Where do the pyrene molecules reside within the surface active ionic liquid micelles in presence of sodium alginate?

Abstract

Pyrene fluorescence in aqueous solutions of two surface active ionic liquids, namely, 1-decyl-3-methylimidazolium chloride, and 1-hexadecyl-3-methylimidazolium chloride was investigated in presence of a biopolymer sodium alginate. The principal objective of this study was to explore the influence of the length of the hydrocarbon tails of these surface active ionic liquids on the possible location of the probe (pyrene) molecules in presence of the additive. While an abrupt decrease in the values of the ratio of the intensity of the first vibronic band to that of the third band of pyrene emission spectrum with concentration was observed for 1-hexadecyl-3-methylimidazolium chloride in presence of sodium alginate like the polymer-free case reported earlier, there was a peculiar reversal for 1-decyl-3-methylimidazolium chloride + sodium alginate. The former system manifested a usual sigmoidal profile, but in contrast, the later revealed an inverse sigmoidal dependence. The results indicated preferential incorporation of the pyrene probe into the hydrophobic microenvironment of the 1-hexadecyl-3-methylimidazolium chloride micelles. On the other hand, the solubilized pyrene molecules could have been accommodated in a layer within the 1-decyl-3-methylimidazolium chloride micelles closer to the micellar surface. Fluorescence measurements also helped ascertain the aggregation numbers of the micelles in presence of sodium alginate.

Keywords: Aggregation number; Micelle; Pyrene fluorescence; Sodium alginate; Surface active ionic liquid.