Neutron diffraction studies of liquid and crystalline trilaurin

Abstract

Neutron diffraction has been employed to investigate the structure of trilaurin in both liquid and crystalline states. The combination of long-wavelength (4.5 Å) neutrons and wide angular ranges of detection (∼6<2θ[^o]<∼100) per mitted a large range of momentum transfer to be acceessed (∼0.15<Q[Å⁻¹]<∼2) in a single scan of the detector. The chemical technique of selective deuteration of chosen parts of the triglyceride molecules was used to enhance specific aspects of the diffraction pattern and elucidate structures formed. The well established layer structure in the solid phases was confirmed in the diffraction patterns. It was also established that long-range ordering in the solid resulting from chain-chain registry disappeared when the solid melts. However, we found no evidence for long-range ordering in the form of persistence of a layer-layer spacing correlation in the liquid state. We postulate from the diffraction patterns a molecular arrangement resembling the arrangement found in the nematic phase of liquid crystals, where the layer structure is relaxed from that smectic-like arrangement for the crystalline phase. The data also reveal that this lack of order is not dependent on temperature in the liquid phase and persists into the super-cooled region below the normal β melting point.