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    Conductometric studies of hexadecyltrimethylammonium bromide in aqueous solutions of ethanol and ethylene glycol
    (Pleiades Publishing Inc, 2006) Akbas, H; Kartal, Ç
    The effect of cosolvent on micellization of hexadecyltrimethyl ammonium bromide (CTAB) in aqueous solutions was studied. The conductivity of a mixture (cosolvent + water) as function of CTAB concentration was measured at different temperatures. Ethylene glycol and ethanol were used as a cosolvent. The conductivity data were used to determine the critical micelle concentration (CMC) and the effective degree of counterion dissociation of micelle in the temperature range 303.2 to 313.2 K. In all the cases studied, a linear relatoinship between log([CMC](mix)/mol dm(-3)) and the mass fraction of cosolvent in solvent mixture has been observed. The free energy (Delta G(mic)(0)), enthalpy (Delta H-mic(0)), and entropy (Delta S-mic(0)) of micellization were determined using the temperature dependence of CMC. The dependence of these thermodynamic parameters on solvent composition was determined. The standard free energy of micellization was found to be negative in all cases and becomes less negative as the cosolvent content increases. The enthalpy and entropy of micellization are independent of temperature in pure water, while Delta H-mic(0) and Delta S-mic(0) decrease dramatically with temperature in mixed cosolvents. Furthermore, the entropic contribution is larger than the enthalpic one in pure water, while in the mixed solvents, the enthalpic contribution predominates.
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    Study on the interaction of anionic dye-nonionic surfactants in a mixture of anionic and nonionic surfactants by absorption spectroscopy
    (Elsevier Sci Ltd, 2005) Kartal, Ç; Akbas, H
    The interaction between an anionic dye C.I. Reactive Orange 16 (RO16) and different surfactants. i.e.. the anionic surfactant sodium dodecylsulfate (SDS) and nonionic surfactants polyoxyethylene ethers (CmPOEn; m = 12, 16 and 18, n = 4, 10 and 23) has been researched spectrophotometrically in a certain micellar concentration range. Light absorbances in the visible spectral range are measured as a function of mole fraction of surfactant at four different temperatures and at 24 h over the periodic time intervals. For this reason, a typical system occurred at 1.0 x 10(-2) mol/l for surfactants and at 1.0 x 10(-4) mol/l for dye concentrations. It is evident from the experimental measurements that while nonionic surfactants form a complex with the anionic dye RO16 in aqueous solution in studied concentration range, anionic surfactant does not. The formation of CmPOEn-RO16 complex in the SDS solutions of different mole fractions in its micellar concentration range has been determined and compared to those obtained in the dye-surfactant binary mixtures. Spectrophotometric measurements indicated that the value of absorbance of SDS-RO16 is greater than that of nonionic surfactant-RO16 in the binary systems. This state explains that the ionic and hydrophobic interactions between SDS-RO16 are less than that of nonionic surfactant-RO16 interactions. The addition of SDS to the mixture of CmPOEn-RO16 causes an increase in the value of absorbance. This increase is due to changed hydrophobic-hydrophilic balance of the studied mixtures. Furthermore, we observed that the alkyl chain length and the number of polyoxyethylene in nonionic surfactants do not have an enormous effect on the values of absorbance. (C) 2004 Elsevier Ltd. All rights reserved.