Colloidal Guest Particles in Cubic MO-Phases: Transitory States and Phase Distortion

The cubic phases of mono-olein (MO) are suggestive for applications such as hosting matrixes, as reactive surfaces for catalysis, and as storage and release devices for aqueous and non-aqueous cargos as e.g. drugs. If functionalized, they may constitute the basis of a new type of minute semi-open containers to be used on demand. Here we present results from a systematic X-ray scattering study on MO-water systems, conducted as a sequence of subsequent SAXS-WAXS data acquisitions at seven stationary temperatures in a heat-cool cycle (293K→338K→293K). The samples were prepared in glass capillaries such that water uptake and the subsequent formation process of the MO-mesophases could be directly monitored in the interfacial region between an aqueous phase and MO in its dry solid state. The formation of lipid mesophase was initiated above the melting temperature of pure MO (308K). The approach was as well applied to watch the uptake and extent of inoculation of two different types of hydrophilized Au-nanoparticles (NPs) during the formation of the lipid mesophases phase was. The model cargos were chosen upon their size (1.8nm and 5.0nm) relative to the aqueous channels and cavities of the expected cubic MO-phases. The equilibration into cubic phase at the previously reported lattice parameters is sterically hampered, and transitory hexagonal states were observed in all samples before any cubic symmetry was assumed. The impact of the NP cargos on the structural details and stability of the mesophases will be presented and discussed.