Rheology of thermo-gelling capillary suspensions

Rheological measurements were performed to examine the behavior of thermally responsive capillary suspensions. These capillary suspensions were prepared by dispersing laponite nanoparticles in a continuous oil phase and an immiscible secondary fluid consisting of an aqueous solution of a thermogelling polymer, Pluronic F127 (PF127). The addition of PF127 (which undergoes sol-gel transition at elevated temperatures) into the secondary phase resulted in a capillary-networked suspension whose rheology can be tailored by increasing the temperature above the gelling temperature of PF127. We investigated the yielding behavior of this system using dynamic oscillatory measurements at different temperatures. These suspensions yield via a two-step process which was observed as two distinct plateaus for storage modulus in a typical plot of storage modulus versus oscillation strain. This yielding behavior is attributed to the rupturing of the bicontinuous network structure at lower strains which is followed by the breakup of particle aggregates at larger strains.