Locally ordered junctions govern diffusion in triglycerides: insights from molecular dynamics simulations

Triglycerides (TGs) exhibit diverse flow behaviours that are essential for applications ranging from food and pharmaceuticals to renewable fuels and advanced lubricants. Despite sharing nearly identical atomic compositions and similar bulk thermodynamic properties, different TGs display markedly different viscosities, and the microscopic origins of these distinct behaviours remain unclear. Herein, we performed all-atom molecular dynamics simulations to investigate three representative TGs with different chain lengths and degrees of unsaturation: trioctanoin (8 : 0), triolein (18 : 1), and trilinolenin (18 : 3). Our results qualitatively reproduced the experimental viscosity ordering, with 18 : 1 being the most viscous and 8 : 0 showing a slightly higher viscosity than 18 : 3. Neither the cohesive energy density, melting point correlation, nor molecular size could account for these differences. Likewise, single-molecule conformational statistics and mesoscale cluster morphologies revealed no decisive distinctions that explain the observed viscosity variations. Instead, structural analyses revealed that the local parallel alignment of C-chain segments produced junctions that formed extended network structures. These networks were abundant in 18 : 1, intermediate in 8 : 0, and absent in 18 : 3, directly correlating with the observed viscosities. Overall, fine-scale packing appears to govern the dynamics of TGs.