Microscale Polarization Color Pixels from Liquid Crystal Elastomers

Liquid crystal elastomers (LCEs) attract burgeoning research interests due to their programmable 3D shape transformation and achievable large strain (up to 400%), which allow their diverse applications. One exciting application is soft microrobots towards biomedical applications. Here, it is demonstrated that polarization colors, an intrinsic property from the anisotropic nature of LCEs, can assist LCEs in their diverse applications. Microscale color pixels with sizes as small as 15 mu m x 15 mu m are obtained with designable colors from precisely controlled thicknesses enabled by two-photon polymerization technique. It is then demonstrated that in-plane rotation of LCE pixels only changes their color brightness instead of color hue and small tilting angle (<15 degrees) causes almost no change of their color. These properties enable high-contrast tracking of LCEs under polarized microscope. Furthermore, it is exhibited that both 2D and 3D microstructures with pre-designed multiple colors can be realized, allowing for LCE applications requiring precise discrimination of different components. Finally, dynamic polarization colors are explored by insertion of waveplates and change of temperature, which allows for either better tracking of LCEs or applications of LCEs in temperature sensing and information encryption. It is expected that polarization colors will assist various LCE applications, especially soft microrobot and art display applications.