A titration microcalorimetric study of the effects of halide counterions on vesicle-forming aggregation in aqueous solution of branched-chain alkylpyridinium surfactants
| Autor: | Michael J. Blandamer, Jesse M. de Gooijer, Jan B. F. N. Engberts |
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| Přispěvatelé: | Faculty of Science and Engineering, Stratingh Institute of Chemistry, Synthetische Organische Chemie, Moleculaire Anorganische Chemie |
| Jazyk: | Dutch; Flemish |
| Rok vydání: | 2000 |
| Předmět: |
chemistry.chemical_classification
Isothermal microcalorimetry vesicles Standard molar entropy Chemistry Vesicle Inorganic chemistry Enthalpy alkylpyridinium surfactants aggregation Halide titration microcalorimetry MICELLIZATION Standard enthalpy of formation Surfaces Coatings and Films Electronic Optical and Magnetic Materials Gibbs free energy Biomaterials symbols.namesake Colloid and Surface Chemistry MICELLE FORMATION THERMODYNAMICS symbols Counterion |
| Zdroj: | Journal of Colloid and Interface Science, 224(1), 4-10. ACADEMIC PRESS INC ELSEVIER SCIENCE |
| ISSN: | 0021-9797 |
| DOI: | 10.1006/jcis.1999.6668 |
| Popis: | Titration microcalorimetry is used to study the influences of iodide, bromide, and chloride counterions on the aggregation of vesicle-forming 1-methyl-4-(2-pentylheptyl)pyridinium halide surfactants. Formation of vesicles by these surfactants was characterised using transmission electron microscopy. When the counterion is changed at 303 K through the series iodide, bromide, to chloride, the critical vesicular concentration (cvc) increases and the enthalpy of vesicle formation changes from exo- to endothermic. With increase in temperature to 333 K, vesicle formation becomes strongly exothermic. Increasing the temperature leads to a decrease in enthalpy and entropy of vesicle formation for all three surfactants. However the standard Gibbs energy for vesicle formation is, perhaps surprisingly, largely unaffected by an increase in temperature, as a consequence of a compensating change in both standard entropy and standard enthalpy of vesicle formation. Interestingly, standard isobaric heat capacities of vesicle formation are negative, large in magnitude but not strikingly dependent on the counterion. We conclude that the driving force for vesicle formation can be understood in terms of overlap of the thermally labile hydrophobic hydration shells of the alkyl chains. Copyright 2000 Academic Press. |
| Databáze: | OpenAIRE |
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