(654d) Stabilization of Colloidal Suspensions with a Bimodal Distribution of Microparticles and Nanoparticles

Charged nanoparticles have been found to enhance the stability of colloidal suspensions by forming a non-adsorbing nanoparticle layer surrounding larger neutral colloidal particles that induces an effective electrostatic repulsion. This stabilization mechanism is known as nanoparticle haloing. It has been previously shown that silica particles could be stabilized by this mechanism using highly charged zirconia nanoparticles at a low range of volume fractions. In this study we examined whether binary systems of silsesquioxane-zirconia and silsesquioxane-silica can develop nanohaloing. One of the advantages of using silsesquioxane compared to silicon is that they can be easily functionalized by fluorescent markers which is extremely valuable for imaging in confocal microscopy. The other advantage is that isoelectric point of silsequioxane is near the neutral pH while isoelectric point of silica is around pH 1.5. These advantages make silsesquioxane more favorable for conditions where highly acidic solutions cannot be used due to materials or safety concerns.

The charging behavior of the microspheres and the effect of the nanoparticles on the overall charge of the system have been studied. Ground results showed that silsesquioxane-zirconia system was stable at pH=4.5 where particles were highly charged and it was unstable near the isoelectric point of microspheres. Our results were in agreement with the recent results obtained from similar experiments performed onboard the ISS. Considering that both silsesquioxane microspheres and zirconia nanoparticles had similar electrostatic behavior, nanohaloing was not observed in this system. Based on these results, this study was aimed to identify an optimized binary system to be used in a future experiments on board the International Space Station.