Electrically tunable birefringence of a polymer composite with long-range orientational ordering of liquid crystals

We report an optical film with electrically tunable birefringence in which the liquid crystals (LCs), mixed with the host polymer, form longrange ordering. The film was prepared through polymerization without phase separation between the LCs and polymers. Driving voltage below 30 V for full switching of birefringence is achieved in a 6 μm-thick film. Electro-optical investigations for the film suggest that the long-range ordering of the LCs mixed in the film caused by polymerization lead to rotations of the LCs as well as optical anisotropy in the film. These films with electrically tunable birefringence could have applications as flexible light modulators and phase retardation films for 2D-3D image switching. © 2014 Optical Society of America.1

Electroluminescent devices with function of electro-optic shutter

The polymer-dispersed liquid crystal (PDLC) was used as a dielectric layer of electroluminescent (EL) device to provide multi-function of electroluminescence and electro-optic shutter. A 50 μm-thick PDLC layer was formed between a transparent electrode and a ZnS:Cu phosphor layer. The electro-optic properties of the EL device were not distorted by the introduction of the PDLC layer. The extraction efficiency of luminescence was improved by more than 14% by PDLC layer. The transmittance of the PDLC was also founded not to be degraded significantly by excitation frequency. Therefore, the electroluminescence of the device was ignited by excitation frequency at a given voltage for full transparency of the PDLC. This device has great potential for applications in transparent displays with the function of a privacy window. © 2012 Optical Society of America.1

Luminance enhancement of electroluminescent devices using highly dielectric UV-curable polymer and oxide nanoparticle composite

A flexible hybrid structure electroluminescent (HSEL) device was fabricated from ZnS:Cu phosphor microparticles dispersed in a UVcurable polymer matrix. We observed a maximum luminance of 111 cd/m2 at 10 kHz and 170 V from a device wherein the mixing ratio between the phosphor particles and highly dielectric polymer binder was 70:30 wt%. Furthermore, by uniformly dispersing highly dielectric BaTiO3 nanoparticles within the polymer matrix, we were able to obtain a luminance of up to 211 cd/m2 in the HSEL device. Compared to the conventional thermal curing process, this UV process greatly simplifies the fabrication steps by combining phosphors and dielectric materials at room temperature. This process also demonstrates a promising pathway toward creating flexible and printed EL devices in the future. © 2014 Optical Society of America.1

Bidirectional two colored light emission from stress-activated ZnS-microparticles-embedded polydimethylsiloxane elastomer films

Bidirectional two-colored mechanoluminescent light emission has been demonstrated by unifying two polydimethylsiloxane elastomer layers functionalized with zinc sulfide doped with Cu (ZnS:Cu) or Cu and Mn (ZnS:Cu,Mn). The bilayered composite films are simply fabricated by dispensing uncured ZnS:Cu,Mn + PDMS onto previously spin-coated and ardened ZnS:Cu + PDMS film. The robust PDMS-PDMS bonding yields a ilm which can simultaneously emit light with color coordinates of (0.25, 0.56) and (0.50, 0.48), similar to the intrinsic colors of ZnS:Cu and ZnS:Cu,Mn, respectively. Composite films can emit light in upper and lower directions without fracture when it is stretched. © 2013 Optical Society of America.1

Microspinning: Local Surface Mixing via Rotation of Magnetic Microparticles for Efficient Small-Volume Bioassays

The need for high-throughput screening has led to the miniaturization of the reaction volume of the chamber in bioassays. As the reactor gets smaller, surface tension dominates the gravitational or inertial force, and mixing efficiency decreases in small-scale reactions. Because passive mixing by simple diffusion in tens of microliter-scale volumes takes a long time, active mixing is needed. Here, we report an efficient micromixing method using magnetically rotating microparticles with patterned magnetization induced by magnetic nanoparticle chains. Because the microparticles have magnetization patterning due to fabrication with magnetic nanoparticle chains, the microparticles can rotate along the external rotating magnetic field, causing micromixing. We validated the reaction efficiency by comparing this micromixing method with other mixing methods such as simple diffusion and the use of a rocking shaker at various working volumes. This method has the potential to be widely utilized in suspension assay technology as an efficient mixing strategy

