Temperature dependence of oxygen-and clumped isotope fractionation in carbonates: a study of travertines and tufas in the 6-95°C temperature range, Geochimica et Cosmochimica Acta (2015), doi: http://dx.doi.org/10.1016/j.gca. 2015.06.032 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. calibrations. For this reason there is a need to better understand the controls on isotope 25 fractionation especially on natural carbonates. In this study we analyzed oxygen, carbon and 26 clumped isotopes of a unique set of modern calcitic and aragonitic travertines, tufa and cave 27 deposits from natural springs and wells. Together these samples cover a temperature range 28 from 6 to 95°C. Travertine samples were collected close to the vents of the springs and from 29 pools, and tufa samples were collected from karstic creeks and a cave. The majority of our 30 vent and pool travertines and tufa samples show a carbonate-water oxygen isotope 31 fractionation comparable to the one of Tremaine et al. (2011)
The aggregation properties of three dicationic quaternary ammonium gemini surfactants with the same structure, except the spacer group, diethyl ether, six methylene, and p-xylyl, have been studied using electrical conductivity and fluorescence. The critical micelle concentration (cmc) and the micelle aggregation number (N) were determined, and the micropolarity and the microviscosity of the micelle were characterized. The micelle ionization degree (alpha) was obtained by a combination of the electrical conductivity data and the micelle aggregation number. Furthermore, the Gibbs free energy of micellization (deltaGmic) was studied. These results have shown that the nature of the spacer has an important effect on the aggregation properties of gemini surfactants in an aqueous solution. A hydrophilic, flexible spacer prompts micelle formation, which leads to a smaller cmc, smaller alpha, larger N, and more negative deltaGmic. Meanwhile, the microviscosity study indicates that the gemini surfactant with a hydrophilic, flexible spacer forms a more closely packed micelle structure than the one with a hydrophobic, rigid spacer.
Microcalorimetric measurements have been made on the series of gemini surfactants [CMH2M+1(CH3)2N(CH2)SN(CH3)2CMH2M+1] Br2, designated CMCSCMBr2, where M and S indicate the numbers of carbons in the
side chains and spacer respectively, for M = 12 and S = 3, 4, 6, 8, 10, 12. For comparison, parallel
measurements have been made on the series of double-chain, singly charged surfactants dodecyldimethylalkylammonium bromides, designated as C12CNBr with N = 1, 2, 4, 6, 8, 10, 12, where N is the number of
carbons in the secondary alkyl chain. The choice of this second series was to compare each CMCSCMBr2 with
its nearest equivalent monomer C12CS/2Br. The values of the critical micelle concentrations (cmc) were found
to be in good agreement with other measurements, showing a maximum at S = 4−6 for the geminis and a
nonlinear variation with chain length for the C12CNBr series. For both series of surfactants, the enthalpies of
micellization, ΔH
mic, are all exothermic and show a marked minimum in magnitude at S = 4−6 or N = 4−6.
The variation of ΔH
mic and ΔS
mic across both series shows that the balance between enthalpic and entropic
contributions to the process of micellization changes substantially with S or N.
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