Microscale Polarization Color Pixels from Liquid Crystal Elastomers

Abstract

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 µm × 15 µm 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°) 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.

Temperature‐Responsive 4D Liquid Crystal Microactuators Fabricated by Direct Laser Writing by Two‐Photon Polymerization

“…Such dark–bright states are associated with the presence of uniaxial alignment. [ 33,41,42 ] Thus, the mesogenic alignment of these microstructures is determined by the alignment layer in the cell construct and not by the fabrication parameters or the scanning direction. This allows for facile preprogrammed determination of the alignment in the structures by selection of appropriate alignment layers prior to fabrication.…”

“…These colors arise from the anisotropic optical property of LCs, defined as the difference between the extraordinary ( n e ) and ordinary ( n o ) refractive indices, also known as birefringence ( △n = n e – n o ). [ 33,41 ] When light travels through a uniaxially aligned LC sample with a specific thickness ( d ), it encounters an optical path difference (OPD = d △n ) between transmitted extraordinary and ordinary rays that results in a polarization color when observed between crossed polarizers. Thus, the colors are dependent on the structure's height and geometry.…”

The emerging technology of biohybrid micro-robots: a review

“…Faced with the defects of conventional rigid drivers, new driving methods via using flexible stimuli-active materials such as dielectric elastomer actuator (DEA) [24][25][26], shape memory alloy (SMA) [27][28][29], and liquid crystal elastomer (LCE) [30][31][32][33] are developed. For example, Wood's [34] team developed a flying robot driven by multilayer dielectric elastomers, which can perceive and withstand collision with obstacles and recover from collisions by taking advantage of the robustness of the material and the passive stability of the machine.…”

Liquid Crystal Elastomer‐Based Magnetic Composite Films for Reconfigurable Shape‐Morphing Soft Miniature Machines

“…[17] The concurrent emergence of contracting and expanding strains interplays with the bulk geometry to enable 2D and 3D shapemorphing, unlike other active materials, e.g., hydrogels [18] and shape memory polymers, [19][20][21] which require additional passive layers for shapemorphing. LCE is also superior to other responsive materials in terms of its optical characteristics [22] and high work densities with unusual force-displacement characteristics, [6,8,23,24] where 2D-to-2D, [17,25] 2D-to-3D, [26,27] and 3D-to-3D shape-transformations [15,[28][29][30] of LCE materials have been demonstrated. These capabilities and advantages of LCEs have been utilized to demonstrate actuators for a variety of soft-bodied robots [1,4,7,16,[31][32][33][34][35] and bioinspired devices, such as an artificial iris, [2,36] an artificial aquatic polyp, [37] and a microwalker.…”