Disperse Systems (emulsions )

a mixture of two immiscible (unmixable) liquids, typically consisting of one liquid dispersed in the form of small droplets within another liquid.

creams lotions milk mayonnaise toothpaste

Lotions, creams, ointments, vitamin drops

the dispersed phase(internal phase) the continuous phase(external phase) The dispersed phase, comprising small droplets, is dispersed within the continuous phase. In oil-in-water (O/W) emulsions, water is the continuous phase, and oil droplets are dispersed. In water-in-oil (W/O) emulsions, it is the opposite, with oil as the continuous phase and water droplets dispersed within it.

no, because the dispersed droplets would eventually seperate from the continuous phase to reform the intial immiscible state

a term used to describe the force acting at the interface between two immiscible phases, such as between two liquids or between a liquid and a gas. It is the tendency of the interface to minimize its area, and it arises due to the difference in cohesive forces between molecules in the two phases.

prevents the complete mixing of immiscible liquids. It creates a barrier that resists the penetration of one liquid into the other, maintaining the distinct separation of phases influences the formation of droplets when one immiscible liquid is dispersed into another. It determines the size and shape of the droplets, with higher tension leading to smaller, more spherical droplets.

via the addition of a surfactant or an emulsifying agent

To lower interfacial tension and stabilise emulsion

no all emulsifying agents are surfactants, but not all surfactants are emulsifying agents. Emulsifying agents are a subset of surfactants that are specifically chosen for their ability to stabilize emulsions

a broad category of compounds that have both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts in their molecular structure. This dual nature allows surfactants to reduce the surface tension between immiscible phases, such as oil and water. Surfactants can act as emulsifying agents when used to stabilize emulsions by preventing the coalescence of dispersed droplets.

the dispersion is unstable and the globules undergocoalescence to form two separate layers of water and oil

Be non-toxic. Must not interfere with the stability and efficacy of the API. Be compatible with other ingredients in the formulation. Be stable to microorganisms. Possess little or no odour, taste or colour. Maintain stability of the emulsion for intended shelf-life. Molecule has 2 parts: hydrophilic and hydrophobic

Forms a coherent film around the globules of the dispersed phaseand prevent the coalescence of the droplets.

enhances stability by preventing autoxidation of the oil and rancidity/and or destruction of any sensitive components like vitamins, present in the emulsion

The primary emulsion refers to the initial emulsion formed when two immiscible liquids are mixed. In the context of O/W emulsions, it is the initial mixture where water is the continuous phase and oil is dispersed. For W/O emulsions, it is the initial mixture where oil is the continuous phase and water is dispersed. The primary emulsion is formed by combining the two phases along with an emulsifying agent.

Secondary emulsions can be formed by taking the primary emulsion and further emulsifying it with additional ingredients This additional emulsification process can result in the creation of finer droplets within the primary emulsion. Secondary emulsions can have different properties, such as improved stability or altered texture, compared to the primary emulsion.

By forming secondary emulsions with specific characteristics, pharmaceutical scientists can design controlled release systems. This allows for the gradual release of drugs over time, providing sustained therapeutic effects

the external/continuous phase this is the bancroft rule

Water soluble drugs are more quickly released from o/w emulsions while Oil soluble drugs are more quickly released from w/o emulsions Preferred for internal use as bitter taste of oils can be masked while w/o preferred for external use

mainly large droplets 10 μm to 100 μm mainly small droplets 0.1 μm to 10 μm very small droplets 10 to 100 nm

the smaller the droplet size the higher the emulsion stability

Hydrophilic-Lipophilic Balance

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