How triacylglycerol thermal history impacts film removal by surfactant solution

The physical and mechanical properties of triacylglycerols (TAGs), or 'fats', depend on their composition and thermal history which, in turn, impact crystal structure and morphology. We examine whether thermal history can be mechanistically related to film removal by a surfactant solution.

Model TAG mixtures, comprising triolein:tripalmitin:tristearin 0.5:0.3:0.2, were subjected to a range of cooling profiles from the melt (0.5-80°C/min, Newtonian and annealed), and the resulting solid films characterised by microscopy, X-ray diffraction, infrared spectroscopy, and contact angle measurements. Film removal from a model glass substrate by an aqueous surfactant solution of sodium dodecylsulphate and dodecyldimethylamine oxide at room temperature fixed at 25°C was examined under quiescent flow conditions.

Quantitative relations are established between TAG cooling profile, crystal structure and morphology, surface energy γ_SFE, and removal (or 'cleaning'). In general, films cooled slowly from the melt yield heterogeneous morphologies with predominantly β₁^' phase, higher polar γ_SFE, and faster removal timescales. By contrast, rapid cooling results in homogeneous films, rich in β₂^' phase, low polar γ_SFE, and long removal times. Our results elucidate the non-trivial impact of TAG thermal history, connecting the multiscale semi-crystalline structure to surface energy, and eventually to film delamination by micellar solutions.