An engineered directional nanofilm mimics nature's curious feats

October 29, 2010
Insects like this water strider inspire a new nanotech coating. (credit: shutterstock.com)

(PhysOrg.com) -- In nature, textured surfaces provide some plants the ability to trap insects and pollen, certain insects the ability to walk on water, and the gecko the ability to climb walls. Being able to mimic these features at a larger scale would spur new advances in renewable energy and medicine. In a paper published in the October 10 issue of Nature Materials, a team of researchers from Penn State, the Naval Research Laboratory, and Harvard Medical School report on the development of an engineered thin film that mimics the natural abilities of water striding insects to walk on the surface of water, and for butterflies to shed water from their wings.

Although superhydrophobic self-cleaning surfaces are an active area of research, this development marks an engineering breakthrough in the ability to control the directionality of liquid transport. Using an array of poly(p-xylylene) nanorods synthesized by a bottom-up vapor-phase technique, the researchers were able to pin water droplets in one direction with enormous adhesive forces proportional to the number of nanorods and the , while releasing droplets in the opposite direction.

The differential between the pin and release force is 80 micronewtons, over ten times the values reported in other engineered surfaces with ratchet-like features, and the first such surface to be engineered at the nanoscale. Recently, the authors also demonstrated directional adhesion and friction of these surfaces, similar to the way a gecko can climb a wall (J. Applied Physics, 2010). Gecko’s feet contain approximately 4 million hairs per square millimeter, whereas polymer nanorods can be deposited at 40 million rods per square millimeter.

The nanofilm produced by this technique, called oblique angle deposition, provides a microscale smooth surface for the transport of small without pumps or optical waves and with minimal deformation for self-powered microfluidic devices for medicine and for microassembly.

In work sponsored by the U.S. Navy, the nanofilm is envisioned for use as a coating that would reduce drag on the hull of vessels and retard fouling. Potential industrial and energy related uses are as directional syringes and fluid diodes, pump-free digital fluidic devices, increased efficiency of thermal cooling for microchips, coatings for tires, and even in energy production from rain drops.

The lead on the Penn State team, Melik Demirel, associate professor of engineering science and mechanics and corresponding author on the report, believes that the current laboratory based technique, which although relatively simple still requires a vacuum, can be replaced by a liquid phase technique, which would allow for scaling the production of their material to industry size. “The major impact of our method is that for the first time we can create a controlled directional surface at the ,” Demirel concludes.

Explore further: New nano technique significantly boosts boiling efficiency

More information: The paper, “An engineered anisotropic nanofilm with unidirectional wetting properties,” is available at www.nature.com/nmat/journal/vaop/ncurrent/abs/nmat2864.html .

Related Stories

Secrets of the gecko foot help robot climb (w/ Video)

August 24, 2010

(PhysOrg.com) -- The science behind gecko toes holds the answer to a dry adhesive that provides an ideal grip for robot feet. Stanford mechanical engineer Mark Cutkosky is using the new material, based on the structure of ...

Bouncing water droplets reveal small-scale beauty (w/ Video)

October 14, 2010

In the video below, scientists have captured the simple movements of water droplets on a superhydrophobic carbon nanotube surface. The video shows the water droplets as they bounce, slide, and roll across different structures ...

Recommended for you

Graphene under pressure

August 25, 2016

Small balloons made from one-atom-thick material graphene can withstand enormous pressures, much higher than those at the bottom of the deepest ocean, scientists at the University of Manchester report.

Designing ultrasound tools with Lego-like proteins

August 25, 2016

Ultrasound imaging is used around the world to help visualize developing babies and diagnose disease. Sound waves bounce off the tissues, revealing their different densities and shapes. The next step in ultrasound technology ...

Nanovesicles in predictable shapes

August 25, 2016

Beads, disks, bowls and rods: scientists at Radboud University have demonstrated the first methodological approach to control the shapes of nanovesicles. This opens doors for the use of nanovesicles in biomedical applications, ...

Neuromorphic computing mimics important brain feature

August 18, 2016

(Phys.org)—When you hear a sound, only some of the neurons in the auditory cortex of your brain are activated. This is because every auditory neuron is tuned to a certain range of sound, so that each neuron is more sensitive ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.