Colloidosomes from the controlled interaction of submicrometer triglyceride droplets and hydrophilic silica nanoparticles

The self-assembly of hydrophilic silica nanoparticles at the surface of charged submicrometer triglyceride droplets has been investigated with the aim to optimize the preparation of stable colloidosomes. The droplet charge, oil phase volume fraction, droplet/nanoparticle ratio, and salt concentration play important roles in controlling nanoparticle interactions and are reflected in the colloidosome zeta potential, size, stability, and interfacial structure (visualized by freeze-fracture SEM). Silica nanoparticle interactions with negatively charged droplets are weak, and partially covered droplets are identified. Positively charged droplets are strongly coated by silica nanoparticles and undergo charge reversal at specific droplet to nanoparticle ratios and electrolyte concentrations. Droplets at volume fractions (varphi) <10 (-4) undergo time-dependent limited coalescence until nanoparticle coverage is complete. For varphi in the range 10 (-4) to 2.5 x 10 (-4) and at certain critical droplet to nanoparticle ratios, droplets undergo neutralization or charge reversal coupled with aggregation and precipitation; this occurs in a time-independent manner. Specific conditions have been identified where stable 1-3 mum colloidosomes can be phase separated from heterocoagulates of droplets and nanoparticles.