Tag Archives: electric charge

silk_flowing_spider

How spiders can fly for miles: electrostatic launching

silk_flowing_spider

Silk flows from a spiny-backed spider. Kunkel Microscopy, Inc./Visuals Unlimited, Inc./Corbis

In a mind boggling act, spiders are capable of “ballooning” themselves using silk strands and fly for miles, both in altitude and distance. Small and big spiders alike can do this, although smaller ones are capable of traveling further, and scientists have long theorized the mechanisms of spider ‘flight’. Peter Gorham at the University of Hawaii tested a theory that dates back from the early 1800s, first proposed by Charles Darwin himself, which states that the spiders achieve their amazing lift through electrostatic means. His findings support this theory, explaining the mysterious and peculiar spider flight behavior which has puzzled scientists for so long.

While off the cost of Argentina a few tens of miles away sailing in the infamous HMS Beagle in the 1830s, Darwin perplexedly recalled how the ship was flooded with spiders as if they had dropped from the clouds.

“I repeatedly observed the same kind of small spider, either when placed or having crawled on some little eminence, elevate its abdomen, send forth a thread, and then sail away horizontally, but with a rapidity which was quite unaccountable.”  C. Darwin.

At the time Darwin thought spiders used their silk to catch thermal air currents to carry them to considerable height, and this conventional wisdom was used to explain it for years. Darwin also proposed  “electrostatic repulsion” played a role in the fanning of the threads, but this theory was dismissed by biologists in favor of the thermal air currents theory.

Launching spiders  several miles up high

Hot air doesn’t account for a number of anomalies, however.  How can these spiders launch themselves with a surprisingly high velocity even when there is little or no wind; how do thermal currents lift heavy adult spiders of up to 100 milligrams; and when spiders release several threads, why do these threads form a fan-shape as if repelling each other?

Gorham re-examined the electrostatic theory and says that it can easily account for all the mysterious flying behaviours of ballooning spiders. He first explored the idea by find out how much charge a strand must have to lift a spider of a certain weight. This turns out to range from 10 to 30 nanoCoulombs. Spider silk contains certain charge bearing amino acids and becomes negatively charged when put in contact with other materials. In theory, then, spider silk could become charge right from its release as it leaves the spinnerets, through a process known as flow electrification.

“There are thus a wide and plausible range of processes by which the strands can acquire initial charge,” Gorham writes.

As for the origin of this charge, Gorham believes the Earth itself could offer the necessary kick. The Earth has as a negative charge density of about 6 nanoCoulombs per square metre on average or more than enough give spider silk the necessary boost.  All this explains the spider’s launch power in still air, why large spiders can get such a lift and why the silk strands fan out: “because their negative charges repel.”

via Nat Geographic

single molecule electric charge imaging

IBM images electric charge distribution in a SINGLE molecule – world’s first!

Part of a the recent slew of revolutionary technological and scientific novelties coming off IBM‘s research and development lab, the company has just announced that it has successfully managed to  measure and image for the first time how charge is distributed within a single molecule. The achievement was made possible after a new technique, called Kelvin probe force microscopy (KPFM), was developed. Scientists involved in the project claim that the research introduces the possibility of imaging the charge distribution within functional molecular structures, which hold great promise for future applications such as solar photoconversion, energy storage, or molecular scale computing devices. Until now it has not been possible to image the charge distribution within a single molecule.

single molecule electric charge imaging The team, comprised of scientists Fabian Mohn, Leo Gross, Nikolaj Moll and Gerhard Meyer of IBM Research, Zurich, imaged the charge distribution within a single naphthalocyanine molecule using what’s called Kelvin probe force microscopy at low temperatures and in ultrahigh vacuum – these conditions were imperative, as a high degree of thermal and mechanical stability and atomic precision of the instrument was required over the course of the experiment, which lasted several days.

Derived off the revolutionary atomic force microscopy (AFM), the KPFM measures the potential difference between the scanning probe tip and a conductive sample, in our case the naphthalocyanine molecule – a cross-shaped symmetric organic molecule. Therefore, KPFM does not measure the electric charge in the molecule directly, but rather the electric field generated by this charge.

“This work demonstrates an important new capability of being able to directly measure how charge arranges itself within an individual molecule,” says Michael Crommie, professor for condensed matter physics at the University of Berkeley.

“Understanding this kind of charge distribution is critical for understanding how molecules work in different environments. I expect this technique to have an especially important future impact on the many areas where physics, chemistry, and biology intersect.”

The potential field is stronger above areas of the molecule that are charged, leading to a greater KPFM signal. Furthermore, oppositely charged areas yield a different contrast because the direction of the electric field is reversed. This leads to the light and dark areas in the micrograph (or red and blue areas in colored ones).

The new KPFM technique promises to offer complementary information about a studied molecule, providing valuable electric charge data, in addition to those rendered by scanning tunneling microscopy (STM) or atomic force microscopy (AFM). Since their introduction in 1980′, STM, which images electron orbitals of a molecule, and ATM, which resolves molecular structure, have become instrumental to any atomic and molecular scale research today, practically opening the door to the nanotech age. Maybe not that surprisingly, the STM was developed in the same IBM research center in Zurich, 30 years ago.

“The present work marks an important step in our long term effort on controlling and exploring molecular systems at the atomic scale with scanning probe microscopy,” Gerhard Meyer, a senior IBM scientist who leads the STM and AFM research activities at IBM Research – Zurich.

The findings were published in the journal Nature Nanotechnology. 

Source / image via IBM