Smart Optical Devices Research Articles

Laser‐Direct‐Writing Reversible Aligned Wrinkling on Arbitrary Films Assisted by a Detachable Assembly Strategy

AbstractDynamic oriented wrinkling especially on arbitrary film materials is highly desirable yet remains a great challenge. Here, fabrication of programmable aligned wrinkling patterns on different film/substrate systems via a laser‐direct‐writing (LDW) method is reported, regardless of photofunctionality and transparence of the target films. The key is related to smart introduction of photothermal materials (PTMs) into compliant substrates and even as an independent attachable/detachable layer assembled underneath the film/substrate systems. Experiments and theoretical modeling reveal that with the help of the photothermal effect of PTMs, in situ LDW‐induced localized dynamic anisotropic stress field is responsible for the intriguing LDW path‐parallel aligned wrinkling. Furthermore, dimensional analysis is carried out and explicit solutions quantifying the connection of wrinkling morphology parameters with the LDW conditions are derived for the first time, which enables theoretical pattern designing. It is highlighted that the attachable/detachable assembly strategy for the independent PTMs layer endows arbitrary film/substrate systems with on‐demand photosensitivity when needed, which has been inaccessible previously. As demonstrated, these dynamic oriented wrinkling systems have found broad applications especially in smart soft photonics, e.g., information storage, anticounterfeiting, and responsive optical devices.

Unprecedented Silver‐Based Hybrid Pyroelectric Enabling Wide Spectral Photo‐Pyroelectricity for Birefringence Photomodulation

AbstractBirefringent crystal, which has the capacity to manipulate polarization light, holds an indispensable position in optics and optoelectronics, while it remains challenging to fulfill the modulation of birefringence. Here, we present wide spectral photo‐pyroelectric effect in a silver‐based hybrid pyroelectric, (N‐CHM)Ag2I3 (N‐CHM=N‐cyclohexylmethylamine), serving as a feasible strategy to regulate birefringence through light stimuli. As the first silver‐based hybrid pyroelectric, (N‐CHM)Ag2I3 exhibits strong room‐temperature photo‐pyroelectricity with a large polarization of ~3.23 μC/cm2 and high voltage responsivity of ~0.96 m2/C across the UV–NIR spectral region. Strikingly, the photomodulation of its in‐plane birefringence is established through pyroelectric effect, giving a saturation value of ~1.68×10−2 that is among the highest level achieved to date. This study on the birefringence photomodulation of lead‐free hybrid pyroelectric is anticipated to boost future development of new smart optical and optoelectronic devices.

Unprecedented Silver-Based Hybrid Pyroelectric Enabling Wide Spectral Photo-Pyroelectricity for Birefringence Photomodulation.

Birefringent crystal, which has the capacity to manipulate polarization light, holds an indispensable position in optics and optoelectronics, while it remains challenging to fulfill the modulation of birefringence. Here, we present wide spectral photo-pyroelectric effect in a silver-based hybrid pyroelectric, (N-CHM)Ag2I3 (N-CHM=N-cyclohexylmethylamine), serving as a feasible strategy to regulate birefringence through light stimuli. As the first silver-based hybrid pyroelectric, (N-CHM)Ag2I3 exhibits strong room-temperature photo-pyroelectricity with a large polarization of ~3.23 μC/cm2 and high voltage responsivity of ~0.96 m2/C across the UV-NIR spectral region. Strikingly, the photomodulation of its in-plane birefringence is established through pyroelectric effect, giving a saturation value of ~1.68×10-2 that is among the highest level achieved to date. This study on the birefringence photomodulation of lead-free hybrid pyroelectric is anticipated to boost future development of new smart optical and optoelectronic devices.

A Tunable Hydrophilic-Hydrophobic, Stimulus Responsive, and Robust Iridescent Structural Color Bionic Film with Chiral Photonic Crystal Nanointerface.

