Effect of temperature and humidity on coarsening behavior of Au nanoparticles embedded in liquid crystalline lipid membrane.

Coarsening behavior of the Au nanoparticles produced by thermal evaporation of Au onto a liquid crystalline lipid (1,2-dioleoyl-3-trimethylammonium-propane, DOTAP) membrane was investigated by subjecting the nanoparticle-embedded DOTAP membrane to two different annealing conditions (at 100 °C under no humidity and at 20 °C and 80% relative humidity). Although the coarsening rate was relatively slow because of the low temperature (from 5.6 nm in the as-deposited state to ~7 nm after 30 h), it was identified that at 100 °C without humidity the Au nanoparticles resulted in shape refinement whereas the high humidity at 20 °C induced self-organization of the nanoparticles into a monolayer. It was also found that annealing in both cases tended to segregate the lipid molecules from the nanoparticle array and forced the nanoparticles into a tighter area. In the case of the high-humidity sample, the lipid segregation eventually led to extensive coalescence of the Au nanoparticles.