Tunable gradient refractive index (GRIN) lens has attracted increasing attention from researchers due to its promising applicability in various optical and electronic applications. However, the polarization‐insensitive, large sized, and focal‐length‐controllable GRIN lens is highly difficult to implement due to the lack of available functional materials with the property of tunable refractive index. Herein, a two dimensional (2D) α‐ZrP nanocolloid is introduced to fabricate a GRIN lens in which the 2D nanosheet density distribution is precisely controlled by negative dielectrophoresis. Interestingly, the geometrical 2D shape of nanosheets plays an essential role in reducing optical light scattering in colloids and enhancing the dielectrophoretic controllability of nanosheet distribution. Moreover, despite the nematic assembly of 2D nanosheets in colloids, the birefringence effect is negligible, and polarization‐independent properties are obtained. Using a simple nanocolloidal cell with designed electrodes and various thicknesses, not only tunable lenses with either positive or negative focal lengths but also wide tunable lenses across positive and negative focal lengths are successfully demonstrated. Thus, the results reveal new possibilities for 2D nanocolloids in tunable GRIN optical applications.
Multiresponsive functional materials that respond to more than one external stimulus are promising for novel photonic, electronic, and biomedical applications. However, the design or synthesis of new multiresponsive materials is challenging. Here, this work reports a facile method to prepare a multiresponsive colloidal material by mixing a liquid‐crystalline 2D nanocolloid and a functional polymer colloid. For this purpose, electrically sensitive exfoliated α‐ZrP 2D nanocolloids and thermosensitive block copolymer colloids that are dispersed well in water are mixed. In the liquid‐crystalline nanocomposite, nematic, antinematic, or isotropic assemblies of α‐ZrP, nanoparticles can be electrically and selectively obtained by applying electric fields with different frequencies; furthermore, their rheology is thermally and reversibly controlled through thesol–gel–sol transition. The nanocomposite exhibits a solid gel phase within a predesigned gel temperature range and a liquid sol phase outside this range. These properties facilitate the design of a simple display device in which information can be electrically written and thermally stabilized or erased, and using the device, a battery‐free temperature maintenance indication function is demonstrated. The proposed polymer nanocomposite method can enrich the physical properties of 2D nanocolloidal liquid crystals and create new opportunities for eco‐friendly, reusable, battery‐free electro‐optical devices.
A flat lens with a tunable focal length that does not require mechanical movement is highly desirable in augmented reality (AR) or virtual reality (VR) systems, but its development poses significant challenges. A colloidal lens that uses dielectrophoretic (DEP) manipulation of nanoparticle density in a colloid can be a good solution for achieving tunability in flat lenses. In this study, we investigated the optical properties of a nanocolloidal lens containing two-dimensional (2D) α-zirconium phosphate (α-ZrP) nanoparticles and optimized the lens design parameters to achieve low image distortion and large focal length tunability. We simulated the nanoparticle distribution function as a function of applied voltage for various lenses with different electrode designs, and the simulation results matched well with experimental observations. Additionally, we identified a condition for lower power consumption. Finally, we identified specific design parameters that allow for wide focal length control without image deformation and utilized them to fabricate lenses for a simple AR system. This study clearly demonstrates the potential of tunable nanocolloidal lenses, particularly in AR systems, by optimizing their design and performance.
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