Bio-inspired in nature, using nanomaterials to fabricate the vivid bionic structural color and intelligent stimulus responsive interface as smart skin or optical devices are widely concerned and remain a huge challenge. Here, the bionic flexible film is designed and fabricated with chiral nanointerface and tunable hydrophilic-hydrophobic by the ultrasonic energy perturbation strategy and crosslinking of the cellulose nanocrystals (CNC). An intelligent nanointerface with adjustable hydrophilic and hydrophobic properties is constructed by the supramolecular assembly using a smart ionic liquid molecule. The bionic flexible film possessed the variable hydrophilic-hydrophobic, stimulus responsive, and robust iridescent structural color. The reflective wavelength and the helical pitch of the film can be easily modulated through the ultrasonic energy perturbation strategy. The bionic flexible film by covalent cross-linking has excellent robustness, good elasticity and flexibility. The tunable brilliant structural color of the chiral nanointerface is attributed to the surface charge change of the CNC photonic crystal, which is disturbed by ultrasonic energy perturbation. The bionic flexible film with tunable structure color has intelligent hydrophilic and hydrophobic stimulus response properties. The chiral bionic materials have potential applications in smart skin, optical devices, bionic materials, robots, anti-counterfeiting, colorful displays, and stealth materials.

The role of smart optical biosensors and devices on predictive analytics for the future of aquaculture systems

Recirculating aquaculture systems (RAS) have been rising quickly in the last decade, representing a new way to farm fish with sustainable aquaculture practices. This system is an environmentally and economically sustainable technology for farming aquatic organisms by reusing the water in production. RAS present some benefits compared with other aquaculture methods, for instance, allows the minimization of water usage and disease occurrence, the absence of antibiotics in these systems, shortens the production cycle, functions as a water treatment system, allows the improvement of the feed conversion, and a reduction in the alteration of coastal habitat, among others. However, this is a complex system with complex interactions between the number of fish and water quality parameters, which can compromise the fish welfare. Currently, there is a huge gap in the global aquaculture sector in terms of smart sensors for cortisol (stress hormone), bacteria, water pollutants, volatile organic compounds and micro/nano-plastics assessment. This sector does not measure such critical parameters which brings a weak understanding of the wellbeing of fish. Therefore, it is crucial to implement point of care (POC) sensors for those critical parameters’ assessment via multiparameter solution and predictive analytic capabilities for data supply. This work presents an overall introduction about the impact of the RAS on fish production and its necessity as protein as well as the actual solutions for those problems. Additionally, it reviews the actual state of the art in terms of potential multiparameter POC sensors and predictive analytical approaches that have been investigated in recent years for future application in aquaculture with the aim to guide the researchers on the sector’s needs. Additionally, future perspectives are also described in order to digitize the aquaculture sector with novel optical systems and biosensing elements.

Low-voltage electrochromic behaviour of polymer-stabilised liquid crystal with considerable broadband reflection

ABSTRACT In this work, a novel method was proposed to achieve electric-induced colouration of polymer-stabilised liquid crystal (PSLC) with considerable broadband reflection. The formation of broadband reflection was due to the introduction of the UV absorber that induced a light intensity gradient within the liquid crystal system and promoted the non-uniform distribution of the pitch. Experiments were performed to optimise the components and polymerisation conditions, allowing the bandwidth to be broadened from 252 nm to 906 nm. The texture of PSLC was characterised using POM, revealing that the planar texture was not disrupted. Thereafter, the addition of ionic liquid as supporting electrolyte enabled the PSLC to be switched from colourless to coloured at DC voltage as low as 1.7 V and the colouration behaviour can be independently modulated by changing the voltage level and the duration. Meaningfully, after the DC electric field was removed, the colour of the PSLC can also disappear gradually. In addition, the as-prepared electrochromic PSLC presented enhanced UV shielding, IR thermal control efficacy and good colouration performance on flexible substrates, which can be applied to low-energy smart glass and thermal management of buildings. This study provided a promising approach for the development of smart optical devices.

