Microemulsion technology for surfactants


Courtesy of SAS Environmental Services Ltd.

Specialist cleaning applbatbns in industry are now facing increased levels of scrutiny, due to the effect that chemical product efficiency and design have on technbal performance and company economics. In add it bn, more stringent SHE legislation is driving the need for more specialised and more effective cleaning agents to be produced.

The Surfactant Technologies (STL) Group of the UK has developed a revolutionary set of chemical materials, using microemulsion technobgy that is based on optimised surfactant design. The work has been funded to date by the Royal Society of Edinburgh, Scottish Enterprise and the Scottish Executive, in conjunction with Napier University.

The term surfactant is a contraction of 'surface-active agent', a phrase coined in 1950. A surface-active substance reduces the surface tension of a liquid in which it is dissolved. This effect derives from the fact that surfactants are amphipathic in their molecular structure, i.e. their molecules are composed of two groups of opposite solubility tendencies, as shown in Figure 1.

When molecules of this structure are introduced to an oil-water interface they align themselves at that interface, with the hydrophilb group being solubilised into the aqueous phase and the hydrophobic group being solubilised into the organb phase. If the surfactant molecular structure is linear, as in the case of sodium dodecyl sulphate (SDS), this results in the formation of a planar monolayer of surfactant molecules at the interface. With more active shearing and mixing, these types of surfactants are able to form oil-in-water (O/W) and water-in-oil (W/O) dispersions by forming droplet structures called micelles of one phase dispersed within the other.

If the structure of the surfactant molecule is designed precisely so that it has a flexible cone or wedge shape and possesses the correct hydrophile-lipophile balance (HLB) and other such charaderistbs to match the relative oil and water substrates, as can be achieved with Aerosol-OT (AOTj, then the surfactant film may spontaneously adopt a natural radius of curvature of the interface, which has a direction and magnitude without any need for an energy input.

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