title: Anomalous dispersions of 'hedgehog' particles.
abstract: Hydrophobic particles in water and hydrophilic particles in oil aggregate, but can form colloidal dispersions if their surfaces are chemically camouflaged with surfactants, organic tethers, adsorbed polymers or other particles that impart affinity for the solvent and increase interparticle repulsion. A different strategy for modulating the interaction between a solid and a liquid uses surface corrugation, which gives rise to unique wetting behaviour. Here we show that this topographical effect can also be used to disperse particles in a wide range of solvents without recourse to chemicals to camouflage the particles' surfaces: we produce micrometre-sized particles that are coated with stiff, nanoscale spikes and exhibit long-term colloidal stability in both hydrophilic and hydrophobic media. We find that these 'hedgehog' particles do not interpenetrate each other with their spikes, which markedly decreases the contact area between the particles and, therefore, the attractive forces between them. The trapping of air in aqueous dispersions, solvent autoionization at highly developed interfaces, and long-range electrostatic repulsion in organic media also contribute to the colloidal stability of our particles. The unusual dispersion behaviour of our hedgehog particles, overturning the notion that like dissolves like, might help to mitigate adverse environmental effects of the use of surfactants and volatile organic solvents, and deepens our understanding of interparticle interactions and nanoscale colloidal chemistry.
authors: Department of Biomedical Engineering, University of Michigan, 1107 Carl A. Gerstacker Building, 2200 Bonisteel Boulevard, Ann Arbor, Michigan 48109, USA.
authors: Joong Hwan
authors: JH
authors: Bahng
authors: Department of Chemical Engineering, University of Michigan, 3074 H.H. Dow Building, 2300 Hayward Street, Ann Arbor, Michigan 48109, USA.
authors: Bongjun
authors: B
authors: Yeom
authors: Department of Biomedical Engineering, University of Michigan, 1107 Carl A. Gerstacker Building, 2200 Bonisteel Boulevard, Ann Arbor, Michigan 48109, USA.
authors: Yichun
authors: Y
authors: Wang
authors: Macromolecular Science and Engineering Program, University of Michigan, 3062C H.H. Dow Building, 2300 Hayward Street, Ann Arbor, Michigan 48109, USA.
authors: Siu On
authors: SO
authors: Tung
authors: Single Molecule Analysis in Real Time (SMART) Center, Ann Arbor, Michigan 48109, USA.
authors: J Damon
authors: JD
authors: Hoff
authors: 1] Department of Biomedical Engineering, University of Michigan, 1107 Carl A. Gerstacker Building, 2200 Bonisteel Boulevard, Ann Arbor, Michigan 48109, USA [2] Department of Chemical Engineering, University of Michigan, 3074 H.H. Dow Building, 2300 Hayward Street, Ann Arbor, Michigan 48109, USA [3] Macromolecular Science and Engineering Program, University of Michigan, 3062C H.H. Dow Building, 2300 Hayward Street, Ann Arbor, Michigan 48109, USA [4] Department of Material Science and Engineering, University of Michigan, 3074 H.H. Dow Building, 2300 Hayward Street, Ann Arbor, Michigan 48109, USA [5] Biointerfaces Institute, University of Michigan, North Campus Research Complex, 2800 Plymouth Road, Ann Arbor, Michigan 48109, USA.
authors: Nicholas
authors: N
authors: Kotov
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