Light Controls Surface-Charging | September 17, 2010 Issue - Vol. 88 Issue 39 | Chemical & Engineering News
Volume 88 Issue 39 | p. 13 | News of The Week
Issue Date: September 17, 2010

Light Controls Surface-Charging

Electrostatics: Method could reveal mechanism of ubiquitous phenomenon behind static cling, copy machines
Department: Science & Technology
Keywords: contact electrification, triboelectric charging, surface science, polymers, electrostatics
Polymers with spiropyran groups reversibly form zwitterionic merocyanines when exposed to UV light, changing the polymer’s contact electrification properties in the process.
Polymers with spiropyran groups reversibly form zwitterionic merocyanines when exposed to UV light, changing the polymer’s contact electrification properties in the process.

A strategy using light to control contact electrification paves the way for better understanding of the phenomenon, which underlies processes such as static cling, laser printing, and the production of cleaner-burning coal.

Contact electrification—also known as triboelectric charging—is the electric charge that builds up on surfaces when they rub together and then separate. This built-up charge is what makes a balloon stick to a wall after it has been rubbed on your hair and what makes your socks stick to your pants when they come out of the dryer.

Despite the phenomenon's ubiquity, "scientific understanding of triboelectric charging is extremely poor," says Daniel J. Lacks of Case Western Reserve University. "Even the most basic questions are not understood. For example, it is not clear whether the charge that is transferred is carried by electrons or ions."

The study of triboelectric charging has been hampered by scientists' inability to reproduce the effect quantitatively, explains Samuel W. Thomas III of Tufts University. The method he and postdoc Simone Friedle have designed should fill that gap, he says. The researchers use light to reversibly alter the chemical composition of a surface such that the sign of the electric charge left on a steel ball changes after the ball rubs with the modified surface (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201003985).

"This development of a method to change triboelectric charging so reproducibly may be the key to further experiments that definitively determine what type of species is being transferred in the charging process," Lacks says.

Thomas also thinks the strategy might someday lead to electrostatic-driven actuators or ways to prevent potentially damaging static discharge in electronics manufacturing or fueling stations.

In the experiments, a steel ball rolls in a circular pattern on a film made of a spiropyran-based photoreactive polymer. As the ball rolls, it periodically passes over an electrode that measures the charge the ball builds up in real time.

The researchers find that the spiropyran film reversibly changes contact electrification behavior when exposed to ultraviolet light, which converts the film's spiropyran groups to less hydrophobic merocyanine groups. The ball charges positively when rolling on the spiropyran film, but negatively when rolling on the merocyanine film. Visible light reverses the effect, Thomas says.

The results suggest that a surface's hydrophobicity may play a role in contact electrification behavior, Thomas adds. His group is now designing other organic photochromic films with switchable redox potentials, electronic states, and hydrophobicities in hopes of sorting out which charged species migrate during contact electrification.

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kees de vos (June 15, 2018 12:33 AM)
In physics there is a almost unbelievable mistake right at the beginning. Repelling forces do not exist in the way everyone takes for granted. When magnets exert their magnetic fieldlines, it is their "equipment" to align as perfectly possible surrounding other magnetic fields. The first thing that happens is adapting their polarity. An easy example are small magnets which can easily change their position before any actual repelling exerts a retracting movement on distances like 30 times their own thickness. Only forced by us "repelling" becomes "obvious". When opposed poles approach, the magnetic field of each of the magnets looks for its own other pole instead of the opposing magnet's field, which ends up in changing it's (material) position. Electrons have a potential to react on elctrical fields as well as magnetic fields. Only ATTRACTION matters and atoms are built for that.
The situation for electricity is even more weard since it is very simple to discover a whole bunch of complete contradictions. When charging a sphere with electrons, one has to admit and sea clearly that electrons are attracted by the sphere since otherwise that couldn't be a charge-builtup to sustain. What in heaven's name history disguised, is that mainstream physics "explains" that the field opposes this attraction by being repelled. A full blown contradiction to my mind. Off course when the charge on the sphere gets high enough, electrons will wish for other places with fewer likewise charges. But like with the magnetic forcelines, ATTRACTION is the explanation. It is sin not to investigate these socalled repelling forces. Two big metal round plates of 1 m2 will suffice to make all clear. When one locates a probe charge somewhere in the middle of these plates (close to each other) and all three charges are the same NOTHING happens (untill one approaches the outer part around them other fields will start to influence. WHY was this not exercised and or discussed anywhere???
So this too changes attitudes towards gravity and especially the research upon which my reaction is based, for our earth is not zero by far concerning her electrical potential.
A first aid help should be the fact that all molecules (have to) share electrons and further the fact that all elements are electro negative (the quality to attract electrons) and there exists nothing like "electro positiveness"!!!!! No wonder we have lightnings by the millions.
Does everyone have to be fooled by the electrometer which is an instrument that enhances attractive forces by EARTHING it. The charges shown are ATTRACTED by the earth what is pretty plain knowledge. The electrical field is righteously defined as dependant on voltage differences and what when equally charged?; then there is no voltage difference and so no field and no fieldlines and no attraction. There is more to it but even a nobelprizewinner had no remarks of any failure but hell what could he do (let alone me!) Good luck and by the way; this all probably has to do with our zero which should never have been a number since it isn't, but we just made it so.

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