Versatile Photoluminescence Polymers for Printed Transparent Self‐Healing Optical Devices

AbstractThe development of comprehensive optical self‐healing polyurethane polymers for smart optical devices presents a significant challenge due to the trade‐off between intrinsic self‐healing capability and mechanical strength. This study focuses on the synthesis of versatile photoluminescence supramolecular polymers that integrate self‐healing ability, mechanical strength, and fluorescence responsiveness. The incorporation of hydrogen bonds and disulfide bonds into the dynamic hard domain results in the optimal polymer exhibiting impressive mechanical properties (strength, 27.0 MPa; toughness, 132.1 MJ m−3; elongation at break, 1450%), as well as a conspicuous self‐healing efficiency (surface scratches disappear within just 1 min). Furthermore, the transparent (transparency >97%) and colorless polymers demonstrate aggregation‐induced emission, characterized by intense cyan fluorescence that transitions to subdued blue fluorescence upon stretching under 365 nm irradiation. Proof‐of‐concept experiments demonstrate that screen‐printed fluorescent patterns, based on as‐prepared fluorescence ink associated with dual‐mode upconversion emission, are able to successfully encode fluorescence information, and can be integrated into the self‐healable 3D optical devices. The self‐healing optical devices designed with versatile polymers and featuring diversified patterns offer a promising direction for the advancement and application of future self‐healing materials.

Rapid and low-temperature preparation of tungsten oxide electrochromic thin films by oxygen plasma treatment

Electrochromic materials have attracted considerable attention due to their ability to change color reversibly and rapidly under an external electrical stimulus, making them highly promising for use in various applications such as smart windows, displays, and optical memory devices. In particular, tungsten trioxide (WO3) thin films have shown excellent electrochromic properties, leading to their wide application in electrochromic devices. In this study, oxygen plasma treatment was used to convert WCl6 thin film to WO3 electrochromic thin film on ITO glass substrate. Surface morphology, element composition, phase, optical property, and electrochromic characteristics of WO3 film are analyzed. It has been proved that the conversion of precursor films is rapid and efficient, the mean roughness and root mean square of amorphous WO3 thin film are lower than 1.8 nm and 2.2 nm respectively, and the film exhibits good electrochromic performance parameters. The optical modulation range and coloration efficiency of the film can reach 58.5% and 80.2 cm2/C before cycle and 56.3% and 84.0 cm2/C after 100 cycles, coloration time and bleaching time are within 10 s. The method of plasma treatment avoids annealing and prepare WO3 film with good and stable performance. This method has the potential to expand to other electrochromic materials, and provides a new solution for the large area preparation and flexible application of electrochromic materials.

Fabrication of mesogenic epoxy microsphere-filled negative-dielectric-anisotropy cholesteric liquid crystals for bistable devices

Bistable devices, which can operate in two field-free stable states, are highly desirable for developing smart optical devices with true energy conservation. Cholesteric liquid crystals (CLCs) have been demonstrated as promising candidates for fabricating smart windows and light modulators with bistable characteristics. However, not all CLCs can be fabricated into bistable devices. It is meaningful to develop new technologies to process the CLCs that only have one stable field-free state into bistable devices. In this work, mesogenic epoxy microspheres are prepared by thermal curing between a liquid crystalline epoxide and a thiol monomer in a negative-dielectric-anisotropy CLC solvent to obtain mesogenic epoxy microsphere-filled CLCs. The mesogenic epoxy microspheres are expected to provide anchoring energy to increase the energy barrier between focal-conic and planar textures. The pristine CLC host is only stable in the planar texture, and its focal-conic texture and low-transmittance state cannot be maintained for a long time in the absence of electric fields with a low frequency. On the contrary, for mesogenic epoxy microsphere-filled CLCs, both the planar texture/large-transmittance state and the focal-conic texture/low-transmittance state of the cholesteric phase can be stable for a long time without continuous power input. Moreover, the mesogenic epoxy microsphere-filled CLCs is also developed into bistable smart windows with low energy consumption. This work could provide a simple and interesting strategy for fabricating the bistable CLC devices promising for applications in energy-saving fields.

