Spectral characterization and colloidal properties of 1-hexadecylpyridinium chloride in aqueous binary mixtures of different glycols

Abstract

The influence of various water–glycol mixed solvents on the self-assembly of 1-hexadecylpyridinium chloride (CPyCl) was investigated using electrical conductivity and spectroscopic measurements. Temperature studies were performed in aqueous mixtures of ethylene, diethylene, triethylene and tetraethylene glycols (abbreviated as EG, DEG, TEG and TeEG, respectively). The correlation among critical micellization concentration (cmc) and degree of ionization ( β) was discussed in term of thermodynamic parameters or the changes in the Gibbs free energy, enthalpy and entropy upon micelle formation ( Δ G m 0 , Δ H m 0 and Δ S m 0 ). The differences in the Gibbs energies of micellization of CPyCl between water and binary solvents were determined to evaluate the influence of the cosolvent. This study allowed us to conclude that the ability of glycols to act, as a structure breaker and its interaction with the surfactant hydrophilic groups are the controlling factors of the micellization process. The effect of cosolvents on the size of the aggregates was analyzed by means of density measurements. Micellar micropolarity and solute solvent parameters were examined spectrophotometrically using methyl orange (MO) as a probe. The increase in micellar microviscosity was revealed from fluorescence measurements. The mechanism of docking of surfactant and the probe molecules in the system were obtained by using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy.