Industrial Chemistry Part VI Principles Emulsions 2011

Emulsions Administration Oral administration: Is a route of administration where a substance is taken through the mouth. 2) Topical administration: Topical emulsions are creams The Consistency of Emulsions A) Internal phase volume to external phase volume ratio B) In which phase ingredients solidify C) What ingredients are solidifying

Methods of Preparation of Emulsions: 1) Continental or Dry Gum Method: "4:2:1" Method and 4 parts (volumes) of oil 2 parts of water 1 part of gum. The continental method is used to prepare the initial or primary emulsion from oil, water, and a hydrocolloid or "gum" type emulsifier (usually acacia). The primary emulsion, or emulsion nucleus, is formed from 4 parts oil, 2 parts water, and 1 part emulsifier. The 4 parts oil and 1 part emulsifier represent their total amounts for the final emulsion. In a mortar, the 1 part gum is crushed with the 4 parts oil until the powder is thoroughly wetted; then the 2 parts water are added all at once, and the mixture is vigorously and continually triturated until the primary emulsion formed is creamy white and produces a "crackling" sound as it is triturated (usually 3-4 minutes). Additional water or aqueous solutions may be incorporated after the primary emulsion is formed. Solid substances (e.g., active ingredients, preservatives, color, flavors) are generally dissolved and added as a solution to the primary emulsion. Oil soluble substance, in small amounts, may be incorporated directly into the primary emulsion. Any substance which might reduce the physical stability of the emulsion, such as alcohol (which may precipitate the gum) should be added as near to the end of the process as possible to avoid breaking the emulsion. When all agents have been incorporated, the emulsion should be transferred to a calibrated vessel, brought to final volume with water, then homogenized or blended to ensure uniform distribution of ingredients

2) English or wet Gum Method: 4 parts (volumes) of oil 2 parts of water 1 part of gum In this method, the proportions of oil, water, and emulsifier are the same (4:2:1), but the order and techniques of mixing are different. The 1 part gum is triturated with 2 parts water to form a mucilage; then the 4 parts oil is added slowly, in portions, while triturating. After all the oil is added, the mixture is triturated for several minutes to form the primary emulsion. Then other ingredients may be added as in the continental method. Generally speaking, the English method is more difficult to perform successfully, especially with more viscous oils, but may result in a more stable emulsion.

3) Bottle or Forbes Bottle Method: useful for extemporaneous preparation of emulsion from volatile oils or oleaginous substance of low viscosity. powdered acacia + Dry bottle 2 parts of oil This method is not suitable for viscous oils (i.e. high viscosity oil).

This method may be used to prepare emulsions of volatile oils, or oleaginous substances of very low viscosities. It is not suitable for very viscous oils since they cannot be sufficiently agitated in a bottle. This method is a variation of the dry gum method. One part powdered acacia (or other gum) is placed in a dry bottle and four parts oil are added. The bottle is capped and thoroughly shaken. To this, the required volume of water is added all at once, and the mixture is shaken thoroughly until the primary emulsion forms. It is important to minimize the initial amount of time the gum and oil are mixed. The gum will tend to imbibe the oil, and will become more waterproof. It is also effective in preparing an olive oil and lime water emulsion, which is self-emulsifying. In the case of lime water and olive oil, equal parts of lime water and olive oil are added to the bottle and shaken. No emulsifying agent is used, but one is formed "in situ" following a chemical interaction between the components. What emulsifying agent is formed?

Beaker Method When synthetic or non-gum emulsifiers are used, the proportions given in the previous methods become meaningless. The most soluble components. A appropriate method for preparing emulsions from surfactants or other non-gum emulsifiers is to begin by dividing components into water soluble and oil ll oil soluble components are dissolved in the oily phase in one beaker and all water soluble components are dissolved in the water in a separate beaker. Oleaginous components are melted and both phases are heated to approximately 70°C over a water bath. The internal phase is then added to the external phase with stirring until the product reaches room temperature. The mixing of such emulsions can be carried out in a beaker, mortar, or blender; or, in the case of creams and ointments, in the jar in which they will be dispensed.

Emulsion Type and Means of Detection Dilution Test based on the solubility of external phase of emulsion. - o/w emulsion can be diluted with water. - w/o emulsion can be diluted with oil

Conductivity Test water is good conductor of electricity whereas oil is non-conductor. Therefore, continuous phase of water runs electricity more than continuous phase of oil. Bulb glows with O/W Bulb doesn’t glow with W/O

Dye-Solubility Test Water-soluble dye will dissolve in the aqueous phase. Oil-soluble dye will dissolve in the oil phase.

Fluorescence test oils give fluorescence under UV light, while water doesn’t. Therefore, O/W emulsion shows spotty pattern while W/O emulsion fluoresces.

Theories of Emulsification: 1) Surface Tension Theory: - lowering of interfacial tension. 2) Oriented-Wedge Theory: - mono molecular layers of emulsifying agents are curved around a droplet of the internal phase of the emulsion. 3) Interfacial film theory: - A film of emulsifying agent prevents the contact and coslescing of the dispersed phase.

How to control emulsion type during formulation? 1) Volume of internal and external phases controls the type of emulsion The smaller volume will be for the internal phase and the larger volume will be for external phase. In some cases, internal phases can be more than 50% of the total volume. An O/W emulsion is generally formed if the aqueous phase constitutes > 45% of the total weight, and a hydrophilic emulsifier is used W/O emulsions are generally formed if the aqueous phase constitutes < 45% of the total weight and an lipophilic emulsifier is used.

