In situ methods for studying adsorbed phases at the solid/liquid interface: microcalorimetry and ellipsometry

Abstract

The applications of calorimetric and ellipsometric methods to the understanding of adsorption phenomena occurring at the solid-liquid interface are presented with examples in the field of surfactant adsorption. The various experimental approaches are presented and compared, i.e., immersion calorimetry, titration calorimetry and liquid flow calorimetry. It is shown how they can be used to follow, in situ, the building steps of the surfactant adsorbed layer. On the other hand, ellipsometry allows the adsorption isotherm, the adsorption kinetics as well as the thickness of the adsorbed layer to be determined on well-defined flat surfaces.

Microcalorimetry Study of the Adsorption of Asphaltenes and Asphaltene Model Compounds at the Liquid–Solid Surface

“…Adsorption of a solute from a solution (e.g. asphaltenes from crude oil) is a physical phenomenon that is normally accompanied by a heat effect 18 . Hence experimental methods developed around microcalorimetry that allow the determination of the adsorption enthalpy (∆ ) are suitable for studying the adsorption mechanisms involved in these processes 19,20 .…”

Natural minerals and divided solids: methodology for understanding surface phenomena related to industrial uses and environmental problems

“…Ces phénomènes, présents à la surface des minéraux, que les charges soient permanentes, c'est-à-dire dues à des substitutions isomorphiques dans le réseau (cas principalement de certaines argiles et des micas par exemple), ou variables, comme on l'a présenté ci-dessus, sont responsables de l'adsorption des espèces ioniques de signes contraires lorsque la liaison normale adsorbat-adsorbant est de nature entièrement électrostatique (le cas le plus fréquent) [8]. Au voisinage du point de charge nulle, les molécules organiques riches en radicaux -OH, susceptibles de former des liaisons hydrogène avec les groupes oxo ou hydroxo superficiels, s'adsorbent préférentiellement [13,18,19,23].…”

“…Les performances de trois méthodes d'étude in situ de l'adsorption des tensioactifs sont présentées. Il s'agit de la microcalorimétrie de titration ou d'écoulement, qui permet la mesure des enthalpies de déplacement, l'ellipsométrie [18] et la spectroscopie infrarouge à transformée de Fourier couplée à la réflexion externe, qui donnent accès, sur surface lisse, à des mesures en temps réel, c'est-à-dire à l'étude de la cinétique d'adsorption. La réflexion externe a permis récemment de venir à bout d'un problème extrêmement complexe, la compréhension des mécanismes de rétention des sels d'acides gras sur un minéral à solubilité non négligeable -la fluorine [35] -, ouvrant ainsi…”

“…The presence of electrical surface charges either due to substitutions in the crystalline network (case of charged clay minerals and micas for instance) or to hydroxyl groups resulting from water dissociation, as presented above, explains the adsorption of ionic species of opposite charge when the normal adsorbate-adsorbent bond is mainly electrostatic in nature [8]. Around the PCN, organic molecules with numerous OH radicals that can form hydrogen bonds with the oxo or hydroxo surface groups are preferentially adsorbed [13,18,19,23]. In that pH range, colloidal suspensions coagulate, whereas they are stable for pH values corresponding to high charges ( 15 mV).…”

“…Retention mechanisms can be approached by combining (i) a thorough analysis of adsorption isotherms obtained from either the rest methods or, for low specific surface area samples, inverse chromatography techniques and (ii) spectroscopic investigations allowing to study the organisation of adsorbed molecules. In recent years, three in situ analytical methods that will be presented in this monograph [18,35] have provided new information, increasing our understanding of surfactant adsorption at solid surfaces. (i) The measurement of displacement enthalpies accompanying surfactant adsorption can now be obtained using microcalorimetic methods (either titration calorimetry or flux calorimetry).…”