy can be considered as a measure of the thermodynamic instability of an emulsion                                                            D W = g D A  ∆W is the free energy of the interface and corresponds to the reversible work brought permanently into the system during the emulsification process . This makes an emulsion very prone to coalescence processes which lead to a decrease in ∆A and subsequently in ∆W. The conclusion is straightforward that ultimate stability against coalescence processes is only achieved if s approaches zero

14. TEST FOR IDENTIFICATION Dilution test : emulsion can be diluted only with external phase  Dye test: water or oil soluble dyes  CoCl 2/filter paper test: filter paper impregnated with CoCl 2 and dried (blue) changes to pink when o/w emulsion is added  Fluorescence : some oils fluoresce under UV light    Conductivity : for ionic o/w emulsions (o/w emulsions conduct electric current)

15. APPLICATION OF EMULSION In the metallurgical processes, the concentration of ore by forth floatation process is based upon the treatment of the powdered ore with oil emulsion. The valuable particles of the ore form foam which comes to the surface and is skimmed off.  Asphalt emulsified in water is used for building roads without the necessity of melting the asphalt.  Milk which is an important constituent of our diet is en emulsion of liquid fats in water.  Several oily drugs are prepared in the form of emulsions.  The cleansing action of ordinary soap for washing clothes, crockery etc. is based upon the formation of oil-in-water emulsion.

16. SUSPENSIONS

17. INTRODUCTION A suspension is  a heterogeneous mixture in which some of the particles settle out of the mixture upon standing . ... The particles in a suspension are far larger than those of a solution and thus gravity is able to pull them down out of the dispersion medium (water). PROPERTIES: - Heterogenous biphasic dosage form  solid is dispersed in liquid medium. Dispersed phase, dispersion medium  -Rapid settling  Easily redispersible ,pourable  if parenteral—flow through syringe needle  -if external---spread easily  -Pleasing in colour , odour , appearance.

18. CLASSIFICATION OF SUSPENSIONS Based On General Classes  Oral suspension  Externally applied suspension  Parenteral suspension    Based On Proportion Of Solid Particle s Dilute suspension (2 to10%w/v solid)  Concentrated suspension (50%w/v solid)   Based On Electrokinetic Nature Of Solid Particles  Flocculated suspension  Deflocculated suspension    Based On Size Of Solid Particles  Colloidal suspension (< 1 micron)  Coarse suspension (>1 micron) Nano suspension (10 ng)

19. THEORY OF SUSPENSION Sedimentation Behaviour   Sedimentation means settling of particle or floccules occur under gravitational force in liquid dosage form.  Theory of Sedimentation   The factors affecting the rate of sedimentation of a particle are described in Stoke’s equation                      

20. STOKES EQUATION T h e basic consequences of the stokes equation are that the rate of fall of a suspended particle in a vehicle of a given density is greater for larger particles than it is for smaller particles. Also the greater the difference in density between the particles and the vehicle, the greater will be the rate of sedimentation. Increasing the viscosity of the dispersion medium will reduce the rate o sedimentation. Thus decrease in the rate of sedimentation of particles in a suspension may be achieved by reducing the size of the dispersed particles and by increasing the density and viscosity of the dispersion/continuous phase.

21. SUSPENDING AGENTS Suspending agents are substances that are used to keep finely divided insoluble materials suspended in a liquid media by preventing there agglomeration (coming together) and by imparting viscosity to the dispersion media so that the particles settle more slowly NATURAL AGENTS This class consists of those from.  . Animal source eg Gelatine   .Plant source eg. Accacia, Tragacanth, Starch, sea weed (Alginates)' . mineral sources.eg Bentonite, Kaoline 2.  SEMI-SYNTHETIC AGENTS  These consist of substituted cellulos (minerals) eg. Hydroxyethylcellulose , Sodium Carboxymethylcellulose , methylcellulose, Microcrystalline cellulose

22. Flocculation is a condition which occurs as a result of the lowering of electrical forces of repulsion in a dispersed system , so that the force of attraction predominate. Systems under this condition reduced repulsive forces the dispersed particles to approach each other more closely and form aggregates known as flocs  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. The Sedimentation Behavior of Flocculated and Deflocculated Suspensions:  FLOCCULATED SUSPENSION

23. A deflocculated suspension is one in which the electrical repulsive forces between particles exceeds the attractive forces, the particles are kept apart as individuals affected only by the suspending vehicle. Even when brought together by random motion, they resist collision due to the high surface tension.   In deflocculated suspension, individual particles are settling, so rate of sedimentation is slow which prevents entrapping of liquid medium which makes it difficult to re-disperse by agitation.  This phenomenon also called ‘cracking’ or‘claying ’.   In deflocculated suspension,smaller particles settle slowly and therefore remaining supernatant liquid so supernatant appears cloudy and has a pleasing granular appearance whereby in flocculated suspension, even the smallest particles are involved in flocs, so the supernatant does not appear cloudy . DEFLOCCULATED SUSPENSION

24. APPLICATION OF SUSPENSION Suspension can be formulated for parentral application in order to control rate of drug absorption, E.g. penicillin procaine   Vaccines as a immunizing agent are often formulated as suspension.E.g . Cholera vaccine   X-ray contrast agent are also formulated as suspension. E.g. Barium sulphate for examination of alimentary tract  If the drug is unstable when in contact with the vehicle, suspensions should be prepared immediately prior to handing out to the patient in order to reduce the amount time that the drug particles are in contact with the dispersion medium. Eg Amoxicilin suspension Lotions containing insoluble solids are formulated to leave a thin coating of medicament on the skin. As the vehicle evaporates, it gives a cooling effect and leaves the solid behind.eg calamine lotion and sulphur lotion compound.