New Look at Nature Through the Eyes of Physicists

Take a new look at nature through the eyes of physicists at next month's March Meeting of American Physical Society (APS), which takes place from March 16-20, 2009 at the David L. Lawrence Convention Center in Pittsburgh.

Many talks at the meeting will focus on animal locomotion and physiology: from the efficiency of trout swimming, to the wandering pattern of ants and the specially adapted ears of a lizard. Other talks look at the physical properties of new materials that are inspired by things in nature -- lotus leaf film, gecko tape, and fish-like sensors. Highlights of a few of these talks are described below.

LOTUS LEAF INSPIRES NEW MATERIALS
In ancient eastern art, the Buddha is often depicted seated upon a lotus leaf -- a longstanding symbol of purity because these leaves always seem clean, even while floating atop murky waters. The physical basis of this "lotus effect," as it sometimes called, arises from microscopic ridges on the surface of the leaf. These ridges have their own, much smaller nanoscale ridges, and the overall effect is to repel water as well as anything in nature.

Prof. Spiros H. Anastasiadis and his colleagues, at the Foundation for Research and Technology-Hellas and the University of Crete in Greece, have been designing artificial surfaces that mimic the natural properties of lotus leaves. They use lasers to etch a silicon surface in ways that mimic the ridges of the lotus leaf, and they synthesize polymers on top of the silicon ridges that further enhance their lotus-like properties. Because they are using polymers, Anastasiadis and his colleagues can also chemically manipulate their artificial lotus surfaces in a number of novel ways. One surface they created has a lotus effect that is tunable with pH -- water droplets fully wet a surface that was exposed to an acidic environment whereas they bounce off a surface that was exposed to a basic one. They are now working on polymers that are tunable with light, electricity, and humidity. These artificial surfaces with responsive surfaces can have a wide range of applications, in the development of self-cleaning surfaces, low friction coatings, water proof and anti-rain textiles, molecular sensors, micro- and nano-fluidics, lab-on-chip devices, etc. (Talk Y19.13, http://meetings.aps.org/Meeting/MAR09/Event/100250).

A NEW MATERIAL INSPIRED BY BLIND CAVE FISH
Many fish have tiny hair-like cells on their bellies and other parts of their bodies that collect sensory information on their surroundings, helping them navigate their underwater environments. The blind cave fish (named for obvious reasons) has a large number of these receptors, which compensate for its degenerated non-functioning eyes. The blind cave fish further enhances its ability to sense its surroundings by covering its flow receptors with a gel-like material, called a cupula. The cupula couples the motion of its receptors to the surrounding waters, greatly increasing their sensitivity.

Graduate Student Mike McConney and his colleagues at the Georgia Institute of Technology have now designed an artificial polymer that mimics this effect. The work builds upon an earlier invention by their collaborators at Northwestern University who constructed tiny microfabricated sensors that mimic the blind cave fish receptor. Last year McConney and Vladimir Tsukruk studied the physical properties of the blind cave fish cupula and created a jelly-like material that approximates it. When applied to the microsensors, the artificial polymer improved their sensitivity 40 times. (Talk Y20.6, http://meetings.aps.org/Meeting/MAR09/Event/100260).

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