2) Dominance of polar and non-polar characteristic of emulsifying agents (relative solubility of emulsifying agent in water and oil) Dominance of polar part results in formation of o/w emulsion and dominance of non-polar part results in formation of w/o emulsion. Note that polar groups are better barriers than non-polar; therefore, o/w emulsion can be prepared with more than 50 % of oil phase “ internal phase”.

What the factors that affect the choice of emulsion type? The choice of emulsion depends on: Properties and uses of final products. (2) The other material required to be present. Oil-soluble drug is prepared in o/w emulsion due its solubility and its taste can be masked by adding flavoring agents.

W/O vs. O/W emulsions Bancroft's rule Emulsion type depends more on the nature of the emulsifying agent than on the relative proportions of oil or water present or the methodology of preparing emulsion. The phase in which an emulsifier is more soluble constitutes the continuous phase In O/W emulsions – emulsifying agents are more soluble in water than in oil (High HLB surfactants). In W/O emulsions – emulsifying agents are more soluble in oil than in water (Low HLB surfactants).

THE HYDROPHILIC - LIPOPHILIC BALANCE SYSTEM (HLB) Synthetic surfactants which are non-ionic in nature have hydrophilic and lipophilic portions which orient themselves at the oil-water interface. Usually one or the other, that is the hydrophilic or lipophilic portion, is predominant, and determines whether the emulsion formed is of the oil-in-water type or the water-in-oil type. These surfactants , as well as some naturally occurring ones, have been assigned an HLB number which describes its hydro- or lipophilicity.

The theory behind HLB is that emulsifiers showing greater solubility in water would be better for oil in water emulsifications Emulsifiers showing great solubility in oil would be better for water in oil emulsifications. The lower HLB valued emulsifiers are better in water in oil as they are more lipophilic The higher valued HLB emulsifiers are more hydrophilic

The surfactants which are more hydrophilic form o/w emulsion and have a higher HLB number. tend to form w/o emulsions.   The more lipophilic agents have numbers in the range of 3 to 6, and and tend to form w/o emulsions.  In addition to the assignation of HLB numbers to emulsifying agents, numbers are assigned to oil and oil-like substances It is desirable to choose an emulsifier which has an HLB value close to that of the oil phase.

Calculation of HLB For the surfactant CH3(CH2)17-(OCH2CH2)3OH First find the formula weight of the molecule = 403 FW of head group = 44X3 + 17 = 149 HLB = (FW of head group/FW of molecule) * 20 = 7.4 HLB = (149/403) * 20 = 7.4 For the surfactant CH3(CH2)17-(OCH2CH2)20OH FW of molecule = 1150 FW of head group = 44X20 + 17 = 897 HLB = (FW of head group/FW of molecule) * 20 HLB = (897/1150) * 20 = 15.6 You should observe the increase in HLB as the head group becomes more polar

Thermal Inversion Phenomena An emulsion is "inverted" when the dispersed phase becomes the continuous phase and vice versa. Under normal circumstances, the emulsifier molecule will stay oriented in the correct direction. That is to say, the water-loving end (polar) stays in the water while the oil-loving end (non-polar) stays in the oil. Each end of the emulsifier molecule may have minor solubility in the opposite phase. Usually, they stay but preferring to be with their own.

Phase Inversion Temperature Generally, solubility (the ability to leave its own phase and break out of the emulsion) increases as temperature increases. Once this inversion begins, the emulsion becomes unstable and breaks apart. The specific temperature at which this destabilization takes place is known as the “phase inversion temperature.” Low phase inversion temperatures can limit processing as an emulsion will not form. This is why we recommend processing at no more than 60 C

Bancroft's rule Emulsion type depends more on the nature of the emulsifying agent than on the relative proportions of oil or water present or the methodology of preparing emulsion. Based on the Bancroft’s rule, it is possible to change an emulsion from O/W type to W/O type by inducing changes in surfactant HLB. In other words... Phase Inversion May be Induced.

Stability of Emulsions Stability is the most important property of emulsions There are three types of emulsions stability which are physical, chemical and microbiological stability An emulsion is called physically stable if its dispersed state does not change, i.e. if its droplet size distribution remains constant regardless of time. Droplets must not sediment or aggregate and changes in droplet sizes i.e. the growth of large droplets at the Expense of small ones.

The physical stability of emulsions during and immediately after emulsification, which called short-term stability, presents specific problems, too. The short-term stability of an emulsion indicates whether the newly formed droplets of an emulsion are sufficiently protected against aggregation during or directly after emulsification. Therefore, it decides on success or failure of the emulsification process that because emulsification processes are expected to not only size-reduce, but also to immediately stabilise these smaller droplets.

Droplets successfully protected against coalescence remain small, resulting in the desired in-disperse emulsion. If coalescence cannot be successfully prevented, droplets will flow together and form larger droplets. This could completely reverse the size reduction and it may cause emulsions to break. The chemical stability The chemical stability of an emulsion reflects its resistance against chemical changes. Mostly oxidation of fats and oils is the critical reaction for chemical deterioration of emulsions. The addition of antioxidants and protection against external influences such as light or excessive heat

Lotions and Creams lotions and creams are o/w emulsions. the major different between a lotion and a cream is the consistency lotions -- usually with an oil content ranging from 10% to 25% and it tend to be lighter in feel. creams usually with an oil content above 25% and tend to be denser and greasier. although lotion usually has a thinner consistency than cream], it can be made very thick by using more oil (solid at room temperature) and less oil (liquid at room temperature) and by using [more] thickening agents (e.g. stearic acid, cetyl alcohol, etc.).

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