‘Hedgehog’ particles reveal surprisingly high dispersion stability regardless of whether or not their hydrophobicity or hydrophilicity matches that of their surrounding media. To some degree, they defy the well-known heuristics, “like dissolves like”. The deviation from this seemingly universal rule originates from the drastic reduction of van der Waals (dispersive) interactions between particles coated with stiff nanoscale spikes compared to particles of the same dimensions with smooth surfaces, thereby creating a precedent for a controlling ubiquitous dispersive interactions.
The topography of hedgehog particles and some other highly corrugated particles replicates the geometry of pollen grains, ocean plankton, viruses, and other examples of spiky particles found for different living organisms. In all of these examples, decoration of the particle’s surfaces with spikes serves the same purpose of controlling agglomeration and attachment processes needed for the proliferation of the corresponding species.
To date, we have demonstrated several types of hedgehog particles. Although they do not form indefinitely stable colloidal dispersions, all of them display markedly enhanced dispersibility regardless of the solvent polarity. The basic hedgehog particles are three micron in diameter with polymeric spherical cores on which ZnO spikes about 100 nm in diameter are grown. The synthesis of hedgehog particles was adapted to a continuous process in a commercial reactor allowing their pilot-scale production.
In singular yet foretelling cases we were also able to self-assemble hedgehog particles from nanoparticles. For example, uniform mesoscale iron diselenide (FeSe2) hedgehogs were made by one-pot self-assembly from 2-4 nm FeSe2 anisotropic nanoplatelets. Similarly, hedgehog particles with twisted spikes were assembled from chiral gold disulfide (AuS2) nanoplatelets. The complexity of the AuS2 hedgehogs enumerated by Graph Theory exceeds that of prototypical spiky particles synthesized by ocean plankton.
In ongoing projects, we address the following questions:
How complex hedgehog particle can be?
Can hedgehog particles serve as catalysts, especially in hydrophobic media?
What are the optical properties of hedgehog particles?
Similarly to the studies of nanoparticle self-assembly, these projects deepen our understanding of inter-particle forces. Answering these questions also opens the road for their various applications in chemical, energy, and biomedical technologies.