December 10, 2015

Superhydrophobic coating protects without the price


An environmentally friendly superhydrophobic coating repels water as effectively as
commercial coatings that employ hazardous materials, according to scientists at Rice University and
the University of Swansea. (Credit: Shirin Alexander/University of Swansea)

(December 10, 2015)  ‘Green’ project led by Rice, Swansea scientists matches best water repellant. 

A new class of superhydrophobic nanomaterials might simplify the process of protecting surfaces from water.

A material made by scientists at Rice University, the University of Swansea, the University of Bristol and the University of Nice Sophia Antipolis is inexpensive, nontoxic and can be applied to a variety of surfaces via spray- or spin-coating.

The researchers led by Rice chemist Andrew Barron reported their find in the American Chemical Society journal ACS Applied Materials and Interfaces.

The hydrocarbon-based material may be a “green” replacement for costly, hazardous fluorocarbons commonly used for superhydrophobic applications, Barron said.

“Nature knows how to make these materials and stay environmentally friendly,” Barron said. “Our job has been to figure out how and why, and to emulate that.”

The lotus leaf was very much on their minds as the researchers tried to mimic one of the most hydrophobic — water-repelling — surfaces on the planet. Barron said the leaf’s abilities spring from its hierarchy of microscopic and nanoscale double structures.

“In the lotus leaf, these are due to papillae within the epidermis and epicuticular waxes on top,” he said. “In our material, there is a microstructure created by the agglomeration of alumina nanoparticles mimicking the papillae and the hyperbranched organic moieties simulating the effect of the epicuticular waxes.”

A scanning electron microscope image of a new superhydrophobic material shows
the rough surface of functionalized alumina nanoparticles. Scientists at Rice University
and the University of Swansea led the creation of the environmentally friendly material.
(Credit: University of Swansea)

Fabrication and testing of what the researchers call a branched hydrocarbon low-surface energy material (LSEM) were carried out by lead author Shirin Alexander, a research officer at the Energy Safety Research Institute at the Swansea University Bay Campus.

There, Alexander coated easily synthesized aluminum oxide nanoparticles with modified carboxylic acids that feature highly branched hydrocarbon chains. These spiky chains are the first line of defense against water, making the surface rough. This roughness, a characteristic of hydrophobic materials, traps a layer of air and minimizes contact between the surface and water droplets, which allows them to slide off.

video >>