Crystalline Colloidal Array Research Articles

High-Sensitivity Mechanochromic Sensor Using Core-Shell Colloidal Crystals

The Colloidal Crystals-based mechanochromic sensor changes color as the arrangement of colloidal particles changes in response to mechanical deformation, which can be detected through optical measurement. This type of sensor can be used in various applications, such as automobile collision detection, structural deformation detection, and medical equipment, among others. In this study, we prepared a stretchable film by dispersing surface-functionalized colloidal particles in an elastic polymer matrix. Surface of silica colloidal particle was modified with an initiator for Atom Transfer Radical Polymerization (ATRP), followed by surface-initiated ATRP of poly(t-butyl methacrylate) (PtBMA). The core-shell colloidal particles were composited with various acrylic monomers, to fabricate crystalline colloidal array which transforms to elastic film by photopolymerization exhibiting structural color. The prepared film showed a clear color change for deformation within 10%, and the peak reflectance showed more than 30%.

Radioluminescent Photonic Bandgap Hydrogels: Mechanochromic Tunable Emissions.

Fully organic, radioluminescent crystalline colloidal arrays (CCAs) with covalently incorporated emitters were synthesized by using up to three organic fluorophores that were Förster resonance energy transfer (FRET) pairs with each other. The emitters were covalently incorporated into monodisperse poly(styrene-co-propargyl acrylate) nanoparticles in various combinations, resulting in blue-, green-, and red-emitting CCAs when excited with an X-ray source. The negatively charged surfaces of the monodisperse nanoparticles caused self-assembly into a crystal-like structure, which resulted in a partial photonic bandgap (i.e., rejection wavelength) within the near-visible and visible light spectrum. When the rejection wavelength of the CCA overlapped its radioluminescence, the spontaneous emission was inhibited and the emission intensity decreased. A poly(ethylene glycol) methacrylate-based hydrogel network was used to encapsulate the CCAs and stabilize their crystal-like structure. Within the hydrogel, coupling the photonic bandgap with the radioluminescence of the CCA films led to robust optical systems with tunable emissions. These fully organic, hydrogel-stabilized, radioluminescent CCAs possess mechanochromic tunable optical characteristics with future applications as potentially less toxic X-ray bioimaging materials.

A photonic crystal material for the online detection of nonpolar hydrocarbon vapors.

A modern level of nanotechnology allows us to create conceptually new test systems for chemical analyses and to develop sensitive and compact sensors for various types of substances. However, at present, there are very few commercially available compact sensors for the determination of toxic and carcinogenic substances, such as organic solvents that are used in some construction materials. This article contains an overview of how 3D photonic crystals are used for the creation of a new test system for nonpolar organic solvents. The morphology and structural parameters of the photonic crystals, based upon a crystalline colloidal array with a sensing matrix of polydimethylsiloxane, have been determined by using scanning electron microscopy and by the results of specular reflectance spectroscopy based on the Bragg–Snell law. A new approach has been proposed for the application of this sensor in chemical analysis for the qualitative detection of saturated vapors of volatile organic compounds due to configuration changes of the photonic bandgap, recorded by diffuse reflectance spectroscopy. The exposure of the sensor to aromatic (benzene, toluene and p-xylene) and aliphatic (n-pentane, n-heptane, n-octane and n-decane) hydrocarbons has been analyzed. The reconstitution of spectral parameters of the sensor during the periodic detection of saturated vapors of toluene has been evaluated.

Photonic Microbeads Templated by Oil-in-Oil Emulsion Droplets for High Saturation of Structural Colors.

