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3 Polish Journal of Chemistry

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Thermodynamics of Liquid-Liquid Partition and Hydration of Aliphatic Ethers

Gniazdowska E., Narbuft J.

Polish Journal of Chemistry

2002

Vol. 76 / nr 1

111-116

Interaction between water and ethers in dilute aqueous solutions was investigated by water- heptane partition of twelve linear aliphatic ethers containing various number of carbon atoms (from 2 to 8), and one branched homologue. Standard free energy (Gibbs) and enthalpy of partition were calculated from partition constants and from their temperature dependence. The differences in the free energy and entropy result from different hydrophobic hydration of these amphiphilic solutes in the aqueous phase. The position of the oxygen atom in an ether molecule affects the hydrophilic-hydrophobic properties of the molecule. The methylene groups in the _ and _ positions in respect to the oxygen atom are distinctly less hydrophobic than those more distant, therefore, different are their hydrophobic contributions into standard thermodynamic functions of hydration. The commonly accepted group contribution models, which assume equal contributions from the same fragments irrespectively of their position (additivity principle), should be revised.

Sphere-Rod Transition of Micelles in Aqueous Nabr Solutions of Hexadecyltrimethylammonium Bromide

Zieliński R.

Polish Journal of Chemistry

1999

Vol. 73, nr 11

1819-1826

Effect of temperature on the formation of micelles in aqueous NaBr solutions of hexadecyltrimethylammonium bromide, C16TAB, has been studied within the range 25-50 C. the critical surfactant concentrations for sphere-rod transition of the micellar shape, were determined from the intersections of two straight line portions of the plots of the relationship between ultrasound velocity in the solutions and surfactant concentration.

Micelle formation in aqueous NaBr solutions of alkyltrimethylammonium bromides

Zieliński R.

Polish Journal of Chemistry

1998

Vol. 72, nr 1

127-136

Sound velocity in aqueous solutions of alkyltrimethylammonium bromides with alkyl chains of octyl, decyl, dodecyl and tetradecyl has been measured as a function of surfactant and NaBr concentration at 25 degree C. The critical micelle concentrations, CMC were determined from intersection of two straight line portions of the surfactant concentration dependence of sound velocity in the solutions. CMC decreases with the increase of ionic strength, following the Corrin-Harkins equation. The standard free energy of micelle formation was estimated from the CMC at different NaBr concentrations. It was presented as a sum of increments of the methylene and the polar head groups at each NaBr concentration. The methylene group contribution varies with NaBr concentration from -1.81 kJ/mol in water to -2.95 kJ/mol at salt concentrations higher than 0.5 m NaBr.