Scattering Techniques As Structural Investigation Tools of Colloidal Aggregates in Organic Media

Abstract

Colloids, such as those found in oil industry [1], are complex systems exhibiting specific viscoelastic properties. Among these industrial materials, lubricating greases are of special interest as they provide a good illustration of the important contribution of the scattering techniques to the structural investigation of self-assembling systems. They can be composed of numerous components and additives to meet specific needs (e.g. extreme pressure, anti-corrosion). However, greases made up of saponified fatty acids in mineral oils can be modeled with extremely simple binary systems thus favoring the analysis of the structural and mechanical properties within the appropriate fundamental context. A number of commercial lubricating greases contain lithium 12-hydroxy stearate (abbreviated as LiS-OH). Corresponding model systems are LiS-OH in organic liquids such as decalin, dodecane, nitrobenzene, etc. The selfassociation reactions of the LiS-OH molecules under appropriate thermodynamic conditions (concentration, temperature) give rise to colloidal aggregates. If the LiS-OH concentration is increased, the aggregates overlap to form three-dimensional networks. This structure provides specific mechanical properties which are the basis of the well-known industrial applications. These materials display all mechanical and thermal properties of rigid physical gels which constitute the reference background [2]. The fatty acid derivative (12-hydroxy stearic acid, SA-OH) also gives organogels but which exhibit a lower thermal stability in various aromatic and alkanic solvents; and can be used to complete the investigation of the mechanisms which govern the growth of the heterogeneous materials [3].