Contribution of microcalorimetry to the study of adsorption mechanisms of ionic and non-ionic molecules at the solid-water interface

Calorimetric Evidence of the Formation of Half-Cylindrical Aggregates of a Cationic Surfactant at the Graphite/Water Interface

“…The combination of adsorption isotherms with sorption microcalorimetric data has proved to be a powerful method for screening a variety of surfactant/adsorbent interactions. To date, most calorimetric studies have been directed toward the adsorption from aqueous solutions of nonionic − and ionic ,,− surfactants on hydrophilic surfaces , e.g., silica, alumina, clays, etc. It has been established that weakly adsorbed surfactant molecules at low concentrations (low-affinity region of the adsorption isotherm) will induce surface aggregation at higher concentrations as the critical micelle concentration (cmc) in the bulk solution is approached (high-affinity region).…”

“…Less attention has been paid to the microcalorimetric investigations of the adsorption from aqueous solutions of nonionic ,,− and ionic ,,− surfactants on hydrophobic surfaces , e.g., activated carbon, carbon black, and graphitized carbon black (gcb). The mechanism of the adsorption and the structure of the adsorption layer are also less well-understood.…”

Adsorption and Aggregation of C8E4 and C8G1 Nonionic Surfactants on Hydrophilic Silica Studied by Calorimetry

“…Among the various experimental techniques, calorimetry is a most sensitive tool for elucidating the thermodynamic behavior of surfactants both in the bulk solution [45][46][47][48][49] and at the solid/liquid interface. [27][28][29][30][31][32][33][34][35][36][37][38] In particular, the cmc and the aggregation number, 45,46 the heat of micelle formation, [45][46][47][48] and the heat of solution of monomeric surfactants in water 45,47,49 can be determined in the bulk liquid phase. On the other hand, sorption calorimetry has been used to measure the enthalpy balance of adsorption of C m PE n and C m E n nonionic surfactants on hydrophilic silica at ambient temperature.…”

“…On the other hand, sorption calorimetry has been used to measure the enthalpy balance of adsorption of C m PE n and C m E n nonionic surfactants on hydrophilic silica at ambient temperature. [27][28][29][30][31][32][33][34][35][36][37][38] The main feature of the (integral) enthalpy isotherms is, that while the adsorption is an exothermic process well below the cmc, it turns toward the endothermic direction at the csac and approaches a plateau beyond, but close to the cmc. The calorimetric evidence of the formation of surface aggregates is that, in the cooperative adsorption region, the measured differential molar heats of sorption are remarkably similar in magnitude to the corresponding molar enthalpies of micelle formation in the bulk solution and are less dependent on the nature of the silica.…”

Calorimetric study of adsorption of non-ionic surfactants on silica gels: Estimating the role of lateral interactions between surface aggregates

“…More recently the measurements of adsorption isotherms have been supplemented by a variety of experimental techniques like contact angle measurements, [27][28][29][30] X-ray diffraction, 29 neutron scattering and/or reflection techniques, 31-35 1 H or 13 C NMR spectroscopy, 34,36 fluorescence decay spectroscopy, [1][2][3]37,38 ellipsometry, [39][40][41] stability measurements, 32,33,42 and adsorption calorimetry. [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] Among various experimental techniques, calorimetry is believed to be the most sensitive tool for elucidating the thermodynamic features of surfactant bulk solutions, and their adsorption at the solid/liquid interface. From a theoretical viewpoint this is a direct measurement of the change in enthalpy.…”