A new kind of polymer is able to move independently under the influence of violet light. Developed by scientists from both TU Eindhoven and US Kent State University, the material can create a continuous wave motion under the influence of light, allowing the material to move independently.
The researchers report this in an article in the scientific journal Nature, published on 29 June. The new type of polymer has been clamped into a small rectangular frame by the researchers. As soon as the material is exposed, the polymer including frame goes 'walking'. In doing so, the researchers claim to have developed the first 'walking machine' that converts violet light directly into locomotion and is powered by a single fixed light source.
Shrinking and expanding under the influence of light
The new polymer reacts strongly under the influence of violet light. As soon as the material is exposed, one side of the material shrinks, while the other side expands. This creates a bulge when exposed, which disappears as soon as the light is removed. Although the polymer appears transparent at first glance, it absorbs violet light almost completely. This means that a shadow is created behind the material.
Using this 'self-shadowing' effect, the researchers have managed to create a continuous wave motion. To do this, a strip of polymer is placed in a rectangular frame that is shorter than the strip of polymer, making the material convex by default. As soon as concentrated LED light is shone obliquely onto the material from the front, the exposed part of the polymer bulges downwards. This creates a dimple in the strip, which causes another piece of the material to lie in the light. This causes the process to repeat itself, the dimple continuing to move backwards, creating a continuous wave motion.
'Walking away' from light
This continuous wave motion causes the material to 'walk' away from the light. As soon as the material is turned around and thus the other side of the material is on top, the wave motion moves in the other direction and thus the 'walking machine' actually walks towards the light. The video below demonstrates how the material works.
The polymer used by the researchers is based on liquid crystals. This is a material known from liquid crystal displays (LCDs). By incorporating a fast-reacting and light-sensitive variant of this material into a liquid crystal polymer, the researchers have created a material that immediately deforms as soon as it is exposed to violet light and immediately bends back as soon as this light has disappeared.
Collaboration
The material was created by researchers from TU Eindhoven in collaboration with researchers from the US Kent State University. The empirical research on the material took place in Eindhoven, while Kent State University developed the theoretical model. The research was made possible in part by grants from the Dutch research financier NWO and from the European Research Council.
Author: Wouter Hoeffnagel
Source: TU Eindhoven
Source: Kent State University
Photo by: Bart van Overbeeke
