Effect of alkyl chain length on the clustering of molten triacylglycerols

• A reduction of N C with increase in temperature is observed. • The glycerol-glycerol attraction in the small molecules is larger than in the bigger molecules. • TAGs form clusters via intermolecular attractions between glycerol cores. • The average number of molecules per cluster increases with the alkyl chain length. • The solid-state structure of TAGs is affected by their molten state. The alkyl chain length of triacylglycerols affects the average number of molecules per cluster ( N C ) in the molten state. These numbers are estimated for the homologous series trilaurin (C12), trimyristin (C14), tripalmitin (C16), and tristearin (C18). N C values are estimated from experimental results of in-house and synchrotron x-ray scattering and small angle neutron scattering. The temperatures are between 473 K (200 °C) and 5 K below the melting point of each polymorph. Numerical simulations were performed as well for a subset of these conditions. As for tripalmitin, a reduction of N C with increase in temperature is observed in the other materials. For trilaurin (C12), N C is between 6 at 473 K and 7.5 at 313 K. For tristearin (C18) this number ranges from 8 at 473 K to 10 at 335 K. For trimyristin (C14) and tripalmitin (C16) the values of are in between. Thus, N C increases with alkyl chain length. This trend arises from the competition of the attractive forces between the glycerol cores and the alkyl chains against the mobility of the molecules due to their kinetic energy. Although the relative glycerol-glycerol attraction in the small molecules is larger than in the bigger molecules, the bigger molecules have less mobility. This reduction in mobility predominates in the determination of N C .