Micelle Characterization by DLS: Bringing Viscosity into the Equation

Investigating particle size in a micellar solution using the Litesizer 500 while measuring viscosity using a Lovis 2000 ME viscometer coupled to a DMA 5000 M density meter proves the significance of correct dynamic viscosity to obtain accurate particle size with DLS.

Micelles are spherical aggregates of surfactants with surface-active and amphiphilic properties. If the concentration of surfactant is below the critical micelle concentration (CMC), surfactant molecules are free to move in solution and position themselves on surfaces. If the surfactant concentration is high enough to reach the CMC, surfactants spontaneously start to form micelles in solution.

When surfactant concentration increases, the number of micelles increases as well. Micelle properties are also influenced by pH, temperature and the ionic strength of the solvent. Disodium cocoamphoacetate is a mild amphiphilic surfactant which is derived from coconut oil fatty acids of different chain lengths. It is frequently used in skin and hair conditioning products because it conditions as well as cleanses. Moreover, it increases the foaming capacity of cosmetic formulations when used as a co-surfactant. Unlike other surfactants like sodium lauryl sulfate, which is very widely used in cosmetics, disodium cocoamphoacetate has a relatively low detergent capacity and is thus mild to the skin and non-irritating.

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