PS 8 H

• interfacial phenomena


  the interactions at the surface between two liquids (immiscible) or a liquid and a gas. the molecules at the surface of a solid or liquid are subjected to different forces and behave differently from the bulk. the bulk are attracted towards each other in all directions, net force is 0. The surface molecules are not pulled up by molecules above them (as there are none) creating surface tension and a meniscus. thus water can support light loads and form spherical droplets.
• contact angle


  droplets resting on a surface form a contact angle (theta), the size of which depends on the physiochemical properties of the liquid and the surface. the larger the angle the more hydrophobic (hydrophilic less than 90 degrees)
• wetting


  the ability of a liquid on a surface to spread out as a film rather than remain a droplet. total wetting, a thin film. partial wetting is slightly droplet. a wetting agent can be added to assist wetting. no wetting, the droplet will roll off.
• changing surface tension


  organics, surfactants decrease. electroyltes (salt) will increase
• meniscus


  where the container and liquid meet, adhesion pulls the liquid up and cohesion pulls the liquid together. the meniscus is higher depending on diameter of tube, smaller tube, the more adhesion to pull the liquid up
• emulsion


  mixture of aqueous and non-aqueous phase of non-soluble liquids in droplets. if oil is whisked rapidly droplets of oil will form in the water but the solution will eventually settle into two layers. however if these droplets are established by other ingredients they will remain stable.
• types of emulsions


  o/w primary(continuous phase is water, dispersed phase is oil.) milk/cream, w/o butter, o/w/o secondary (oil droplets surrounded by water globule surrounded by oil phase), w/o/w (water droplets surrounded by oil globule surrounded by water phase). secondary can be used for delayed release of components
• emulsion size


  macro, micro and nano. the smaller the droplets the clearer the solution appears, the larger droplets are opaque solutions
• distinguishing o/w and w/o emulsions

  add oil or water to the emulsion if it disperses quickly it is the same as the external phase, if not it is the internal phase. put a few drops on filter paper. o/w emulsion will spread quickly whereas a w/o emulsion will spread slowly. add a few drops of water-soluble dye and see how it spreads. o/w conduct while w/o don't
• emulsion uses


  oral - called emulsions, can disguise tastes and increase oral availability, can include wax dissolved in oil (laxatives, cyclosporin). injectables - (diazepam, IV total parenteral nutrition) topical emulsions - o/w or w/o, lotions or creams (antiseptic creams, sunscreens)
• o/w vs w/o


  o/w - orally, topically or parenterally. non-greasy. easily removed from skin, cosmetically acceptable, conduct electricity. w/o - not oral or parenterally, greasy, not easy to remove from skin, not cosmetically acceptable, do not conduct, have occlusive effect by hydrating stratum corneum and inhibiting evaporation of sweat
• advantges of emulsions


  can aid drug delivery to patients with swallowing difficulties, parenteral nutrition, can deliver hydrophobic drugs with poor water solubility, can deliver two incompatible drugs, can mask taste, can add flavourings and sweeteners to aq phase, can reduce dermal irritant action of drugs
• disadvantages of emulsions


  thermodynamically unstable at high or low temps, difficult to manufacture and formulate, easy to contaminate, potential degradation of emulsifying agent can lead to cracking, need to be shaken before use, measuring device required, easy to make dosing errors, bulky to transport and store
• physical instability of emulsions

  coalescence - droplets join together to form larger droplets. flocculation - clusters of droplets. creaming - droplets float to the surface and foam on the top. breaking - two layers completely separate
• phase inversion


  o/w becomes w/o if there are similar amounts of each product
• steps to make emulsion


  water to oil + emulsifier (w/o) or oil to water + emulsifier (o/w). depends on the nature of the emulsifier, the ratio of phase volume and temp. may add electrolytes and other substances, flavours etc.
• emulsifying agents


  possess a degree of affinity for polar and non-polar liquids and act as a bridge between the two phases reducing the interfacial tension. common agents: surface active agents (surfactants) that form a monomolecular layer/film around droplets (oleic acid, anionic, cationic and nonionic surfactants). hydrophilic colloids that form a multi-molecular layer around the droplets (agar gum, tragacanth). finely divided particles that form a particulate film around the droplets (Veegum, hectorite)
• hlb system


  hydrophilic-lipophilic balance. used to measure if an emuslfing agent if more hydrophilic or lipophilic. the more hydrophilic the bigger the head, the more lipophilic the longer the tail. 1-40 scale. 1 is lipophilic, 40 is hydrophilic. o/w (8-16) w/o (3-6). examples (sodium lauryl sulfate 40), acacia gum (12), oleic acid (1). low HLB for w/o, high HLB for o/w.
• blended emulsifying agents


  emulsions often contain more than one agent, and a weighted mean is calculated to achieve the desired HLB
• excipients in emulsions


  preservatives - ethanol, benzoic acid, and parabens. antioixidants - vitamin c and e, sulfites. viscosity enhancers - gums, gelatin.
• manufacture and packaging of emulsions

  mixing and warming if required of ingredients in order or most soluble, bring the two phases together at the sample temp. the gradual addition of the disperse phase to the external phase with constant rapid agitation (stirring, beating or ultrasonication) to ensure globule size reduction and dispersion and to produce the emulsion. cooling if needed. QC and packaging (bottles, vials, ampoules, clear or opaque)
• extemp methods


  continental dry gum - emulsifying agent mixed with oil. oil + emulsifier mixed with aqueous phase. wet gum -emulsifying agent mixed with the aqueous phase, slow drop-by-drop addition of oil to aq phase + emulsifier and blending. potential problems with both: creaming, cracking and phase inversion.