Electricity driving force behind macro-motor
A team from the University of Twente in the Netherlands has succeeded in manufacturing a macro-sized engine. The molecular motor is capable of turning chemical energy into movement in the same way a steam engine turns heat energy into movement. This synthetic motor stretches and shrinks by reduction/oxidation, stretching a synthetic polymer by up to 47nm (47 millionths of a metre). This is, of course, not a great distance, but this is the first time some of the molecular 'engines' that occur in nature have been adequately modelled on a similar scale. The process works with a particular synthetic polymer, known as PFS (poly-ferrocenydimethylsilane), which occurs in 'chains' or 'clumps', rather than straight lines, rather like a broken and tangled spring. Iron is added to the polymer, which is then oxidised and reduced (electrons lost and then added) using electrical current. The polymer extends when the iron molecule loses an electron, gaining a positive charge. 'The polymer chains bear positive charges that are distributed along their length [...] it is expected that the electrostatic interactions between the charges along the polymer chain increase the distances between like-charged segments, i.e. it favours the stretched conformation of the chains,' reads the paper. In other words, when the molecule is positively charged, then the polymer chains repel one another and are pushed outwards. When the electron returns and the system becomes electrically neutral again, then the chains return to their former shape. The motor has been found to have an efficiency of 5 per cent, and has significant advantages over previous types of macro-motor. Firstly, the system is fully reversible, and secondly, the level of control is very high. Previous forms of motor have relied on the action of light to produce the motor effect, but this motor is smaller than a light wavelength and so cannot be seen. Because the macromotor can be very precisely placed and the current accurately applied, the macromotor could easily be used in future macro- or nano-devices. Because the macromotor is far too small to be seen, measurements were taken using an Atomic Force Microscope.
Countries
Netherlands