Self-Assembly and Thermodynamic Properties of Dodecyldimethylethylammonium Bromide in Ethylene Glycol or Ethylene Glycol Oligomers and Water Mixed Solutions

Abstract

The self-assembly behavior of dodecyldimethylethylammonium bromide (DEDAB) in mixed solvent media of ethylene glycol (EG)/water, polyethylene glycol 200 (PEG 200)/water, or polyethylene glycol 400 (PEG 400)/water at different temperatures was studied via conductivity and isothermal titration microcalorimetry (ITC) methods. The results showed that the three systems generated traditional or swollen surfactant micelles with the addition of EG or PEG oligomers. The critical micelle concentration (cmc) of DEDAB increased with the increasing cosolvent amount in mixed solvent, chain length, or temperature. The decrease in the dielectric constant of the solvent and “structure-breaking effect” of the cosolvent were not conducive to the micellization of the surfactant. Regarding thermodynamics, Gibbs energy of micellization (ΔG m o) changes more positively in mixed solvent than pure water. According to the values of ΔH m o and −TΔS m o, micelle formation of the three systems was driven entropically as well as enthalpically within the studied temperature scope and solvent composition. A comparison of chain length of the cosolvents was conducted, showing that the effect of temperature and cosolvent amount on mixed aqueous solution on cmc and thermodynamic parameters was crucial.

Micellar Solution Behavior of Cetylpyridinium Surfactants in 2-Propanol–Water Mixed Media at Different Temperatures

“…The decrease in ε of the bulk phase can also cause an increase in surface area per headgroup of the micelles. The diffusion of mixed media into the palisade layer of the micelles can hinder the interaction of counterions with the micelles and can increase the α values . Furthermore, the reduction in ε of the bulk medium is expected to decrease the aggregation number of micelles reducing the charge desnsity around the micellar surface and this can also increase α values .…”

“…The diffusion of mixed media into the palisade layer of the micelles can hinder the interaction of counterions with the micelles and can increase the α values. 49 Furthermore, the reduction in ε of the bulk medium is expected to decrease the aggregation number of micelles reducing the charge desnsity around the micellar surface and this can also increase α values. 50 At the same time, a reduction in the α values (as found in some PrOH−WR compositions of their mixed media) is possible because of improved interaction between the counterions and opposite charged micellar headgroups caused by the change in the bulk properties of mixed media with the inclusion of PrOH.…”