Interest in the fundamental properties of systems based on lipids (fat-like molecules that are insoluble in water) has increased owing to a growing number of applications in pharmacy, medicine
and food science. Investigation of the internal dynamics of lipid aggregates raises some important and yet-to-be-answered questions, including the effects of temperature on these motions.
Using Iris at ISIS and IN6 at ILL, we have explored a wide range of dynamics of lipid-based systems (energy-transfer range 10 μeV –5 meV). The quasielastic neutron scattering (QENS) data confirm
the existence of dynamical heterogeneities, whereby the terminal ends of the acyl chains experience faster motions than those of the head groups and neighbouring chain segments. Owing to the larger available free volume, the terminal CH2 and methyl groups can also undergo torsional structural changes. The addition of chitosan, a charged polysaccharide used along with lipids in drug-delivery applications, affects the localised hydrogen motions on the upper part of the molecule yet they do not seem to influence the structural changes.