Single metal path power transfer technology without return path at 13.56MHz ISM band

Using layers of mesh shaped and flat copper plate, this paper demonstrates single metal path power transfer system without return path through the surface of aluminum foil at 13.56MHz. Transceivers are isolated from the energy propagating medium but surface wave gets excited. This technology is free from co-alignment limitation between Tx and Rx, enabling free position of Rx with given metal plate environment. Around 20% power transfer efficiency was achieved with a LC matching network part

Mechanically driven light-generator with high durability

Mechanically activated luminescence from solids (mechanoluminescence) is a classical optical phenomenon induced in a substance when stressed or cleaved. However, no practical application has been realized due to its low luminescent intensity and lack of reproducibility. We demonstrate highly bright and durable mechanoluminescent flexible composite films with a brightness of ∼120 cd/m2 and durability over ∼100 000 repeated mechanical stresses by using a combination of copper-doped zinc sulfide (ZnS:Cu) particles and polydimethylsiloxane. Furthermore, the possibility of mechanoluminescent color-tuning by changing the repetitive stress rate on the composite films is also suggested. These findings can open a window for developing smart systems and opto-mechanical devices. © 2013 American Institute of Physics.

Simultaneous dual-channel blue/green emission from electro-mechanically powered elastomeric zinc sulphide composite

Mechanoluminescent (ML) materials, which luminesce in response to mechanical stimuli, are attractive candidates in developing energy-sustainable technology and are widely used in sensors, ubiquitous light sources, and displays. Metal-doped zinc sulphide (ZnS) is considered a promising ML material because it produces intense and lasting luminescence under repeated mechanical stresses. Previous studies of ZnS luminescence have focused on single-channel emission by electroluminescence (EL) or ML generated by applied electric fields or mechanical stresses, respectively. Here, we report the simultaneous generation of EL and ML from an elastomeric ZnS composite embedded with silver nanowires and demonstrate the independent control of both EL and ML responses. We describe the tuning of the strength and color of the EL/ML emissions from a single ZnS-based structure by applying combinations of electrical and mechanical excitation forces. We also demonstrate a multi-color-patterned EL/ML emitting display using the ZnS-based composite; this application may provide a basis for the development of new optomechanical displays. © 2016 Elsevier Ltd.

Textile-fiber-embedded multiluminescent devices: A new approach to soft display systems

In the recent remarkable advances in soft electronic systems, light-emitting functions play a prominent role. In particular, polymer composite systems with embedded luminescent particles have attracted considerable attention as a luminescent component owing to their flexibility and simple fabrication. However, most flexible composite-based electroluminescent (EL) devices have coplanar structures, requiring mechanically compliant electrodes with high transmittance, durability, and stable electrical conductivity. This is a limitation for systems designed for providing superior flexible characteristics without loss of luminescence. Here, we introduce a novel EL device architecture—a durable/flexible textile-fiber-embedded polydimethylsiloxane and zinc sulfide (PDMS + ZnS) composite, driven by an in-plane electric field, which eliminates the requirement for high transmittance. On applying an AC voltage, light is radially emitted from the ZnS particles surrounding the fibers, originating from the radially distributed electric/optical fields; the rolling and stretching flexibilities are maintained during this process. The device also exhibits strong EL intensities in a thick emitting layer—a parameter on which EL and mechanoluminescent (ML) intensities in coplanar structures are dependent. This is because the electric field is applied between in-plane fibers. Using this smart design, simultaneously high EL and ML intensities can be simply achieved by embedding fibers in strong ML-emitting PDMS + ZnS. We also present a patterned device controlled by different fiber embedding depths, utilizing the vertical and in-plane electric fields. This application may provide a basis for the development of emerging soft display systems that require high luminescence as well as flexibility in the light-emitting components. © 2019 Elsevier Ltd1