Influence of Measuring Geometry on Rheomalaxis of Macrocrystalline Wax–Oil Gels: Alteration of Breakage Mechanism from Adhesive to Cohesive

Abstract

Rheological measurement of wax–oil gel breakage is highly susceptible to the phenomenon of adhesive breakage, hindering instrument-scale replication of cohesive breakage processes. Adhesive breakage measurements are notoriously irreproducible due to strongly nonaffine gel deformation. Efforts to ensure mechanical fixation give rise to spatially inhomogeneous deformation fields in the measuring geometry, particularly with respect to azimuthal and radial location. To elucidate the functional role of mechanically fixating geometries during gel breakage processes, three model solutions were prepared containing 5, 7.5, and 10 wt % macrocrystalline wax in dodecane. Rheograms were acquired in controlled deformation mode at imposed shear rates in the range of 0.1–1.0 s–1 using a vane or a cone and plate geometry. Yield stress values, nominally ascribed to primary peak height, were established based on 95% confidence intervals. Yielding trends confirm that adhesive breakage is particularly pronounced in high solid...