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Thermodynamics of Self-Assembling of Hydrophobically Modified Cationic Polysaccharides and Their Mixtures with Oppositely Charged Surfactants in Aqueous Solution

Guangyue Bai,^† Marieta Nichifor,^‡^§ António Lopes,^‡ and Margarida Bastos*^†

CIQ (UP), Department of Chemistry, Faculty of Sciences, University of Porto, R. Campo Alegre, 687, P-4169-007 Porto, Portugal, Instituto de Tecnologia Qumica e Biolgica (ITQB/UNL), P-2781-901 Oeiras, Portugal, and Petru Poni Institute of Macromolecular Chemistry, Iasi, Romania

J. Phys. Chem. B, 2005, 109 (46), pp 21681–21689

DOI: 10.1021/jp054154i

Publication Date (Web): October 21, 2005

†

University of Porto.

‡

Instituto de Tecnologica Química e Biologica.

Institute of Macromolecular Chemistry.

To whom correspondence should be addressed. Fax: +351-22-6082959. E-mail: mbastos@fc.up.pt.

Abstract

Microcalorimetric techniques, combined with turbidity measurements, were used to study the thermodynamics of self-assembling of hydrophobically modified cationic polysaccharides and their mixtures with oppositely charged surfactants in aqueous solution. The studied polyelectrolytes were a series of polymers based on dextran having pendant N-(2-hydroxypropyl)-N,N-dimethyl-N-alkylammonium chloride groups randomly distributed along the polymer backbone. The parameters for their micellization process are evaluated from the results of the observed dilution enthalpy curves and compared with those of the related cationic surfactants (DTAC and CTAC). The microcalorimetric results for the mixed systems (polyelectrolytes with oppositely charged surfactants) are used along with turbidity measurements to characterize systematically the thermodynamics of their interaction. The phase behavior is described and the interaction enthalpies are derived from the differences between the observed enthalpy curves with and without polyelectrolyte. Therefore, we discuss in detail the effect of changing the alkyl chain length of polyelectrolyte pendant groups, the molecular weight of the dextran backbone, and the temperature of the measurements on the interactions between polyelectrolyte and surfactant.

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