Externally induced color‐ and shape‐changes in micrometer‐sized objects are of great interest in novel application fields such as optofluidics and microrobotics. In this work, light and temperature responsive micrometer‐sized structural color actuators based on cholesteric liquid‐crystalline (CLC) polymer particles are presented. The particles are synthesized by suspension polymerization using a reactive CLC monomer mixture having a light responsive azobenzene dye. The particles exhibit anisotropic spot‐like and arc‐like reflective colored domains ranging from red to blue. Electron microscopy reveals a multidirectional asymmetric arrangement of the cholesteric layers in the particles and numerical simulations elucidate the anisotropic optical properties. Upon light exposure, the particles show reversible asymmetric shape deformations combined with structural color changes. When the temperature is increased above the liquid crystal‐isotropic phase transition temperature of the particles, the deformation is followed by a reduction or disappearance of the reflection. Such dual light and temperature responsive structural color actuators are interesting for a variety of micrometer‐sized devices.

Electrically tunable lenses offer the possibility to control the focal distance by applying an electric field. Different liquid crystal tunable lenses have been demonstrated. In order to minimize lens aberrations, multi-electrode designs allow us to fine-tune the applied voltages for every possible focal distance. In this Letter, we provide a novel multi-electrode design in which only one lithography step is necessary, thereby offering a greatly simplified fabrication procedure compared to earlier proposed designs. The key factor is the use of a high-permittivity layer, in combination with floating electrodes.

A planar liquid crystal (LC) cell is developed in which two photo-alignment layers have been illuminated with respectively a horizontal and a vertical diffraction pattern of interfering left- and right-handed circularly polarized light. In the bulk of the cell, a complex LC configuration is obtained with periodicity in two dimensions. Remarkably, the period of the structure is larger than the period of the interference pattern, indicating that lowering of the symmetry allows a reduction in the elastic energy. The liquid crystal configuration depends on the periodicity of the alignment but also on the thickness of the cell. By applying a voltage over the electrodes, the power going into the different diffracted orders can be tuned. Finite element (FE) simulations based on Q-tensor theory are used to find the 3D equilibrium director distribution, which is used to simulate the near-field transmission profile based on the Jones calculus. A 2D Fourier transform is performed for both the x- and y-component of the transmitted wave to find the diffraction efficiency.

Patterned liquid crystal (LC) configurations find widespread applications in functional devices such as lenses, gratings, displays and soft-robots. In combination with external stimuli such as an applied electric field, photo-alignment at the surfaces offers an attractive way to stabilize different LC structures in the bulk of a device. Herein, a planar LC cell is developed using a photo-alignment layer at the bottom substrate and a rubbed nylon film at the top substrate. Patterned planar photo-alignment is achieved by modulating the linear polarization with a spatial light modulator (SLM) and projecting the pattern onto the bottom substrate. A ring pattern is written into the photo-alignment layer with a continuous rotation between an inner radius and an outer radius. In the other regions the alignment is parallel to the rubbing direction at the top substrate. Four different LC configurations are observed: structure A in which a ring-shaped region is formed with an out of plane (vertical) orientation perpendicular to the substrate, structure B which has a single disclination loop and a 180° twist at the inner region of the photo-patterned ring (r < r_in), structure C which has no discontinuities but a 360° twist in the inner region of the photo-patterned ring (r < r_in) and structure D with 2 disclination loops. The LC director configuration for all 4 structures is simulated through finite element (FE) Q-tensor simulations and the optical transmission for each structure is simulated using a generalized beam propagation method.

The formation of nematic liquid crystal (LC) superstructures in cells with non-uniform photo-alignment at the confining substrates is studied experimentally and by simulations. An interference pattern of left- and right-handed circularly polarized light is used to define the alignment at both substrates separately, so that the alignment varies along the x-coordinate on one substrate and along the y-coordinate on the other substrate. The interplay between the complex surface alignment and the liquid crystalline soft matter leads to the formation of interesting 3D configurations. The periodic LC structures that are formed in the bulk of the cell are analyzed experimentally by polarizing optical microscopy (POM) for different applied voltages. In the region with strong photo-alignment at both substrates, a 2D LC polarization grating (PG) with a complex 3D director configuration is formed. Distinct periodic structures with different symmetry properties are observed in the regions with weak illumination at the top and/or bottom substrate. The director configuration in the different regions was successfully simulated with the help of finite element (FE) Q-tensor simulations. The agreement between the simulations and the experiments was verified by comparing the POM images with simulated results for the transmission between crossed polarizers.