Omnidispersible Microscale Colloids with Nanoscale Polymeric Spikes

Abstract

Particle stability in a multiplicity of fluid environments is critical for colloids used in catalysis, sensing, and composites. Hedgehog particles (HPs), inspired by the spiky topology of pollen grains and viral capsids, enable dispersion stability regardless of whether their polarity matches that of the solvent. Previous implementations of HPs were all based on rigid spikes from inorganic materials, such as ZnO, whereas polymeric spikes offer a unique spectrum of optical, chemical, thermal, and mechanical properties including potential stimuli-responsive behavior. Microscale particles with nanoscale polymeric spikes referred to here as tendril particles were made by layer-by-layer assembly of polyallylamine films deposited onto rigid ZnO templates and then cross-linked with glutaraldehyde. Tunable broadband scattering is observed upon partial removal of the ZnO with complete removal resulting in semirigid hollow polymer sleeves. While being hydrophilic, they disperse in nonpolar media such as heptane and high ionic strength aqueous media. Gradual removal of ZnO nanorods affords spectral tuning of the near-infrared band associated with light scattering from the high refractive index spikes. The polymer spikes also allow for loading of cargo nanoparticles, molecules, and polymers. By adding poly(N-isopropylacrylamide-co-acrylic acid) subunits, controlled aggregation is observed in response to temperature. Structural integration of dopamine moieties into the layered films allows for controlled aggregation in response to alkaline conditions. The mechanical and structural flexibility of tendrils with sleeve-like morphology enables a new generation of multifunctional particles with properties controlled by their nanoscale surface topology.

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