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Author(s): Joong Hwan Bahng [sup.1] , Bongjun Yeom [sup.2] , Yichun Wang [sup.1] , Siu On Tung [sup.3] , J. Damon Hoff [sup.4] , Nicholas Kotov [sup.1] [sup.2] [sup.3] [sup.5] [...], Micrometre-sized particles covered with stiff, nanoscale spikes are shown to exhibit long-term colloidal stability in both hydrophilic and hydrophobic media, without the need for chemical coating, owing to the effect of the spikes on the contact area and, consequently, the force between the particles. A new way of forming colloidal suspensions The conventional way of persuading hydrophobic particles to form colloidal suspensions in water -- and hydrophilic particles to disperse in oil -- is to camouflage the particles chemically with surfactants, organic tethers, adsorbed polymers or other agents that impart affinity for the solvent. Joong Hwan Bahng et al. now show that surface corrugation provides a very effective alternative strategy for dispersing particles in a wide range of solvents. The team produce micrometre-sized 'hedgehog' particles that are coated with stiff nanospikes and exhibit long-term colloidal stability in both hydrophilic and hydrophobic media. This unusual dispersion behaviour challenges current theories and deepens our understanding of colloidal interparticle interactions. The technique may have technological uses, as it provides particles that function in both organic and aqueous media. 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.sup.1,2. A different strategy for modulating the interaction between a solid and a liquid uses surface corrugation, which gives rise to unique wetting behaviour.sup.3,4,5. 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.

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 [...]

Author(s): David Chandler (corresponding author) [1] Most general chemistry students are taught how detergent removes grease. An essential aspect of this process depends on the amphiphilic nature of the detergent [...]

Author(s): Philip Ball [1] Water is notorious for behaving strangely, but it is possible that we don't yet know the half of it. Amid the crush of biological macromolecules and [...]

Author(s): Seema Singh [1]; Jack Houston [1]; Frank van Swol [1, 2]; C. Jeffrey Brinker (corresponding author) [1, 2] Long-range hydrophobic interactions operating underwater are important in the mediation of [...]