P. Somasundaran et L. Huang, Adsorption/aggregation of surfactants and their mixtures at solid-liquid interfaces, ADV COLL IN, 88(1-2), 2000, pp. 179-208
Adsorption of surfactants and polymers at solid-liquid interfaces is used w
idely to modify interfacial properties in a variety of industrial processes
such as notation, ceramic processing, flocculation/dispersion, personal ca
re product formulation and enhanced oil recovery. The behavior of surfactan
ts and polymers at interfaces is determined by a number of forces, includin
g electrostatic attraction, covalent bonding, hydrogen bonding, hydrophobic
bonding, and solvation and desolvation of various species. The extent and
type of the forces involved varies depending on the adsorbate and the adsor
bent, and also the composition and other characteristics of the solvent and
dissolved components in it. The influence of such forces on the adsorption
behavior is reviewed here from a thermodynamics point of view. The experim
ental results from microcalorimetric and spectroscopic studies of adsorbed
layers of different surfactant and polymer systems at solid-liquid interfac
es are also presented. Calorimetric data from the adsorption of an anionic
surfactant, sodium octylbenzenesulfonate, and a non-ionic surfactant, dodec
yloxyheptaethoxyethylalcohol, and their mixtures on alumina, yielded import
ant thermodynamic information. It was found that the adsorption of anionic
surfactants alone on alumina was initially highly exothermic due to the ele
ctrostatic interaction with the substrate. Further adsorption leading to a
solloid (hemimicelle) formation is proposed to be mainly an entropy-driven
process. The entropy effect was found to be more pronounced for the adsorpt
ion of anionic-non-ionic surfactant mixtures than for the anionic surfactan
t alone. Fluorescence studies using a pyrene probe on an adsorbed surfactan
t and polymer layers, along with electron spin resonance (ESR) spectroscopy
, reveal the role of surface aggregation and the conformation of the adsorb
ed molecules in controlling the dispersion and wettability of the system. (
C) 2000 Elsevier Science B.V. All rights reserved.