Macroporous Photonic Crystals Research Articles

Tuning Spatially Resolved Shape Memory Effects of Stimuli‐Responsive Macroporous Photonic Crystals

Stimuli‐responsive photonic crystals with patterned microstructures are of great interest in developing reconfigurable nanooptical devices. Leveraging unconventional all‐room‐temperature shape memory efforts and spatially resolved photopolymerization, here we report a facile method for micropatterning stimuli‐responsive photonic crystals. Macroporous shape memory polymer (SMP) photonic crystals fabricated by colloidal templating can be deformed by cold programming, triggering the disappearance of their original structural colors. Exposure of the deformed samples to UV light through a photomask selectively disables the shape memory capabilities in the UV‐exposed regions. Hidden micropatterns defined by the photomask can be revealed by exposing the colorless SMP films to ethanol vapor, which triggers the shape memory recovery of the “memorized” ordered microstructures and the corresponding structural colors. Extensive nanoindentation experiments indicate that the exposure to UV light increases the crosslinking density and enhances the elastic modulus and toughness of the exposed regions by a factor of ∽2.0 and ∽5.2, respectively. Due to the formation of these extra crosslinks in the deformed configuration, they prevent normal shape memory behavior where the strained polymer chains rearrange from the temporary to permanent configuration when triggered by an external stimulus. This simple micropatterning technology can enable multi‐stimuli‐responsive reconfigurable nanophotonic devices and chromogenic anticounterfeiting labels.This article is protected by copyright. All rights reserved.

Clairvoyant Melon Maturity Detection Enabled by Doctor-Blade-Coated Photonic Crystals.

Climacteric fruits are harvested before they are ripened to avoid adverse damages during transport. The unripe fruits can undergo ripening processes associated with rind color changes on exposure to ethanol vapors. Although rind coloration is a common indicator showing fruit maturity, the attribute does not provide reliable assessment of maturity especially for melons. Herein, we report the achievement of sensitive and reversible melon maturity detection using macroporous hydrogel photonic crystals self-assembled by a roll-to-roll compatible doctor-blade-coating technology. The consumption of applied ethanol vapor during melon ripening results in less condensation of ethanol vapor in the pores (250 nm in diameter), leading to a distinct blue-shift of the optical stop band from 572 to 501 nm and an obvious visual colorimetric readout from yellow green to blue. Moreover, the dependence of the color change on Brix value within the melon has also been evaluated in the study.

Macroporous Superhydrophobic Coatings with Switchable Wettability Enabled by Smart Shape Memory Polymers

AbstractHere, a facile bottom‐up nanofabrication technology for making smart superhydrophobic coatings with switchable wettability and tunable optical properties by integrating shape memory polymers (SMPs) with templated macroporous photonic crystals is reported. Thermoresponsive shape memory efforts exhibited by a polyurethane‐based shape memory copolymer enable reversible microstructural transitions between a “memorized” permanent configuration composing of highly ordered arrays of macropores and a temporary deformed structure with collapsed macropores. The unique macroporous SMP photonic crystal arrays with large surface roughness can entrap a large portion of air in the interconnecting macropores, resulting in superior superhydrophobic properties including high apparent water contact angle (CA > 160°) and low CA hysteresis. Importantly, the shape memory‐enabled microstructural transitions lead to drastic wettability switching from superhydrophobic (CA > 160°) to hydrophobic (CA ≈ 110°) or from oleophobic (CA ≈139° for hexadecane) to oleophilic (CA ≈ 80°). The large CA tunability (>50°) coupled with the simultaneous color change from shining iridescence to colorless associated with the same microstructural transition can not only provide a noninvasive means for visually indicating the surface wetting states, this favorable coupling between the wetting and optical behaviors of macroporous SMP photonic crystal membranes can also pave the way for developing new tunable nanooptical devices.

