UC Davis

This work evaluates the ability of various lipid-based amphiphilic small molecules (ASMs) to modulate the mechanical and rheological properties of oleogels principally structured by ethyl cellulose (EC). Six ASMs varying in the chemical structure of their polar headgroups were used to produce EC-ASM oleogels. Stearic acid (StAc), monoacylglycerol (MAG), sodium stearoyl lactylate (SSL), and citric acid esters of monoglycerides (CITREM) all provided a dramatic enhancement in gel strength, while lactic acid (LACTEM) and acetic acid (ACETEM) esters produced only a marginal increase. Those additives which crystallized above 20 °C displayed pronounced changes in their network organization and crystal morphology in the presence of EC. Differences in the solid/liquid phase change behavior were also observed in select samples using differential scanning calorimetry. Both the small and large amplitude oscillatory shear responses were dependent on the ASM which was dependent on the chemistry of the headgroup, crystal network organization, and ability to plasticize the polymer network. The extent of thixotropic recovery was largely dependent on the polarity of functional groups in the ASMs, but was also influenced by the formation of a secondary crystal network. In general, ASMs which formed larger, system-spanning crystal networks (MAG, StAc) produced more brittle gels, while the highly hydrophilic, charged headgroup of SSL promoted a homogeneous distribution of small crystals, resulting in a tougher material. In the absence of a crystal network, stronger polar species in the ASM headgroup produced higher gel strength and increased elasticity. Thus, both ASM chemical structure and crystallization properties strongly contribute to the functionality of the resulting combined oleogelator systems.