Quantifying the hybrid flow and aperture forming of liquid metals immersed in NaOH solution under rotating magnetic field

AbstractLiquid metal (LM) immersed in solutions exhibited profound fluidic phenomena under various working situations. With persistent research endeavor, a growing number of intriguing phenomena along this direction have been increasingly disclosed. Among the many critical issues, quantifying the hybrid flow of LMs and surrounding solutions often encounters tough challenges due to the large property differences between the two fluids, including density, electrical and fluidic characteristics, and so forth. Especially, when the electromagnetic field is involved, the problems would become ever complicated. In this article, to characterize the hybrid fluids of LM and NaOH solution under rotating magnetic field (RMF), we established a coupled three‐dimensional model considering magnetic effect on the two‐phase flow. The computational prediction of the model was validated through comparing the simulated morphological features of LM with the experimental measurements at different rotational speeds of magnetic field. Finally, two phenomena were revealed with potential applications interpreted: (1) LM would accelerate the solution due to their difference in viscosity; (2) an asymmetric flow and tunable hole formation under RMF will occur due to the surface tension redistribution on LM. The present works are expected to provide reliable guidance for quantifying the multiphase flow behaviors of hybrid fluids composed of LM and other liquids. The revealed hole size dominated LM aperture is especially useful for developing future smart optical switch and electromagnetic shielding devices.

Flexible Crystal Heterojunctions of Low-Dimensional Organic Metal Halides Enabling Color-Tunable Space-Resolved Optical Waveguides.

Molecular luminescent materials with optical waveguide have wide application prospects in light-emitting diodes, sensors, and logic gates. However, the majority of traditional optical waveguide systems are based on brittle molecular crystals, which limited the fabrication, transportation, storage, and adaptation of flexible devices under diverse application situations. To date, the design and synthesis of photofunctional materials with high flexibility, novel optical waveguide, and multi-port color-tunable emission in the same solid-state system remain an open challenge. Here, we have constructed new types of zero-dimensional organic metal halides (Au-4-dimethylaminopyridine [DMAP] and In-DMAP) with a rarely high elasticity and rather low loss coefficients for optical waveguide. Theoretical calculations on the intermolecular interactions showed that the high elasticity of 2 molecular crystalline materials was original from their herringbone structure and slip plane. Based on one-dimensional flexible microrods of 2 crystals and the 2-dimensional microplate of the Mn-DMAP, heterojunctions with multi-color and space-resolved optical waveguides have been fabricated. The formation mechanism of heterojunctions is based on the surface selective growth on account of the low lattice mismatch ratio between contacting crystal planes. Therefore, this work describes the first attempt to the design of metal-halide-based crystal heterojunctions with high flexibility and optical waveguide, expanding the prospects of traditional luminescent materials for smart optical devices, such as logic gates and multiplexers.

Dynamic metal patterns of wrinkles based on photosensitive layers

Regulating metal surfaces with micro-/nanoscale structures is of great significance for both material science and potential applications. However, the intrinsic properties of metals, such as fixed isotropic moduli and inflexible structures, in a sense present major limitations in developing next-generation smart patterned surfaces. In this work, a facile and general patterning strategy is proposed to endow insensitive metal surfaces with controllable spontaneous topologies and dynamic performance by exquisitely introducing an essential photosensitive interlayer. The arresting anthracene-containing photocrosslinking interlayer can selectively predetermine the anisotropic property of compliant bilayers without damaging metals’ homogeneous properties, and realize a changeable stiff/soft layer. Furthermore, the mechanical transition mechanism of the self-adaptive wrinkling modes in metal-based trilayer systems is revealed to pave the pathway for regulating functional wrinkled metal surfaces. This photodriven metal patterning strategy can promote the development of brand-new methods for tuning the instability of multilayered materials, and be potentially applied in smart optical devices with dynamic reflectance, including light gratings and “magic” mirrors.

Transparent and Self-Healing Elastomers for Reconfigurable 3D Materials.

Transparent soft materials are widely used in applications ranging from packaging to flexible displays, wearable devices, and optical lenses. Nevertheless, soft materials are susceptible to mechanical damage, leading to functional failure and premature disposal. Herein, a transparent self-healing elastomer that is able to repair the polymer network via exchange reactions of dynamic disulfide bonds is introduced. Due to its self-healing ability, the mechanical properties of the elastomer can be recovered as well as its transparency after multiple cycles of abrasion and healing. The self-healing polymer is fabricated into 3D structures by folding or modular origami assembly of planar self-healing polymer sheets. The 3D polymer objects are employed as storage containers of solid and liquid substances, reactors for photopolymerization, and cuvettes for optical measurements (exhibiting superior properties to those of commercial cuvettes). These dynamic polymers show outstanding mechanical, optical, and recycling properties that could potentially be further adapted in adaptive smart packaging, reconfigurable materials, optical devices, and recycling of elastomers.

