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 (delta) begin to change and resonance peaks begins to broaden with the increase in concentration significantly below their critical micelle concentrations (cmc's). 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 cmc's, 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 cmc's, 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.

Conformation of Triton X-100 (TX-100) in the bulk and in aqueous solutions at concentrations higher and lower than the critical micellar concentration (cmc) was studied by NMR relaxation, two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY), and molecular simulation by HYPERCHEM. Results show that motion of TX-100 in dilute solution (0.5 cmc) is in the extreme narrowing condition. Molecules are in the single molecular state with an extended polyoxyethylene chain. In forming micelles, these hydrophilic polyoxyethylene chains, staying in the exterior of the micellar core, coil, bend, and align along the surface of the TX-100 micellar core, forming a layer thick in dimension and loose in structure around the micellar core with a certain number of water molecules included. This hydrophilic layer is in contact with the solvent, water, keeping the micellar solution stable. The micelle is spherical at 10 cmc. Motions of all of the protons of TX-100 in the bulk, even of those on the polyoxyethylene chain, are more restricted than motions of those in the micellar core. Exponential decay of the proton spin-spin relaxation of TX-100 in the bulk shows the absence of oriented self-aggregation. Very short internuclear distances of the protons between hydrophilic and hydrophobic parts of TX-100 bulk measured from the 2D NOESY spectrum show that the molecules are arranged randomly, closely, and uniformly, which is the origin for the high viscosity of TX-100 bulk. Results are discussed in terms of inter-and intramolecular interactions.