A newly developed self-assembling polymer film that bends and stretches when hit by light is pointing the way to a new family of functional materials. This flexing film is the first material to have been made by coaxing complex molecules to form large-scale, highly ordered 3D arrays - a discovery that could change the way that many active materials are made, from artificial muscles to solar cells.
Nobuhiko Hosono, Takuzo Aida, and colleagues at RIKEN Advanced Science Institute in Wako and the University of Tokyo developed the self-assembly protocol. The trick to making the material is to heat it between two sheets of Teflon that have been drawn tight in one direction. This tension orients the Teflon sheets' internal structure along a single axis, which acts as a template for the molten polymer brushes sandwiched in between. The side chains of the polymer brush align with the Teflon, pulling each brush upright. As each polymer brush aligns in the same way, it forms a repeating 3D array.
Researchers used this photoisomerization behavior to confirm the remarkable long-range order of the polymer structure. The researchers expect the technique to work for other polymer brushes in similar side chains. To improve the artificial muscle-like behavior of their polymer film, Hosono says the team will try cross-linking the polymer side chains. This will prevent the molecular structure from becoming disordered as the polymer repeatedly curls and relaxes over many cycles, giving the muscle a longer lifetime.
