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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 raon 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 crosslinked with glutaraldehyde. Tunable broadband scattering is observed upon partial removal of the ZnO with complete removal resulting in semi-rigid 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 topography.

A variety of inorganic nanoscale materials produce microscale particles with highly corrugated geometries, but the mechanism of their formation remains unknown. Here we found that uniformly sized CdS-based hedgehog particles (HPs) self-assemble from polydisperse nanoparticles (NPs) with diameters of 1.0-4.0 nm. The typical diameters of HPs and spikes are 1770 ± 180 and 28 ± 3 nm, respectively. Depending on the temperature, solvent, and reaction times, the NPs self-assemble into nanorods, nanorod aggregates, low-corrugation particles, and other HP-related particles with complexity indexes ranging from 0 to 23.7. We show that "hedgehog", other geometries, and topologies of highly corrugated particles originate from the thermodynamic preference of polydisperse NPs to attach to the growing nanoscale cluster when electrostatic repulsion competes with van der Waals attraction. Theoretical models and simulations of the self-assembly accounting for the competition of attractive and repulsive interactions in electrolytes accurately describe particle morphology, growth stages, and the spectrum of observed products. When kinetic parameters are included in the models, the formation of corrugated particles with surfaces decorated by nanosheets, known as flower-like particles, were theoretically predicted and experimentally observed. The generality of the proposed mechanism was demonstrated for the formation of mixed HPs via a combination of CdS and Co3O4 NPs. With unusually high dispersion stability of HPs in unfavorable solvents including liquid CO2, mechanistic insights into HP formation are essential for their structural adaptation for applications from energy storage, catalysis, water treatment, and others.

High ionic strength environments can profoundly influence catalytic reactions involving charged species. However, control of selectivity and yield of heterogeneous catalytic reactions involving nano- and microscale colloids remains hypothetical because high ionic strength leads to aggregation of particle dispersions. Here we show that microscale hedgehog particles (HPs) with semiconductor nanoscale spikes display enhanced stability in solutions of monovalent/divalent salts in both aqueous and hydrophobic media. HPs enable tuning of photocatalytic reactions toward high-value products by adding concentrated inert salts to amplify local electrical fields in agreement with Derjaguin, Landau, Verwey, and Overbeek theory. After optimization of HP geometry for a model photocatalytic reaction, we show that high salt conditions increase the yield of HP-facilitated photooxidation of 2-phenoxy-1-phenylethanol to benzaldehyde and 2-phenoxyacetophenone by 6 and 35 times, respectively. Depending on salinity, electrical fields at the HP-media interface increase from 1.7 × 104 V/m to 8.5 × 107 V/m, with high fields favoring products generated via intermediate cation radicals rather than neutral species. Electron transfer rates were modulated by varying the ionic strength, which affords a convenient and hardly used reaction pathway for engineering a multitude of redox reactions including those involved in the environmental remediation of briny and salty water.

Hedgehog particles (HPs) replicating the spiky geometry of pollen grains revealed surprisingly high dispersion stability regardless of whether their hydrophobicity/hydrophilicity matches that of the media or not. This property designated as omnidispersibility is attributed to the drastic reduction of van der Waals interactions between particles coated with stiff nanoscale spikes as compared to particles of the same dimensions with smooth surfaces. One may hypothesize but it remains unknown, however, whether HPs modified with polymers or nanoparticles (NPs) would retain this property. Surface modifications of the spikes will expand the functionalities of HPs, making possible their utilization as omnidispersible carriers. Here, we show that HPs carrying dense conformal coatings made by layer-by-layer (LBL/LbL) assembly maintain dispersion stability in environments of extreme polarity and ionic strength. HPs, surface-modified by multilayers of polymers and gold NPs, are capable of surface-enhanced Raman scattering (SERS) and overcome the limited colloidal stability of other SERS probes. The agglomeration resilience of HPs leads to a greater than one order of magnitude increase of SERS intensity as compared to colloids with smooth surfaces and enables simultaneous detection of several targets in complex media with high ionic strength. Omnidispersible optically active colloids open the door for rapid multiplexed SERS analysis in biological fluids and other applications.