The structure of the polymer brush
The structure of the polymer brush
[Click to enlarge image]

Riken, a Japan-based research institute, developed a polymer film material that mechanically moves when light is shed on it.

The material is a kind of "polymer brush," which has a structure in which a main chain densely branches into long side chains. The material was made into a film by embedding Azobenzene molecules (compounds with a structure in which two benzene rings are connected by two nitrogen atoms), whose structure is changed by light, in its side chains and applying heat and pressure (hot press method).

When an ultraviolet ray (wavelength: 360nm) was applied, the film was significantly bent. And when a visible light (wavelength: 480nm) was applied, the film returned to the original shape.

Specifically, after polymer brushes having Azobenzene molecules in their side chains were heated to 130°C, they were left at a temperature of 115°C for about an hour. Then, they were cooled down to a room temperature to be made into a film measuring 5mm (W) x 6mm (L) x 10μm (H).

In the process of the hot press, the film was sandwiched by polytetrafluoroethylene (PTFE) sheets, which improve the degree of detachment, so that the orientations of the polymer brushes become the same. Because the Azobenzene molecules' impalpable structure change caused by light irradiation occurs in the same orientation, the film is bent.

Riken examined the cause of this special orientation structure of the polymer material by using the "Spring-8" large-scale radiation light facilities. As a result, it found that the polymer brushes detect the molecule orientation information of the one-dimensional carbon backbones located on the surfaces of the PTFE sheets and the polymer brushes form two-dimensional rectangular lattices in accord with the information, forming a regular three-dimensional accumulation structure.

The polymer material is expected to be applied to artificial muscles that move using light. Also, by applying the technology to regularly integrate functional molecules in a large area, it becomes possible to enable functional molecules to carry electrons from the top side of a film to the back side, making it possible to develop high-efficiency organic thin-film photovoltaic cells, Riken said.