Gelation in Oleogels: A Rheological Framework for Soft Material Formulation

Oleogels formed using natural waxes undergo a sol-gel transition as the temperature decreases. Such a transition is due to the formation of a hierarchical three-dimensional crystalline network formed by the wax crystals. The properties at the interfaces of these crystals play a crucial role in shaping the overall viscoelastic response of bulk materials. Although this transition governs their processing and functional performance, it has not been examined using critical gelation theory. In this work, we investigate the sol-gel transition in beeswax-corn oil oleogels by performing a detailed linear viscoelastic analysis. When subjected to an oscillatory shear flow field while decreasing temperature, the dynamic moduli exhibit an identical power-law dependence on frequency at a certain temperature, confirming the existence of a critical gel state. We also obtain various critical scaling relations with respect to different linear viscoelastic properties in the pre-gel and post-gel states. Remarkably, the corresponding scaling exponents satisfy the hyperscaling relations, validating the critical gelation framework. We also quantify the effects of wax concentration, which cause an increase in the fractal dimension as well as the gel strength. We believe that this study provides the first comprehensive validation of the critical gelation theory for wax-based oleogels. This work also establishes a unified linear viscoelastic description of their sol-gel transition, offering a predictive framework for formulation and processing near the gel point. Finally, we create a logical design framework for manipulating the mechanical stiffness and thermal durability of oleogels for various applications, such as shape-retaining cosmetics and spreadable food products. This is achieved by correlating the scaling behavior with the composition as well as the thermal history of the oleogels.