Macroemulsion

Macroemulsions are homogenous transparent thermodynamically unstable systems with particle sizes ranging from 5-140 nm, which form spontaneously when mixed in the correct ratio. Macroemulsions scatter light effectively and therefore appear milky, because their droplets are greater than a wavelength of light. They are part of a larger family of emulsions along with microemulsions. As with all emulsions, one phase serves as the dispersing agent. It is often called the continuous or outer phase. The remaining phase(s) are disperse or inner phase(s), because the liquid droplets are finely distributed amongst the larger continuous phase droplets. This type of emulsion is thermodynamically unstable, but can be stabilized for a period of time with applications of kinetic energy. Surfactants (emulsifiers) are used to reduce the interfacial tension between the two layers, and induce macroemulsion stability for a useful amount of time.Note 1: Macro-emulsions comprise large droplets and thus are 'unstable' in the sense that the droplets sediment or float, depending on the densities of the dispersed phase and dispersion medium. Separation of the dispersed and continuous phases usually occurs within time periods from a few seconds to a few hours, depending upon the viscosity of the fluid medium and the size and density of the droplets. Macroemulsions are homogenous transparent thermodynamically unstable systems with particle sizes ranging from 5-140 nm, which form spontaneously when mixed in the correct ratio. Macroemulsions scatter light effectively and therefore appear milky, because their droplets are greater than a wavelength of light. They are part of a larger family of emulsions along with microemulsions. As with all emulsions, one phase serves as the dispersing agent. It is often called the continuous or outer phase. The remaining phase(s) are disperse or inner phase(s), because the liquid droplets are finely distributed amongst the larger continuous phase droplets. This type of emulsion is thermodynamically unstable, but can be stabilized for a period of time with applications of kinetic energy. Surfactants (emulsifiers) are used to reduce the interfacial tension between the two layers, and induce macroemulsion stability for a useful amount of time. Macroemulsions can be divided into two main categories based on if they are a single emulsion or a double or multiple emulsion group. Both categories will be described using a typical oil (O) and water (W) immiscible fluid pairing. Single emulsions can be sub divided into two different types. For each single emulsion a single surfactant stabilizing layer exists as a buffer in between the two layers. In (O/W) oil droplets are dispersed in water. On the other hand, (W/O) involves water droplets finely dispersed in oil. Double or multiple emulsion classification is similar to single emulsion classification, except the immiscible phases are separated by at least two surfactant thin films. In a (W/O/W) combination, an immiscible oil phase exists between two separate water phases. In contrast, in an (O/W/O) combination the immiscible water phase separates two different oil phases. Macroemulsions are formed in a variety of ways. Since they are not thermodynamically stable, they do not form spontaneously and require energy input, usually in the form of stirring or shaking of some kind to mechanically mix the otherwise immiscible Phases. The resulting size of the macroemulsions typically depend on how much energy was used to mix the phases, with higher-energy mixing methods resulting in smaller emulsion particles. The energy required for this can be approximated using the following equation: Δ G e m = 3 γ V   R f {displaystyle Delta G_{ m {em}}=3{gamma V over R_{ m {f}}}} Where Δ G e m {displaystyle Delta G_{ m {em}}} is the Energy Input, γ {displaystyle gamma } is the interfacial tension between the two phases, V {displaystyle V} is the total volume of the mixture, and R f {displaystyle R_{ m {f}}} is the average radius of the newly created emulsions This equation gives the energy requirement just to separate the particles. In practice the energy cost is much higher, as most of the mechanical energy is simply converted to heat rather than mixing the phases.