Yield Properties of Wax Crystal Structures Formed in Lubricant Mineral Oils

Abstract

On being cooled to temperatures well below the onset temperature for wax crystallization, mineral oils undergo a transition from viscous to elastic-solid (G‘ ≫ G‘ ‘) behavior, referred to as gelation. Gelation is caused by the formation of a wax crystal network and is distinct from a glass transition. We investigate the yield behavior of gelled mineral oils, linear elastic and fracture yield limits, as a function of the amount of crystallized wax and the particle size distribution of the wax by studying yield behavior as a function of temperature. By cooling the mineral oils at different constant cooling rates, we altered the surface-area-average crystal length (ls) in the wax crystal network. The observed yield behavior is compared to that reported for gels formed from flocculated or aggregated colloidal particles; gelled mineral oils exhibit a weak-link type of scaling in contrast to the strong-link scaling exhibited by flocculated colloidal gels.