Characteristics of aggregation in aqueous solutions of dialkylpyrrolidinium bromides

The aggregation properties of three dialkylpyrrolidinium bromide ionic liquids have been studied using different experimental techniques, including isothermal titration calorimetry. On the one hand, this allowed the correlation between the thermodynamics of aggregation and the underlying structural...

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Bibliographic Details
Published in:Journal of colloid and interface science 2011-08, Vol.360 (2), p.606-616
Main Authors: Tariq, M., Podgoršek, A., Ferguson, J.L., Lopes, A., Costa Gomes, M.F., Pádua, A.A.H., Rebelo, L.P.N., Canongia Lopes, J.N.
Format: Article
Language:English
Subjects:
Agglomeration
Aqueous solutions
Binding
Bromides
cationic surfactants
Chemical Sciences
Chemistry
Colloidal state and disperse state
Critical micelle concentration
crystallization
differential scanning calorimetry
diffusivity
Dispersions
enthalpy
Enthalpy of micellization
Exact sciences and technology
fluorescence
General and physical chemistry
glass transition
Ionic liquids
melting point
Micelles. Thin films
nuclear magnetic resonance spectroscopy
Operators
or physical chemistry
Self-aggregation
surface tension
Surfactants
temperature
Theoretical and
thermogravimetry
titration
Water
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Summary:The aggregation properties of three dialkylpyrrolidinium bromide ionic liquids have been studied using different experimental techniques, including isothermal titration calorimetry. On the one hand, this allowed the correlation between the thermodynamics of aggregation and the underlying structural motifs and on the other, the establishment of a bridge between the selfaggregation behaviors of conventional and ionic liquid-based surfactants. [Display omitted] ► Self-aggregation properties in aqueous solution of pyrrolidinium-based ionic liquids. ► Interfacial tension, fluorescence spectroscopy, NMR, diffusion coefficients of ionic liquids in water. ► Enthalpy of micellization determined by isothermal titration calorimetry. ► Relationship between surfactant structure and thermodynamics of aggregation revealed. Three pyrrolidinium-based ionic liquids—N-dodecyl-N-methylpyrrolidinium bromide, N-butyl-N-octylpyrrolidinium bromide, and N-butyl-N-dodecylpyrrolodinium bromide—were synthesized and characterized by their decomposition temperatures (Td) measured by thermogravimetric analysis, and by their melting point (Tm), glass transition (Tg) and crystallization temperatures (Tcryst) determined by differential scanning calorimetry. Their self-aggregation properties in aqueous solution were studied and their behavior is compared with that of analogous conventional cationic surfactants, namely tetra-alkylammonium bromide salts. The critical micellar concentration, cmcs were obtained by isothermal titration calorimetry (ITC); which were further validated by measurements of interfacial tension, fluorescence and NMR spectroscopy. Enthalpies of micellization were measured at three different temperatures using ITC. The Taylor dispersion method and DOSY NMR were used to determine diffusion coefficients of the ionic liquid surfactants in aqueous solution at 298.15K. Several correlations between structural features of the surfactant species, such as the number and size of their alkyl chains, and the thermodynamic quantities of micellization—expressed by experimental values of cmc, counter-ion binding fraction, ΔmicG∘, ΔmicH∘, and ΔmicS∘—are established. We could interpret the different contributions of the two alkyl side chains to the aggregation properties in terms of the balance of interactions in homogeneous and micellar phases, contributing to understanding the aggregation behavior of ionic liquids in water and the parallel between these systems and traditional ionic su
ISSN:0021-9797
1095-7103
DOI:10.1016/j.jcis.2011.04.083