Chromogenic Photonic Crystal Sensors Enabled by Multistimuli-Responsive Shape Memory Polymers.

Here novel chromogenic photonic crystal sensors based on smart shape memory polymers (SMPs) comprising polyester/polyether-based urethane acrylates blended with tripropylene glycol diacrylate are reported, which exhibit nontraditional all-room-temperature shape memory (SM) effects. Stepwise recovery of the collapsed macropores with 350 nm diameter created by a "cold" programming process leads to easily perceived color changes that can be correlated with the concentrations of swelling analytes in complex, multicomponent nonswelling mixtures. High sensitivity (as low as 10 ppm) and unprecedented measurement range (from 10 ppm to 30 vol%) for analyzing ethanol in octane and gasoline have been demonstrated by leveraging colorimetric sensing in both liquid and gas phases. Proof-of-concept tests for specifically detecting ethanol in consumer medical and healthcare products have also been demonstrated. These sensors are inexpensive, reusable, durable, and readily deployable with mobile platforms for quantitative analysis. Additionally, theoretical modeling of solvent diffusion in macroporous SMPs provides fundamental insights into the mechanisms of nanoscopic SM recovery, which is a topic that has received little examination. These novel sensors are of great technological importance in a wide spectrum of applications ranging from environmental monitoring and workplace hazard identification to threat detection and process/product control in chemical, petroleum, and pharmaceutical industries.

Polymeric micelle assembly for preparation of large-sized mesoporous metal oxides with various compositions.

Here we report the synthesis of mesoporous metal oxide materials with various compositions by assembly of spherical polymeric micelles consisting of triblock copolymer poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-b-PVP-b-PEO) with three chemically distinct units. The PVP block interacts strongly with the inorganic precursors for the target compositions. The hydrophobic PS block is kinetically frozen in the precursor solutions, enabling the spherical micelles to remain in a stable form. The frozen PS cores serve as templates for preparing robust mesoporous materials. The PEO corona helps the micelles to stay well dispersed in the precursor solutions, which plays a key role in the orderly arrangement of the micelles during solvent evaporation. This approach is based on assembly of the stable micelles using a simple, highly reproducible method and is widely applicable toward numerous compositions that are difficult for the formation of mesoporous structures.

Water-based synthesis of zeolitic imidazolate framework-90 (ZIF-90) with a controllable particle size.

The ZIF code: ZIF-90 materials were successfully synthesized in an optimized water-based system. The particle size, ranging from micro- to nanoscales, could be controlled by different amounts of polyvinylpyrrolidone (PVP), Zn/imidazole-2-carboxaldehyde ratio and alcohol.

Superhydrophobic hierarchical arrays fabricated by a scalable colloidal lithography approach.

Here we report an unconventional colloidal lithography approach for fabricating a variety of periodic polymer nanostructures with tunable geometries and hydrophobic properties. Wafer-sized, double-layer, non-close-packed silica colloidal crystal embedded in a polymer matrix is first assembled by a scalable spin-coating technology. The unusual non-close-packed crystal structure combined with a thin polymer film separating the top and the bottom colloidal layers render great versatility in templating periodic nanostructures, including arrays of nanovoids, nanorings, and hierarchical nanovoids. These different geometries result in varied fractions of entrapped air in between the templated nanostructures, which in turn lead to different apparent water contact angles. Superhydrophobic surfaces with >150° water contact angles and <5° contact angle hysteresis are achieved on fluorosilane-modified polymer hierarchical nanovoid arrays with large fractions of entrapped air. The experimental contact angle measurements are complemented with theoretical predictions using the Cassie's model to gain insights into the fundamental microstructure-dewetting property relationships. The experimental and theoretical contact angles follow the same trends as determined by the unique hierarchical structures of the templated periodic arrays.

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.

Rapid electrostatics-assisted layer-by-layer assembly of near-infrared-active colloidal photonic crystals.

Here we report a rapid and scalable bottom-up technique for layer-by-layer (LBL) assembling near-infrared-active colloidal photonic crystals consisting of large (⩾1µm) silica microspheres. By combining a new electrostatics-assisted colloidal transferring approach with spontaneous colloidal crystallization at an air/water interface, we have demonstrated that the crystal transfer speed of traditional Langmuir-Blodgett-based colloidal assembly technologies can be enhanced by nearly 2 orders of magnitude. Importantly, the crystalline quality of the resultant photonic crystals is not compromised by this rapid colloidal assembly approach. They exhibit thickness-dependent near-infrared stop bands and well-defined Fabry-Perot fringes in the specular transmission and reflection spectra, which match well with the theoretical calculations using a scalar-wave approximation model and Fabry-Perot analysis. This simple yet scalable bottom-up technology can significantly improve the throughput in assembling large-area, multilayer colloidal crystals, which are of great technological importance in a variety of optical and non-optical applications ranging from all-optical integrated circuits to tissue engineering.

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.

Reconfigurable photonic crystals enabled by pressure-responsive shape-memory polymers.

Smart shape-memory polymers can memorize and recover their permanent shape in response to an external stimulus (for example, heat). They have been extensively exploited for a wide spectrum of applications ranging from biomedical devices to aerospace morphing structures. However, most of the existing shape-memory polymers are thermoresponsive and their performance is hindered by heat-demanding programming and recovery steps. Although pressure is an easily adjustable process variable such as temperature, pressure-responsive shape-memory polymers are largely unexplored. Here we report a series of shape-memory polymers that enable unusual 'cold' programming and instantaneous shape recovery triggered by applying a contact pressure at ambient conditions. Moreover, the interdisciplinary integration of scientific principles drawn from two disparate fields--the fast-growing photonic crystal and shape-memory polymer technologies--enables fabrication of reconfigurable photonic crystals and simultaneously provides a simple and sensitive optical technique for investigating the intriguing shape-memory effects at nanoscale.

Chromogenic Photonic Crystals Enabled by Novel Vapor-Responsive Shape-Memory Polymers.

A new type of shape-memory polymer (SMP) is developed by integrating scientific principles drawn from two disparate fields: the fast-growing photonic crystal and SMP technologies. This new SMP enables room-temperature operation for the entire shape-memory cycle and instantaneous shape recovery triggered by exposure to a variety of organic vapors.

Highly crystallized nanometer-sized zeolite a with large Cs adsorption capability for the decontamination of water.

Nanometer-sized zeolite A with a large cesium (Cs) uptake capability is prepared through a simple post-milling recrystallization method. This method is suitable for producing nanometer-sized zeolite in large scale, as additional organic compounds are not needed to control zeolite nucleation and crystal growth. Herein, we perform a quartz crystal microbalance (QCM) study to evaluate the uptake ability of Cs ions by zeolite, to the best of our knowledge, for the first time. In comparison to micrometer-sized zeolite A, nanometer-sized zeolite A can rapidly accommodate a larger amount of Cs ions into the zeolite crystal structure, owing to its high external surface area. Nanometer-sized zeolite is a promising candidate for the removal of radioactive Cs ions from polluted water. Our QCM study on Cs adsorption uptake behavior provides the information of adsorption kinetics (e.g., adsorption amounts and rates). This technique is applicable to other zeolites, which will be highly valuable for further consideration of radioactive Cs removal in the future.