Tunable antireflective characteristics enabled by small yellow leafhopper-inspired soccer ball-shaped structure arrays

BackgroundNowadays, tunable antireflective characteristics have attracted considerable attention due to growing demands in next-generation optical energy-related fields. MethodBioinspired by the distinctive structural geometry on small yellow leafhopper wings, this study reports reversibly switchable antireflective characteristics enabled by ambient-temperature shape memory polymer-based soccer ball-shaped structure arrays with multilayer porous structures underneath. Significant findsThe resulting structures behave a broadband omnidirectional antireflection performance, where the average reflectance in the visible spectrum can even be reduced by 22% for an incident angle of 75º. Interestingly, the structures can be instantaneously deformed or recovered through applying external stimuli in ambient environments. The antireflective property switches associated with the shape memory transitions deliver vast opportunities in developing smart optical devices. Moreover, the structure-shape effect and reversibility on the antireflective properties are systematically assessed in the research.

Dynamic Refractive Index-Matching for Adaptive Thermoresponsive Smart Windows.

Thermoresponsive smart windows (TRSWs) take great advantages in energy-efficient buildings and on-demand devices owing to their self-adaptiveness and external energy consumption-free nature. Currently used TRSWs largely rely on thermal-induced phase transitions in single-material systems, however, the intrinsic characteristics of which may not be suited for practical window utilization, such as poor luminous transparency and fixed critical temperature (Tc ). Herein, an adaptive TRSW based on dynamic refractive index (RI) matching between two phases is demonstrated, which is facilely fabricated by embedding ethylene glycol solution microdroplets into polydimethylsiloxane (PDMS) via a one-step emulsification approach, realizing a smart temperature response in PDMS. The TRSW presents high transparency (≈92%) and bidirectional transparency-temperature response (≈20% at 73°C, ≈40% at 8°C). Moreover, the RI dispersion generates a unique effect of wavelength selectivity with temperature. Notably, the effective optical-temperature response with variable Tc could be tuned over a wide range of 13-68°C by adjusting the EGS concentration. The proposed strategy with dynamic RI matching allows TRSW construction to extend beyond phase transitional materials and greatly broadens the applicable scope of TRSWs, which is promising in the fields of smart optical devices such as smart windows, anti-counterfeiting, optical switches, and optical selection.

Integrated electrochromic and electrofluorochromic properties from polyaniline-like polymers with triphenylacrylonitrile as side groups

Recent years have witnessed rapid developments in electrochromic/ electrofluorochromic (EC/EFC) materials. Though highly efficient ECs have been realized in a lot of systems, the synchronous EFC performance is still severely limited by the low luminescent efficiency (Φf) and slow response. In this work, we designed and synthesized conjugated polymers PDTEC and PTEC, which are composed of polyaniline-like main chains and triphenylacrylonitrile (TPAN) side chains. Both polymers exhibit remarkable color changes between yellow, orange and blue, and fluorescent on/off switchings upon applied potentials. Notably, especially high Φf (44.2%), fluorescent contrast (Ion/off=4339) and fast response (0.18s) are simultaneously accomplished, which is rarely found in EFC materials due to the difficulty in balancing both electrochemical activity and luminescent capacity in polymers. Such fascinating comprehensive EC/EFC performance will render these polymers promising candidates for versatile applications in smart optical devices and biosensors.

Dynamic Surface Wrinkles for In Situ Light-Driven Dynamic Gratings.

