Physicochemical Studies on the Interfacial and Micellization Behavior of CTAB in Aqueous Polyethylene Glycol Media |
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Authors: | Kausik Manna Amiya Kumar Panda |
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Affiliation: | (1) Department of Chemistry, University of North Bengal, Darjeeling, 734 013, West Bengal, India; |
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Abstract: | Interfacial and micellization behavior of cetyltrimethylammonium bromide (CTAB) have been studied in aqueous polyethylene
glycol (PEG) mixed solvent systems of varying concentrations and molar mass. Interfacial behavior of CTAB was investigated
by the equilibrium surface tension method. Conductance studies of surfactant solutions under different condition helped in
determining the critical micelle concentration (CMC) and degree of dissociation of CTAB micelles. In addition, the limiting
molar conductivity of surfactant and micellar species were evaluated from the differential plots. The CMC of CTAB was found
to increase with increasing PEG concentration as well as its molar mass, although, the process of interfacial adsorption and
micellization was found to be spontaneous, as evidenced by negative free energy change. The viscosity of CTAB micelles in
aqueous-PEG mixtures was found to increase with the increase in PEG concentration and molar mass. Dynamic light scattering
measurements revealed a size enhancement effect contributed by the PEG oligomers. An increase in the CMC of CTAB and the subsequent
presence of a higher number of ionic species in their dissociated form was further established by an overall increase in the
zeta potential value in the presence of PEG oligomers. It is proposed that the PEG could wrap around the micelles through
their conformational changes. Results also suggest that PEG oligomers could give solvophobic effect which enhances the CMC
of CTAB compared to that in pure water. |
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