In lithium soap thickened greases, soap molecules form a fibrous network. This fundamental study investigated the arrangement of lithium 12-hydroxystearic acid molecules at the earliest stage of thickening in mineral oil. Experimental data suggested that an initial structure or arrangement of thickener molecules formed when about 4% soap thickener was dispersed in base oil. Rheological measurements showed that at this concentration, the mixture first exhibited viscoelastic properties with its solid-like storage modulus at about the same value as its liquid-like viscous modulus. This concentration was defined as the critical micelle concentration (CMC). Infrared analysis spectra were consistent with results from computer models that showed that the lowest energy arrangement for two lithium 12-hydroxystearic acid (Li-12HSA) molecules was a structure where the tails were opposite the head groups, due to a repulsion between the tail groups, and with the head groups in a planar arrangement.
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