\u201cWe believe our microactuator is more efficient and powerful than any current microscale actuation technology, including human muscle cells. What\u2019s more, it uses this very interesting material \u2014 vanadium dioxide \u2014and tells us more about the fundamental materials science of phase<\/a> transitions,\u201d<\/p><\/blockquote>\n says Junqiao Wu of UC Berkeley.<\/p>\n Wu and his colleagues came upon the microactuator idea by accident while studying an unrelated problem. Vanadium dioxide is a classic example of a strongly correlated material, one in which the behaviour of each electron is tied to its neighbouring electrons.<\/p>\n The exotic resulting electronic behaviours have made vanadium dioxide a subject of scientific investigation for decades, most of it focused on an unusual pair of phase transitions.<\/p>\n A single actuator curls and extends as the temperature is changed by 15 degrees Celsius, as shown in this micrograph. On right, a palm-like configuration of actuators all curl together, opening and closing like a tiny hand. The scale bar is 50 microns. When it is heated over 67 degrees Celsius, vanadium dioxide transforms from an insulator to a metal, together with a structural phase transition that shrivels the material in one dimension while expanding in the other two.<\/p>\n For decades, researchers have debated whether one of these phase transitions drives the other or if they are separate phenomena that coincidentally occur at the same temperature.<\/p>\nIndependent Phase Transitions<\/h2>\n
![\"v02](\"https:\/\/techfragments.com\/wp-content\/uploads\/2012\/12\/v02-actuator-curls.jpg\")
Credit: Wu, et al.<\/p><\/div>\n