(605h) Modulating the Contact Angle between Non-Polar Polymers and SiO2 Nanoparticles

Polymer-nanoparticle interactions play an important role in polymer nanocomposites as well as polymeric reactions involving heterogeneous catalysts. There is a lack of effective quantification of polymer-nanoparticle interactions; instead, qualitative terms such as “weakly-interacting” or “strongly-interacting” are commonly used to describe the strength of interactions between polymer and nanoparticles. Here, we present an effective way to quantify these interactions by directly measuring the polymer-nanoparticle contact angle. Nanoparticles are sparsely coated on polymer thin films and the sample is heated above the polymer’s melting point for long durations, allowing the nanoparticles to equilibrate at the polymer-air interface. The height of the nanoparticle above the interface is measured using atomic force microscopy (AFM) which is then used to calculate the polymer-nanoparticle contact angle. We study different non-polar polymers of interest such as polystyrene, polyethylene, and polycyclooctene and modify the surface chemistry of the nanoparticles using atomic layer deposition (ALD) and alkyl silanization. Our results demonstrate that there can be significant differences in polymer-nanoparticle interactions which can be attributed to differences in polarity of the polymers and solid surface chemistry. We observe that polycyclooctene has stronger interactions with most metal oxides as compared to fully-hydrogenated polycyclooctene. However, this trend gets reversed when we do alkyl silanization of the silica nanoparticles, making the solid surface more non-polar. These differences in interactions can be leveraged to make polymer nanocomposites with unique properties and enable selective conversion of polymers without the need for separations in catalytic polymer reactions.