Understanding Surfactants and New Methods of Dispersing
Chemists and process engineers far and wide find that their job is commonly a never-ending rush to what could be made better. Ideas on how to control processing costs or improve product quality come by through careful research, sudden creativity or sometimes, as the humble will admit, sheer luck. But implementing any solution ultimately requires multiple tools and approaches.
The key phrase is continuing progress and us in the mixing business aim to contribute to the evolution of processing techniques. At least for those involved in the manufacture of emulsions or for enthusiasts of the subject matter, this article aims to inspire a fresh understanding of surfactants and how they can be processed optimally.
A Tension Grabber or Two
Surface-active agents, surfactants for short, are compounds that are amphiphilic in nature – part hydrophilic (has affinity for water or aqueous phases), part lipophilic (has affinity for oily or organic phases). The combination of these opposing affinities in the same molecule dictates the surfactant's ability to reduce surface and interfacial tensions.
When present at high concentrations (above what is known as critical micelle concentration or CMC), surfactant molecules will assemble in the bulk solution and form aggregates known as micelles. Because of this characteristic behavior of surfactants to orient at surfaces and to form micelles, they are able to perform certain basic functions.
Surfactants act as foaming agents, emulsifiers and dispersants, suspending gases, immiscible liquids, or solids, respectively, in water or some other liquid. Solubilisation, a function closely related to emulsification, refers to a condition where suspended droplets and surfactant micelles are of the same size. Finally, the function of detergency is a complex combination of all the previous functions. Surfactants suspend, solubilise, dissolve and separate soil from the surface being cleaned.
These functions are basically accomplished by a surfactant as it absorbs at the surfaces of the suspended material and forms a protective layer around each particle. This ultimately decreases the overall free energy of the system and increases stability of the solution by discouraging separation of the phases. In addition to surfactant effects, the stability of suspensions is related to particle size and density of the suspended material.
While all surfactants rely on their dual nature to deliver their functionality, the kind and level of surfactant vary widely for different applications. Chemically synthesized surfactants are commonly used in the petroleum, food and pharmaceutical industries. For medical applications, biosurfactants (produced by microorganisms) are useful as antimicrobial agents and immunomodulatory molecules. They are also common ingredients in agrochemicals, food, cosmetics, pharmaceuticals and personal products.