Three-dimensional actuators transformed from the programmed two-dimensional structures via bending, twisting and folding mechanisms

Combining the physical principle of actuators with the basic concept of photonic crystals, colour-tunable three-dimensional (3D) photonic actuators were successfully fabricated. By controlling the d-spacings and the refractive index contrasts of the self-assembled 3D colloidal photonic crystals, colours of the photonic actuators were tuned. Various shapes of these 3D actuating objects were constructed by transforming the programmed 2D structures via bending, twisting and folding mechanisms. These 2D structures were first programmed by breaking the symmetry. The selective swellings were then applied as driving forces to control the shapes and colours of the photonic actuators. Scroll photonic actuators had been first demonstrated by bending the traditional 2D cantilever structure (K.-U. Jeong, et al., J.Mater.Chem., 2009, 19, 1956). By breaking the symmetry of a cantilever structure perpendicular to its long axis, polypeptide-/DNA-like 3D helical photonic actuators were obtained from the programmed 2D structure via twisting processes. Both left- and right-handed scrolls and helices with various colours can be achieved by changing the polarity of solvents. Different types of 3D actuators, such as cube, pyramid and phlat ball, were also demonstrated via the folding mechanism. The reversible 3D photonic actuators transformed from the programmed 2D structures via the bending, twisting and folding mechanisms may be applied in the field of mechanical actuators, and optoelectronic and bio-mimetic devices.