Water-Soluble Chemical Vapor Detection Enabled by Doctor-Blade-Coated Macroporous Photonic Crystals

Water-soluble chemicals, involving a wide range of toxic chemicals in aqueous solutions, remain essential in both daily living or industrial uses. However, most toxicants are evaporated with water through their use and thus cause deleterious effects on the domestic environment and health in humans. Unfortunately, most current low-dose chemical vapor detection technologies are restricted by the use of sophisticated instruments and unable to promptly detect the quantity of diverse toxicants in a single analysis. To address these issues, this study reports the development of simple and fast chemical vapor detection using doctor-blade-coated macroporous poly(2-hydroxyethyl methacrylate)/poly(ethoxylated trimethylolpropane triacrylate) photonic crystals, in which the poly(2-hydroxyethyl methacrylate) has strong affinity to insecticide vapor owing to a favorable Gibbs free energy change for their mixing. The condensation of water-soluble chemical vapor therefore results in a significant reflection peak shift and an obvious color change. The visual colorimetric readout can be further improved by increasing the lattice spacing of the macroporous photonic crystals. Furthermore, the dependence of the reflection peak position on vapor pressure under actual conditions and the reproducibility of vapor detecting are also evaluated in this study.

How Light Passes Through Ordered Macroporous Photonic Crystals Immersed in Solvents

Understanding light transmission through 3D macroporous photonic crystals is essential for linking their optical characteristics to any application, particularly when immersed in solvents. We examined TiO2 and SnO2 IOs in a series of common solvents to fix existing issues in Bragg-Snell theory and the definition of the photonic crystal unit cell and pore infilling. Using a comprehensive angle-resolved light transmission study coupled to microscopy examination of the IO structure, we demonstrate experimentally and theoretically that low fill factors are caused by porous material infilling all interstitial vacancies of the colloidal opal template, instead of complete filling of most interstitial voids. By also including an optical interference condition for inverse opals with a larger effective refractive index than their substrate, the optical data for macroporous photonic crystals are now consistent with microscopy measurements. This analysis provides an accurate correlation between the true response of a macroporous photonic crystal to tits primary properties including the index contrast with a solvent, infilled structure and the unit cell definition, and the directionality of the photonic band gap. As control in functional porous and ordered photonic materials has broadening to include biosensing and energy storage for example, a comprehensive and consistent description of how light passes through ordered macroporous photonic crystal structures is an important requirement.

Three-dimensional macroporous photonic crystal enhanced photon collection for quantum dot-based luminescent solar concentrator

A luminescent solar concentrator (LSC) is a photon managing device that can harvest, direct and concentrate solar light to small areas, enabling subsequent coupling to photovoltaic devices (PVs) for enhanced solar energy conversion. However, the intrinsic photon loss through the so-called escape cone of the LSCs significantly limits their light harvesting and concentrating performance. In this work, we introduce a facile and low-cost approach for the fabrication of a three-dimensional (3D) macroporous photonic crystal (PC) filter as an efficient photon reflector, which can be coated onto quantum dot (QD) based LSC devices. We demonstrate that by controlling the PC reflection band to match the emission profile of the QD emitters, the light trapping efficiency of the PC coated LSC (PC-LSC) can be significantly improved from 73.3% to 95.1% as compared to the conventional PC-free LSC due to the reduced escape cone photon loss. In addition, we have developed a simulation model that considers the PC reflector effect. Both experimental and simulation results show that the enhancement in LSC device performance induced by the PC reflector increases with increasing dimension. In fact, simulation data predicts a maximum of 13.3-fold enhancement in external quantum efficiency (EQE) and concentration factor (C factor) of the PC-LSC under more ideal conditions. Moreover, the simulation result offers insight into the relationship between photon output efficiencies and the geometric design of the PC-LSC. Our study sheds light on future design and fabrication of LSC devices with enhanced photon collection and concentrating efficiencies through novel and wavelength-selective photon reflectors.

