Adsorption of Intact Cubic Liquid Crystalline Nanoparticles on Hydrophilic Surfaces: Lateral Organization, Interfacial Stability, Layer Structure, and Interaction Mechanism

Liquid crystalline cubic phase nanoparticles (known as Cubosome), based on glycerol monooleate and stabilized by a nonionic block copolymer (Pluronic F-127), adsorb intact on hydrophilic silica in the presence of an electrolyte, except at high pH. To characterize the nature of the interaction, four techniques were applied in situ: fluorescence microscopy, quartz crystal microbalance with dissipation monitoring, neutron reflectivity, and null ellipsometry. The surface binding process occurs with no lateral ordering. There is no indication of collapse and spreading of the particles over a period of several hours. Even over much longer time scales (>45 h), there is no sign of relaxation or transition of the cubic phase internal structure of the adsorbed nanoparticles. Measurements of the adsorption kinetics with respect to three physical parameters allow us to propose an interaction mechanism where residual free polymer molecules present in the nanoparticle dispersions adsorb rapidly to the surface, and the nanoparticles adsorb more slowly in the gaps. The adsorption process is discussed as an interplay between repulsive and attractive forces, involving both the lipid and polymer components of the nanoparticles as well as the charge on the silica surface.