Superhydrophobicity comes from the amplification of surface chemistry effects by the small-scale roughness of the surface. A surface that is water-fearing becomes super water-fearing when it is made into a foam, but if that water-fearing surface chemistry can be switched off the foam becomes a super-sponge.
A water drop rests on top of a superhydrophobic surface (with a high contact angle).
When superhydrophobicity is turned off, the droplet is absorbed into the sponge.
In these experiments the hydrophobic surface chemistry is switched off by heating the foam above a designed-in trigger temperature. The image above left shows a droplet of water (with a pink food dye) on a superhydrophobic foam. On the right is the same foam, which looked no different until a droplet of water was deposited and slurped up. The switching can be designed to be triggered by many physical effects and not just heat exposure – the material becomes a simple indicator of the environment.
Read more about these experiments in the publication list below. This effect is described by Nature as a super-sponge with a super-slurp.
- Porous materials show superhydrophobic to superhydrophilic switching
N.J. Shirtcliffe, G. McHale, M.I. Newton, C.C. Perry and P. Roach, Chem. Comm. 25 (2005) 3135-3137
(see also Nature Highlight/News “Quick change for super sponge, published online 20-July-2005, front cover image.)
- Super-hydrophobic and super-wetting surfaces: Analytical potential?
G. McHale, M.I. Newton and N.J. Shirtcliffe, Analyst 129 (4) (2004) 284-287
- Superhydrophobic to superhydrophilic transitions of sol-gel films for temperature, alcohol or surfactant measurement
N.J. Shirtcliffe, G. McHale, M.I. Newton C.C. Perry and P. Roach, Maters. Chem. & Phys. 103 (1) (2007) 112-117