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Abstract  

We have attempted to calculate the surface tension of some solids using immersion calorimetry measurements along with the interfacial model of van Oss [1, 2, 3, 4].

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Abstract  

Calorimetric measurements of adsorption for the surfactant (benzyldimethyldodecylammonium bromide) and its polar head-group (benzyltrimethylammonium bromide) from aqueous solutions on two different silica surfaces (hydrophilic and hydrophobic one) allow a more detailed picture of the subsequent stages of the adsorption process to be drawn. It is possible to determine more precisely a boundary between the adsorption of individual molecules and the formation of surface aggregates. The local disruption of the structure of the interfacial water molecules by surfactant cations gives an endothermic contribution to the total enthalpy of displacement. This contribution depends on the length of alkyl chain as well as on the type and the origin of solid surface.

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Abstract  

Differential scanning calorimetry (DSC) and isothermal calorimetric batch technique were used to monitor the heat-induced structural changes and adsorption properties of human immunoglobulin G (IgG), in native and hydrophobized states. The transition temperature (T max) and enthalpy of heat-induced conformational changes ( cal H) of IgG in solution as well as the enthalpy change accompanying the adsorption of IgG onto hydrophilic silica ( ads H), were shown to depend on the degree of the protein hydrophobicity (number of covalently attached alkyl chains). The adsorption enthalpy for all forms of IgG at all surface concentrations was found to be endothermic, that is the process is entropy driven. Factors affecting the IgG adsorption onto silica are discussed.

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Abstract  

A new batch titration microcalorimeter has been used for estimation of thermodynamic properties in various investigated colloidal systems. As examples, we present enthalpic and kinetic data obtained from this calorimetric device for four different processes widely encountered in colloid science: (i)  The dilution/micellization process of cationic gemini surfactants in aqueous solution. (ii)  The hydration process of non ionic surfactants in organic solution, i.e. the mechanism of micellar solubilization of water in the aggregates. (iii)  The complexation of calcium ions by polyacrylates sodium salts (PaNa). (iv)  The adsorption phenomenon of PaNa molecules on the calcium carbonate surface.

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Journal of Thermal Analysis and Calorimetry
Authors: J. Douillard, H. Malandrini, T. Zoungrana, F. Clauss, and S. Partyka

Abstract  

It is possible to estimate surface tension of high-energy solids combining the immersion microcalorimetry thermodynamics and Van Oss' model. In this study we have applied this method on talc and talc-chlorite samples in order to obtain thermodynamic values which permit to understand surface properties useful in the industrial applications of these solids. Some talcite samples are preferentially used in specific industrial applications because they are less hydrophobic or more lamellar. This method seems to be reliable to classify the solids and predict some properties.

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Abstract  

The critical micelle concentrations and the enthalpies of micellization of alkyltrimethylammonium bromides having dodecyl, tetradecyl and hexadecyl hydrocarbon chains have been studied using surface tension and calorimetry measurements as a function of temperature. As expected, the change of critical micelle concentrations is very small with an increase of temperature of 10 deg whereas we observe a drastic change of the enthalpies of micellization. As it has been found by applying the Van't Hoff law to thecmc values at different temperatures, the calorimetric measurements show that the enthalpy of micellization, exothermic above a minimal temperature, becomes endothermic below this temperature.

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Application of the calorimetry to studies of colloidal phenomena

Enthalpies of micellization and enthalpies of adsorption of zwitterionic surfactants onto silica gel

Journal of Thermal Analysis and Calorimetry
Authors: J. Zajac, M. Chorro, C. Chorro, and S. Partyka

Abstract  

The importance of calorimetric methods in studies of colloidal phenomena is illustrated by the analysis of the experimental enthalpies of dilution and adsorption for aqueous solutions of three zwitterionic surfactants: 1–12 betaine, 3–12 betaine, and 3–12 sulfobetaine. The batch microcalorimeter ‘Montcal 3’, used to obtain these data, is described. The molar enthalpies of micellization and the differential molar enthalpies of adsorption onto silica gel are shown to be functions of the headgroup hydrophilicity, fixed by the type of negatively charged center and the number of methylene groups separating the charged sites.

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