Phase Behavior and Micro-Structure of Fat–Oil Mixtures: Engineering the Shape of Fat Clusters

The mechanical properties of fat–oil mixtures are dictated by the morphology of the fat crystal network, which in turn is strongly affected by the processing conditions. In this work the effect of uniform (linear) cooling rates on the size and shape of tribehenin (fat) clusters in isopropyl myristate (oil) was studied. The state of the fat–oil mixtures was comprehensively analyzed by establishing pseudo-phase diagrams via visual observations, brightfield and polarization microscopy at various cooling rates and fat concentrations. The microstructure of the constituent fat clusters undergo a shape transition from bundles of needles at low cooling rates to spherical clusters at high cooling rates. The network structures formed with these different shaped fat clusters were examined using rheology. At a given cooling rate, the storage modulus (Gʹ) of fat–oil mixtures versus fat concentration followed a power law relationship. For a given fat concentration, the fat crystal networks comprising of bundles of needles showed higher Gʹ values as compared to fat networks made of spherical clusters. While the fractal dimension of networks cooled at different cooling rates varied over a small range of 2.78–2.86, considerable change in the pre-exponential factor (γ) was observed. The results show the critical importance of processing conditions on the shape and size of fat clusters and its impact on the rheological properties of the fat crystal network.