Programmable Macroporous Photonic Crystals Enabled by Swelling‐Induced All‐Room‐Temperature Shape Memory Effects

AbstractThis study reports unconventional, all‐room‐temperature shape memory (SM) effects using templated macroporous shape memory polymer (SMP) photonic crystals comprising a glassy copolymer with high‐glass transition temperature. “Cold” programming of permanent periodic structures into temporary disordered configurations can be achieved by slowly evaporating various swelling solvents (e.g., ethanol) imbibed in the interconnecting macropores. The deformed macropores can be instantaneously recovered to the permanent geometry by exposing it to vapors and liquids of swelling solvents. By contrast, nonswelling solvents (e.g., hexane) cannot trigger “cold” programming and SM recovery. Extensive experimental and theoretical investigations reveal that the dynamics of swelling‐induced plasticizing effects caused by fast diffusion of solvent molecules into the walls of macropores with nanoscopic thickness dominate both “cold” programming and recovery processes. Importantly, the striking color changes associated with the reversible SM transitions enable novel chromogenic sensors for selectively detecting trace amounts of swelling analytes mixed in nonswelling solvents. Using ethanol–hexane solutions as proof‐of‐concept mixtures, the ethanol detection limit of 150 ppm has been demonstrated. Besides reusable sensors, which can find important applications in environmental monitoring and petroleum process/product control, the programmable SMP photonic crystals possessing high mechanical strengths and all‐room‐temperature processability can provide vast opportunities in developing reconfigurable/rewritable nanooptical devices.

Self-Assembled Curved Macroporous Photonic Crystal-Based Surfactant Detectors.

Surfactants are extensively used as detergents, dispersants, and emulsifiers. Thus, wastewater containing high-concentration surfactants discharged to the environment pose a serious threat to the ecosystem. Unfortunately, conventional detection methods for surfactants suffer from the use of sophisticated instruments and cannot perform detections for various surfactants by a single analysis. The article reports the development of simple and sensitive surfactant detection using doctor-blade-coated three-dimensional curved macroporous photonic crystals on a cylindrical rod. The photonic crystals exhibit different hydrophobicities at various angular positions after surface modification. The penetration of aqueous surfactant solutions in the interconnected macropores causes red-shift as well as reduction in amplitude in the optical stop bands, resulting in surfactant detection with visible readout. The correlation between the surface tension, as well as the solution-infiltrated angular position, and the concentration of aqueous surfactant solutions has also been investigated in this study.

Visual and reversible carbon dioxide sensing enabled by doctor blade coated macroporous photonic crystals

With significant impacts of carbon dioxide on global climate change, carbon dioxide sensing is of great importance. However, most of the existing sensing technologies are prone to interferences from carbon monoxide, or suffer from the use of sophisticated instruments. This research reports the development of reproducible carbon dioxide sensor using roll-to-roll compatible doctor blade coated three-dimensional macroporous photonic crystals. The pores are functionalized with amine groups to allow the reaction with carbon dioxide in the presence of humidity. The adsorption of carbon dioxide leads to red-shift and amplitude reduction of the optical stop bands, resulting in carbon dioxide detection with visible readout. The dependences of the diffraction wavelength on carbon dioxide partial pressure for various amine-functionalized photonic crystals and different humidities in the environment are systematically investigated. In addition, the reproducibility of carbon dioxide sensing has also been demonstrated in this research.

Reconfigurable Photonic Crystals Enabled by Multistimuli-Responsive Shape Memory Polymers Possessing Room Temperature Shape Processability.

Traditional shape memory polymers (SMPs) are mostly thermoresponsive, and their applications in nano-optics are hindered by heat-demanding programming and recovery processes. By integrating a polyurethane-based shape memory copolymer with templating nanofabrication, reconfigurable/rewritable macroporous photonic crystals have been demonstrated. This SMP coupled with the unique macroporous structure enables unusual all-room-temperature shape memory cycles. "Cold" programming involving microscopic order-disorder transitions of the templated macropores is achieved by mechanically deforming the macroporous SMP membranes. The rapid recovery of the permanent, highly ordered photonic crystal structure from the temporary, disordered configuration can be triggered by multiple stimuli including a large variety of vapors and solvents, heat, and microwave radiation. Importantly, the striking chromogenic effects associated with these athermal and thermal processes render a sensitive and noninvasive optical methodology for quantitatively characterizing the intriguing nanoscopic shape memory effects. Some critical parameters/mechanisms that could significantly affect the final performance of SMP-based reconfigurable photonic crystals including strain recovery ratio, dynamics and reversibility of shape recovery, as well as capillary condensation of vapors in macropores, which play a crucial role in vapor-triggered recovery, can be evaluated using this new optical technology.

