Rheological and Photorheological Effects of 6-Alkyl Coumarins in Aqueous Micellar Solutions

Abstract

Viscosities of aqueous micellar solutions of cetyltrimethylammonium bromide (CTAB) and Triton X-100 were measured in the presence and absence of coumarin derivatives, mainly 6-alkyl coumarins with alkyl substituents between methyl and cetyl. The coumarins generally increased the viscosity; the extent of the increase was specific: alkyl chains of medium length showed the largest effects. In situ photodimerization of the coumarins led to a further rise in the viscosity for short alkyl substituents but to a drop in the viscosity in CTAB for long alkyl substituents. Thermodynamic parameters of micelle formation, determined from surface tension measurements, correlate with rheological changes and indicate an increased hydration of the micelles in the cases exhibiting a high viscosity.

Organization of amphiphiles

“…The G 0 m values at different temperatures without OP-30 compare well with the literature values [27].…”

“…During the determination of the intersection point (CMC) weight has been given to obtain two lines above and below the break (CMC) with different slopes and better regression coefficients. This method was standardized by determining the CMCs of CTAB and SDS, which compares well with literature values [27].…”

Organization of amphiphiles. Part XI: Physico-chemical aspects of mixed micellization involving normal conventional surfactant and a non-ionic gemini surfactant

“…The increase in conductivity of the solutions on addition of BAM indicates the interaction of BAM with the conventional surfactants [31,33]. The CMC values in absence of BAM of both the pure surfactants measured from conductivity data are found to be in good agreement with the values available in the literature [31][32][33]. The decrease in CMC and the degree of dissociation of the mixture with the addition of the non-ionic gemini surfactant (Table 1) suggest a synergistic interaction between the ionic surfactants and BAM.…”

“…This intersection point (CMC) is determined by selecting two lines above and below the break (CMC) having comparable difference in slope and better regression coefficient. This method was standardized by determining the CMC's of CTAB and SDS, which compares well with the literature values [31][32][33].…”

Light-responsive Wormlike Micelles

“…The authors further developed systems with photo-switchable viscosity by introducing coumarin derivatives into the aqueous solutions of Triton X-100 and CTAB [10]. They found that coumarins generally increased the viscosity, but the extent of the increase was specific: alkyl chains of medium length showed the largest effect.…”