Catching up with Nature - Breathlessly!

Pitcher plant (courtesy :Wikipedia)

SLIPS Technologies Inc.  a company anchored at Cambridge , Massachusetts, is barely a year old. Unusually slippery surface of the pitcher  plant inspired a group of researchers and that is the genesis of this company.  SLIPS is the acronym for Slippery Liquid Infused Porous Surface. The concept of a slippery surface which repels everything and anything was proven and reported   in a  research paper published  Nature in 2011. And in fact we covered it here.  Now  SLIPS Technologies Inc  is all set to market their products. To quote from their website- omniphobic surface  with optical transparence, scratch resistance, self-repair and self-cleaning characteristics that can operate under extreme environmental conditions.  

So what is the chemistry? Teflon and teflon coated non-stick vessels are household word now.  SLIPS uses similar materials from the vast family of  perfluorohydrocarbons for surface modification.  For example for medical devices undergo a two step surface coating process.  First a mono layer of teflon  is chemically grafted onto the device surface, which is then impregnated with a layer of another liquid perfluorocarbon. Such treated surfaces are called TLP  surfaces. (Tethered -Liquid Perflurocarbon surface). The super slippery surface of TLP treated medical devices  doesn't encourage blood clotting because neither fibrin nor platelets can adhere to the surface. For the same reason nor can bacteria form biofilm.(1,2)
  

Lotus leaf in water -Courtesy: Wikipedia

Scientists also marvel at the water repellence (super hydrophobicity) and self cleaning properties of the lotus leaf.  Water droplets get tossed around on the leaf surface and often aggregate to form bigger droplets and with the slightest tilt  falls off the leaf. But while  being tossed around,  the droplet would have smeared  all the dirt on itself and thus gently wiped the surface clean. Studies have  revealed that wax coated micro/nano "pimples" on the leaf surface drive  this unique phenomena.  Lotus effect has been recreated and replicated  on nano patterned surfaces. 

Now  Lu et al have  added  another innovative dimension to this effort. Their research paper appeared in the 6th March issue of Science(3). Super hydrophobic surfaces so far developed are mechanically  fragile and their performance graph dip when contaminated with  oil.  Liu and team have come up with an elegant  solution in the form of a paint formulation. Titanium dioxide nano particles coated with perfluorooctyltriethoxysilane is dispersed in ethanol.  Any surface, big or small can be coated  with this paint. Multiple coating techniques can be adopted: spraying, dip-coating, spin coating, extrusion- you name it.  The assorted titanium nanoparticles in the paint film take on the role of the "surface pimples". For the paint film to  stick strongly to the surface, a suitable  adhesive can be added to the formulation.  The robustness of the film  even after repeated exposure rough weather such "40 abrasion cycles with  sand paper " has been demonstrated on surfaces of  glass, cotton wool, steel, and filter paper. 

On one count the lotus leaf and pitcher plant still score high : Breathability.  Hold your breath- we will soon be getting there.  

References: 

1. Bioinspired coating for medical devices repel blood and bacteria
2. Literally nothing will stick to this new slippery surface
3. Robust self-cleaning surfaces that function when exposed to either air or oil: Lu eta al  
Science Vol. 347, issue 6226, pp 1132-5, 2015.