n-decyl-glucopyranoside and n-decyl-maltopyranoside Gibbs monolayers. Phase changes in the dilute liquid-expanded range
2004 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, no 24, 10534-10541 p.Article in journal (Refereed) Published
Surface tension isotherms were recorded for n-decyl-beta-(D)-glucopyranoside (Glu) and n-deCyl-beta-(D)-maltopyranoside (Mal) solutions at temperatures of 8,22, and 29degreesC. Comparison was made with isotherms of n-deCyl-beta-(D)-thiomaltopyranoside (S-Mal) at 22 degreesC. In addition to the transition from the gaseous to the liquid-expanded (LE) state, a second transition was observed in the early stages of the LE regime for Glu, Mal, and S-Mal at room temperature. The adsorption isotherm of Mal and Glu obtained at 22 degreesC shows the presence of an adsorption step at an average area/molecule of about 79 Angstrom(2) between, approximately, 0.02 and 0.1 mM (the critical micelle concentration (cmc) is 2 mM) and 0.015 and 0.03 mM (the cmc is 2 mM), respectively. Similarly, for S-Mal an adsorption plateau is observed at 70 Angstrom(2) between 0.01 and 0.03 mM (the cmc is 0.7 mM). From the temperature dependence of the surface tension, we have seen that there are considerable differences in the adsorption of Glu and Mal. For Mal, the adsorption plateau is also observed at 29 degreesC at around 79 Angstrom(2), whereas Glu exhibits no adsorption plateau at this temperature. At 8 degreesC, both Mal and Glu exhibit saturation behaviour in the dilute part of the liquid-expanded range, but at this temperature the average molecular areas are lower than at 22 degreesC: around 66 Angstrom(2) for Glu and 75 Angstrom(2) for Mal. Thus, the temperature sensitivity of Glu is considerably greater than for Mal in this range. The saturation regime coincides with a pronounced surface entropy minimum for Mal. The transition in the dilute liquid-expanded range supposedly occurs from a state with deformed surface micelles arranged in a hexagonal pattern, referred to as the granular range, to a true LE monolayer with a fluid hydrocarbon tail layer covering the entire surface.
Place, publisher, year, edition, pages
2004. Vol. 20, no 24, 10534-10541 p.
Free energy, Hydrocarbons, Isotherms, Micelles, Monolayers, Surface active agents, Surface tension, Thermodynamics
IdentifiersURN: urn:nbn:se:kth:diva-40288DOI: 10.1021/la0488497ISI: 000225207400025OAI: oai:DiVA.org:kth-40288DiVA: diva2:441457
QC 201109162011-09-162011-09-142011-09-16Bibliographically approved