Reusable macroporous photonic crystal-based ethanol vapor detectors by doctor blade coating

This research reports the development of sensitive and reversible vapor detection by using three-dimensional macroporous photonic crystals. A scalable and roll-to-roll compatible doctor blade coating technology is utilized to fabricate flexible macroporous poly(ethoxylated trimethylolpropane triacrylate) (PETPTA) films with hexagonal close-packed pores which are interconnected. The pores are then coated with a layer of poly(2-hydroxyethyl methacrylate) (PHEMA) to create macroporous PHEMA/PETPTA films. The condensation of vapors in the PHEMA coated macroporous films leads to the increase of both the PHEMA swelling degree and the effective refractive index of the diffractive medium, resulting in the red-shift and amplitude reduction of the optical stop bands. The optical measurements reveal that the diffraction from the as-prepared macroporous photonic crystals sensitively monitors the vapor pressure of ethanol since the PHEMA layer displays a great volume dependence on ethanol due to a decreased Flory-Huggins mixing parameter. The dependence of the diffraction wavelength on vapor pressure and the reproducibility of vapor sensing have also been investigated in this study.

Macroporous photonic crystal-based anti-ultraviolet and anti-near-infrared materials by doctor blade coating

In this article, we report a roll-to-roll compatible bottom-up self-assembly approach to fabricate double-multilayer macroporous polymer photonic crystals consisting of a multilayer of three-dimensional (3D) hexagonal close-packed (HCP) 200 nm spherical pores and a multilayer of 3D HCP 500 nm spherical pores. Both optical measurements and theoretical predictions reveal that the as-prepared polymer film exhibits anti-ultraviolet and anti-near-infrared properties caused by the Bragg's diffractive of incident ultraviolet radiation and near-infrared radiation from the crystalline lattice of air cavities in the polymer film.

Photonic Crystals: Optically Bistable Macroporous Photonic Crystals Enabled by Thermoresponsive Shape Memory Polymers (Advanced Optical Materials 11/2015)

Photonic Crystals: Optically Bistable Macroporous Photonic Crystals Enabled by Thermoresponsive Shape Memory Polymers (Advanced Optical Materials 11/2015)

Direct Writing of Three-Dimensional Macroporous Photonic Crystals on Pressure-Responsive Shape Memory Polymers.

Here we report a single-step direct writing technology for making three-dimensional (3D) macroporous photonic crystal patterns on a new type of pressure-responsive shape memory polymer (SMP). This approach integrates two disparate fields that do not typically intersect: the well-established templating nanofabrication and shape memory materials. Periodic arrays of polymer macropores templated from self-assembled colloidal crystals are squeezed into disordered arrays in an unusual shape memory "cold" programming process. The recovery of the original macroporous photonic crystal lattices can be triggered by direct writing at ambient conditions using both macroscopic and nanoscopic tools, like a pencil or a nanoindenter. Interestingly, this shape memory disorder-order transition is reversible and the photonic crystal patterns can be erased and regenerated hundreds of times, promising the making of reconfigurable/rewritable nanooptical devices. Quantitative insights into the shape memory recovery of collapsed macropores induced by the lateral shear stresses in direct writing are gained through fundamental investigations on important process parameters, including the tip material, the critical pressure and writing speed for triggering the recovery of the deformed macropores, and the minimal feature size that can be directly written on the SMP membranes. Besides straightforward applications in photonic crystal devices, these smart mechanochromic SMPs that are sensitive to various mechanical stresses could render important technological applications ranging from chromogenic stress and impact sensors to rewritable high-density optical data storage media.

