Question

How micelles are obtained ? Give also mechanism

Answer 1

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Mechanism of Surfactant Micelle Formation

Xiaohong Cui†‡, Shizhen Mao†, Maili Liu†, Hanzhen Yuan† and Youru Du†

* Corresponding author. E-mail address: [email protected] (S.Z.M.); [email protected] (M.L.L.). Tel.:86-27-87197305. Fax: 86-27-87199291.

† Wuhan Institute of Physics and Mathematics.

‡ Graduate School.

State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China, Graduate School, Chinese Academy of Science, Beijing 100029, P. R. China

Langmuir

Vol. 24: , Issue. 19, : Pages. 10771-10775

Publication Date (Web): August 26, 2008

https://doi.org/10.1021/la801705y

The mechanism of micelle formation of surfactants sodium dodecyl sulfate (SDS), n-hexyldecyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100) in heavy water solutions was studied by 1H NMR (chemical shift and line shape) and NMR self-diffusion experiments.1H NMR and self-diffusion experiments of these three surfactants show that their chemical shifts (δ) begin to change and resonance peaks begins to broaden with the increase in concentration significantly below their critical micelle concentrations (cmcʼs). At the same time, self-diffusion coefficients (D) of the surfactant molecules decrease simultaneously as their concentrations increase. These indicate that when the concentrations are near and lower than their cmcʼs, there are oligomers (premicelles) formed in these three surfactant systems. Carefully examining the dependence of chemical shift and self-diffusion coefficient on concentration in the region just slightly above their cmcʼs, one finds that the pseudophase transition model is not applicable to the variation of physical properties (chemical shift and self-diffusion coefficient) with concentration of these systems. This indicates that premicelles still exist in this concentration region along with the formation of micelles. The curved dependence of chemical shift and self-diffusion coefficient on the increase in concentration suggests that the premicelles grow as the concentration increases until a definite value when the size of the premicelle reaches that of the micelle, i.e., the system is likely dominated by the monomers and micelles. Additionally, the approximate values of premicelle coming forth concentration (pmc) and cmc were obtained by again fitting chemical shifts to reciprocals of concentrations at a different perspective, and are in good accordant with experimental results and literature values and prove the former conclusion.

Answer 2

When molecular ions in soaps and detergents aggregate, they form Micelles.
It is because large number of molecular ions of soaps get aggregated and form colloidal solution. Soaps has hydrophobic tail which dissolves in hydrocarbon part and hydrophillic part dissolves in water.