Kulim Kht Critical micelle concentration (CMC)

Introduction
Critical micelle concentration (CMC) is defined as the
concentration of surfactants in which micelles are spontaneously
formed. Below the CMC point surfactant molecules tend
to accumulate at the interface, reducing surface tension. At
CMC, the surface tension of the solution does not change but
remains constant, as the gas-liquid interface is already saturated
with the surfactant molecules. Above the CMC point most of
the surfactant molecules are inside the bulk, aggregating into
micelles. When this occurs, the addition of surfactants just
increases the number of micelles and the surface tension becomes
independent of surfactant concentration.
There are several factors affecting the CMC point of a surfactant.
These include the amphiphile chain length, dissolved salts, the
structure of the head group, temperature, the structure of the
alkyl chain and polar additives. The effects of chain length, salts
and alcohol on the critical micelle concentration have been
widely studied [1]. The exact molar weight and impurities in
the surfactant also influence the CMC, and therefore a careful
purification of the surfactant is relevant. A common and much
studied surfactant found in many detergents is sodium dodecyl
sulfate (SDS). SDS is easily hydrolyzed to dodecanol, which can be
seen as a possible contaminant [2].
The critical micelle concentration is a useful measure also in
pharmacology. Silicon surfactants are important in pharmaceutical
and cosmetic industry due to their low price and technological
advantages [3]. Liposomes can be used to carry non-polar drug
molecules in blood where as polymeric nanoparticles are found
to be useful in selective delivery of cancer drugs [4]. Studies on
interfacial properties of these drug carrying compounds require
the full understanding of the molecule’s CMC.