A New Approach for the Characterization of Reverse Micellar Systems by Dynamic Light Scattering

Abstract

This paper reports the use of dynamic light scattering (DLS) to study reverse micelles formed by the water/Igepal CO-520/cyclohexane system over a large range of global compositions. A novel approach for data analysis is presented, based on the realization that micelles of a given size must be in equilibrium with free surfactant of a fixed concentration. Compilation of the DLS data into sets of fixed micelle size but differing global compositions therefore allows for the determination of parameters such as free surfactant concentration, micellar molar composition, surfactant interfacial area, and aggregation numbers. Importantly, this method gives access to the variation of each of these parameters with micelle size, as is essential for the characterization of reverse micelles formed by nonionic surfactants. This approach constitutes a significant complement to other available characterization methods. The analysis also provides insight into the primary factors controlling the equilibrium distribution of surfactant within the system and the relative stability of the micelles.

Structure and dynamics of water in nonionic reverse micelles: A combined time-resolved infrared and small angle x-ray scattering study

“…Mostly, they show that the PEO chain penetrates the water volume and dangles freely in the water body. 31,52 We can test this hypothesis with our measurements: for reverse micelles with w • = 5, there are twice as many oxygen lone pairs available from the Igepal molecules as there are water molecules (5 ether groups per Igepal × 2 number of lone pairs per ether/5 water molecules per Igepal). This would imply that if the hydrophilic chains would completely penetrate the reverse micellar interior, all water molecules would be perturbed.…”

“…The conformation of the hydrophilic polyethylene oxide (PEO) chain in nonionic reverse micelles is still a matter of controversy. 23,31,51,52 Numerous papers depict the structure of a nonionic reverse micelle. Mostly, they show that the PEO chain penetrates the water volume and dangles freely in the water body.…”

Converting oils high in phospholipids to biodiesel using immobilized Aspergillus oryzae whole-cell biocatalysts expressing Fusarium heterosporum lipase

“…In the formation of reverse micelles, there always exists an amount of free surfactant, which is far from negligible [31]. With a fixed amount of water and an increase in phospholipids, more free surfactant remained in the system, and this free amphiphilic surfactant facilitated the mixing of the non-polar oil and polar methanol and slightly promoted methanolysis, as shown in Fig.…”

The mixing behaviour of anionic and nonionic surfactant blends in aqueous environment correlates in fatty acid ester medium

“…We calculate the aggregation number (N agg ) of RM systems at a fixed w 0 = 10 by using the following expression [78] and details are given in Supplementary material (Section 1);…”

“…The model assumes RMs to be compact spheres and neglects the presence of solvent molecules between the surfactant hydrophobic tails [78]. A representative plot of N agg as a function of X Tween-85 for these systems is depicted in Fig.…”