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Comparatively Speaking: Amphilic vs. Non-amphilic Compounds
By: Anthony J. O'Lenick, Jr., Siltech LLC
Posted: March 24, 2009
The term amphilic refers to a compound that possesses at least two groups that, if present in pure a form rather than in a compound, are insoluble in one another. The groups that are most commonly encountered in amphilic compounds are oil and water. When a molecule contains groups that make it an amphile, the resulting product is surface active.
NaCl is an example of a material that is not amphilic. Consider a fully dissolved 1% solution of sodium chloride in water. This simple system has a sodium ion (Na+), a chloride ion (Cl-) and water (aqua) equally distributed over the entire mass of the system. The solution is clear and homogeneous.
Now consider a 1% solution of a surfactant. Surfactant, or surface-active agent, has a water-soluble head and a water-insoluble tail. Similar to NaCl, the well-known surfactant sodium lauryl sulfate (CAS 151-21-3) has two opposite ions but it is different in water. The presence of a large fatty portion makes the product surface active.
The ability for surface-active materials to provide desirable properties by lowering surface tension is an important reason to use surfactants. The SLS discussed above is added to water, a solvent that not only has a high surface tension, but also one in which the surfactant is soluble. SLS provides wetting, foam and detergency to the water by virtue of lowering its surface tension.
There are many such examples including nonstandard types. One example of a nonstandard surfactant system is alkyl silicone, which is used lower the surface tension of triglycerides and other oils in which they are soluble but that act like amphilic materials. It is perfectly legitimate to ask what the critical micelle concentration of cetyl dimethicone in olive oil is.