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Cationic Micelles Modulated in the Presence of α,ω‐Alkanediols: A SANS, NMR and Conductometric Study
Author(s) -
Chavda Suresh,
Singh Kulbir,
Gerrard Marangoni D.,
Aswal Vinod K.,
Bahadur Pratap
Publication year - 2012
Publication title -
journal of surfactants and detergents
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.349
H-Index - 48
eISSN - 1558-9293
pISSN - 1097-3958
DOI - 10.1007/s11743-011-1307-y
Subject(s) - chemistry , micelle , counterion , critical micelle concentration , bromide , pulmonary surfactant , solubility , solvent , cationic polymerization , phase (matter) , small angle neutron scattering , inorganic chemistry , neutron scattering , aqueous solution , organic chemistry , scattering , ion , biochemistry , physics , optics
The solution behavior of a typical cationic surfactant, tetradecyltrimethylammonium bromide, in mixed solvent systems composed of water and varying concentrations of α,ω‐alkanediols; 1,2‐ethanediol (ED), 1,4‐butanediol (BD), 1,6‐hexanediol (HD) and 1,8‐octanediol (OD) was examined via electrical conductance measurements, 13 C‐NMR spectroscopy and small angle neutron scattering (SANS) measurements. The critical micelle concentration (CMC) values and degree of counterion dissociation (α) indicate that both ED and BD oppose micellization, whereas HD and OD enhance micelle formation. Changes in the 13 C‐NMR chemical shifts (∆δ values) reveal that the short chain diols reside almost exclusively in the bulk phase and hence, affect the formation of micelles by altering the solvent properties in the bulk of the solution, whereas HD and OD partition between the pseudomicellar phase and the bulk phase. SANS studies indicated that both the micellar size and aggregation number ( N agg ) decrease in the presence of all diols. ED and BD behave like cosolvents and increase the α and CMC values and decrease N agg . We note that the effect of HD and OD on the properties of the micelles is concentration dependent; at low concentrations, these diols interact with the micelles and behave as cosurfactants (as evidenced by the trends in the micellar properties), while at higher concentrations, they enhance the surfactant solubility and behave as a cosolvent.