Dynamic diffraction gratings (DDGs) are considered as one of the most promising technologies for application in smart optical devices because of their in situ dynamic regulation of light propagation on demand; however, it is still a challenge to fabricate dynamic periodic micro/nanostructures due to limited materials and processes. Here, a facile and feasible strategy to construct a near-infrared (NIR) radiation-driven DDG is developed based on a double-sided surface pattern, which is fabricated by dynamic wrinkles and/or soft-imprinted static wrinkles. Poly(dimethylsiloxane) (PDMS) containing carbon nanotubes (CNTs) serves as the substrate, and wrinkles are formed on both sides. The resulting double-sided wrinkle pattern can be used as a DDG to generate various adjustable two-dimensional (2D) diffraction patterns driven by NIR light. Furthermore, with various combinations of wrinkles, we demonstrated a single-sided responsive DDG and a double-sided responsive DDG to realize the evolution of diffraction patterns from 2D to one-dimensional (1D) and 2D to zero-dimensional (0D), respectively. The results provide an alternative for DDGs that will have wide applications in smart display, sensing, and imaging systems.

Strain and illumination triggered regulations of up-conversion luminescence in Er-doped Bi0.5Na0.5TiO3[sbnd]BaTiO3/Mica flexible multifunctional thin films

External stimuli induced effective regulations of luminescent material are of significant interest in the development of smart optical devices. Here, by simply doping with Er3+ in the 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 (BNTBT) ferroelectric host, using the bendable mica substrate, and exerting mechanical strain (bending) or light illumination (via photochromic reaction), the all-inorganic, highly-transparent and flexible Er-doped BNTBT/Mica luminescent-ferroelectric thin films were designed and fabricated, displaying strain-induced dramatically elevation of up-conversion photoluminescence (PL) intensity, suppression of PL concentration quenching, outstanding endurance and durability, convenient illumination-mediated PL quenching. And the strain-induced structural changes and local lattice distortions of the thin films were further explored through theoretical calculations and Raman measurement. Our results can supply the guidance of designing other luminescent-ferroelectric materials with controlled PL properties via easy mechanical/photo stimuli for expanding the application of multifunctional wearable memory devices.

Asymmetric chiral disazo dopants with high anisotropy for versatile modulation of liquid crystal optics

As key elements, anisotropic chiral dopants determine the helical twisting power (HTP) of doped cholesteric liquid crystal (CLC) system by the host–guest interaction. To reveal the intrinsic structure–function relationship, we developed 3 novel asymmetric and photo-responsive chiral derivatives bearing axial chiral binaphthol moiety and disazo chromophore. They exhibited reversible photoisomerization, and rapidly induced helical degeneration of the doped CLC mixture under UV irradiation. Furthermore, highly asymmetric (R)-2′-hydroxy-[1,1′-binaphthalen]-2-yl 3,5-bis((E)-(4-butoxyphenyl)diazenyl)benzoate (molar absorption coefficient: 28,090 L⋅mol−1⋅cm−1; half-life period: 10.28 h; HTP: −34 um−1 in E7) was adopted to construct the CLC film with excellent NIR-reflection adjusted by light, heat, and electric field. It is a promising photoswitch agent for application in advanced smart materials and optical devices.

Highly transparent RCF/PTFE humidity and IR light dual-driven actuator with high force density, sensitivity and stability

Transparent actuators have received great interest among researchers due to their potential applications in tactical displays, optical switches, zoom lenses, etc. In this work, we designed and developed a highly transparent cellulose-based actuator, made of regenerated cellulose film (RCF) and hydrophobic polytetrafluoroethylene (PTFE) two-layered film, which was fabricated by using a simple sputtering method to grow PTFE film on the RCF film. The RCF/PTFE actuator exhibits high sensitivity towards both humidity- and IR light-driving responses, which can be attributed to thermal expansion and hygroscopic expansion differences between RCF film and PTFE film. The stability of the actuator was greatly improved by O plasma etching of the RCF film surface. Bi-directional actuation of the actuator can be achieved by controlling the ambient humidity and IR light irradiation, with the bending angle changing from 0° to 360° within 14 s and 10 s, respectively. Numerical simulations show that the sensitivity and stress of RCF/PTFE actuators are more than one order of magnitude higher than petroleum-based actuators, which can be attributed to the unique hygroscopic effect of cellulose. The as-obtained actuator may have potential applications in the fields of smart window, bionic robot, optical devices, sensing and camouflage.