Optically Bistable Macroporous Photonic Crystals Enabled by Thermoresponsive Shape Memory Polymers

Macroporous photonic crystals with optically bistable states have been fabricated by using thermoresponsive shape memory polymers. The reversible transition between an ordered permanent state and a disordered temporary state results in tremendous changes in the appearance and the optical properties of the membranes. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Macroporous photonic crystal-based vapor detectors created by doctor blade coating

We report the achievement of rapid and reversible vapor detection by using 3D macroporous photonic crystals created by a continuous and scalable bottom-up technology. Capillary condensation of a condensable vapor in the interconnected macropores with ∼74% porosity leads to the increase of the effective refractive index of the diffractive medium, resulting in the redshift of the optical stop bands. The wavelength shift is linearly proportional to the vapor partial pressure for a spectrum of vapors. Optical simulation and theoretical prediction based on Kelvin equation suggest that a liquid film is formed on the walls of the macropores during vapor condensation.

Excellent mechanical properties of three-dimensionally ordered macroporous nickel photonic crystals

High quality three-dimensionally ordered macroporous (3DOM) nickel photonic crystals (PCs) are fabricated using the polystyrene template-assisted electrodeposition method on nickel alloy substrate. The Ni 2+ in solution will firstly arrive in the electrode (nickel alloy substrate) and occupy the interstices among the PS template spheres; when enlarge the deposition time to 5 min, 3DOM nickel PCs will be achieved. The 3DOM nickel PCs grow firmly on the substrate due to the similar bounds between the PCs and substrate. Excellent mechanical properties are observed in the 3DOM nickel PCs, which may promote the practical applications of PCs.

Band Gap Tuning of Macro-Porous Si Photonic Crystals by Thermally Grown SiO2 Interfacial Layer

By plane wave expansion method (PWM) we modeled the effects of thermal oxidation and oxide etching on Si photonic crystals (PCs) of triangular lattice and proposed that these two processes can be extremely advantageous methods for tuning the photonic band gap and defect frequency. Two dimensional photonic crystals consisting of air cylinders in silicon background are studied before and after oxidation and partial oxide etching. Before oxidation the absolute band gap can be tuned only in a small range of radii (0.404a-0.48a); a is the lattice constant. Within this range, the band gap changes rapidly with the air cylinder radius due to the high dielectric constant of silicon. When thermal oxide interfacial layers are incorporated, the band gap can be tuned by varying the oxide thickness in the range of (0.26a-0.48a). By supercell method, formation of a defect level inside the band gap by means of the interfacial oxide layer and tuning of the defect frequency by varying the oxide thickness are also studied. A monopole defect mode is observed by oxidizing the center cylinder in a 5x5 suppercell of silicon cylinders with radius 0.28a in air background. The defect frequency is tuned by varying the oxide thickness from 0.15a to 0.3a.

Band Gap Tuning of Macro-Porous Si Photonic Crystals by Thermally Grown SiO2 Interfacial Layer

not Available.

Preparation of a three-dimensional ordered macroporous titanium dioxide material with polystyrene colloid crystal as a template

Polystyrene (PS) photonic colloid crystals were assembled from PS spheres prepared by emulsion-free polymerization through an improved vertical deposition method that could shorten the assembly time efficiently. The monodispersity of the spheres was appraised according to the standard deviation. The results showed that the PS spheres had a high monodispersity with a standard deviation of 3.7% and a dispersion coefficient of 0.02. The morphology and bandgap structure were observed with scanning electron microscopy images and transmission spectra, respectively. The mechanism of vertical deposition was analyzed simply. As an application of PS colloid crystals, ordered macroporous TiO2 photonic crystals were prepared, and the structure and properties of macroporous TiO2 were also studied with various analytical methods, which provided some values for the fabrication of photonic crystals with a complete bandgap. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008