Photonic microbeads containing crystalline colloidal arrays are promising as a key component of structural-color inks for various applications including printings, paintings, and cosmetics. However, structural colors from microbeads usually have low color saturation and the production of the beads requires delicate and time-consuming protocols. Herein, elastic photonic microbeads are designed with enhanced color saturation through facile photocuring of oil-in-oil emulsion droplets. Dispersions of highly-concentrated silica particles in elastomer precursors are microfluidically emulsified into immiscible oil to produce monodisperse droplets. The silica particles spontaneously form crystalline arrays in the entire volume of the droplets due to interparticle repulsion which is unperturbed by the diffusion of the surrounding oil whereas weakened for oil-in-water droplets. The crystalline arrays are permanently stabilized by photopolymerization of the precursor, forming elastic photonic microbeads. The microbeads are transferred into the refractive-index-matched biocompatible oil. The high crystallinity of colloidal arrays increases the reflectivity at stopband and the index matching reduces incoherent scattering at the surface of the microbeads, enhancing color saturation. The colors can be adjusted by mixing two distinctly colored microbeads. Also, low stiffness and high elasticity reduce foreign-body sensation and enhance fluidity, potentially serving as pragmatic structural colorants for photonic inks.

Full‐Color Electrophoretic Display Using Charged Colloidal Arrays of Core–Shell Microspheres with Enhanced Color Tunability in Non‐Polar Medium

AbstractIn this study, core–shell microspheres of poly(methylmethacrylate) (PMMA) and poly(t‐butylmethacrylate) (PtBMA) are synthesized and dispersed in a non‐polar medium exhibiting a structural color in the visible range. The charge stabilization of the PMMA–PtBMA microsphere is achieved because of preferential adsorption of the charged inverse micelles of aerosol‐OT (AOT) on the microsphere surface. While the PtBMA shell enables the dispersion of the microspheres in isoparaffinic fluid, the PMMA core provides an enhanced refractive index contrast with the medium. In comparison to PtBMA‐only microsphere, incorporation of PMMA core not only increases the average refractive index but also increases the surface charge density of the microsphere, which is attributed to strong attraction between the inverse micelles and the microsphere. The optimized crystalline colloidal array (CCA) of the PMMA–PtBMA microsphere shows stronger structural colors than those of the PtBMA‐only spheres because of an enhanced index contrast with the liquid medium, and an improved color tunability is also achieved. A CCA exhibits approximately 50% light transmittance, demonstrating a semi‐transparent display. The repeated voltage biases proved that a CCA has excellent stability. Finally, a low‐angular dependency of the PMMA–PtBMA CCA is confirmed, which is an advantageous feature as an electrophoretic display.

The diffraction behavior of crystalline colloidal arrays formed by poly(styrene-co-sodium styrenesulfonate) particles

The diffraction behavior of crystalline colloidal arrays formed by poly(styrene-co-sodium styrenesulfonate) particles

Colorimetric monitoring of humidity by opal photonic hydrogel

The present study demonstrated a new fast colorimetric humidity sensor using the opal hydrogel composite (OHC). First, a highly monodisperse polystyrene (PS) latex was synthesized by soap-free emulsion polymerization and deposited on a glass substrate in order to form a three-dimensional opal photonic crystal. Then, the homogenous hydrogel precursor was infiltrated into the interstitial space of opal by capillary forces and underwent chemical polymerization to construct an embedded PS crystalline colloidal array within a poly (acrylamide-co-acrylic acid) hydrogel network. The scanning electron microscopic images confirmed the formation of opal structures. An interesting feature of the presented OHC sensor is that the sensor is transparent in a dry state and an increase in relative humidity (RH) leads to a colorful film. In addition, UV/Vis spectroscopy was performed within an RH range of 25–95%, indicating that reflection peak height gradually develops by RH increasing and the peak position shifts from 413 to 518 nm. Further, the sensor functions extremely rapidly and changes its color by increasing RH within a few seconds (less than 3 s) and becomes transparent again quickly as humidity represents a decrease. Based on the results, repeated humidity changes revealed that the sensor has an excellent reproducibility without any reduction in response time and sensitivity or a color change. Finally, it has good adhesion to the glass substrate which makes it a suitable RH sensor in different applications, along with the rapid response time, high sensitivity, repeatability, and the visual alarm.

Reversible Colloidal Crystallization

We report 3D colloidal self-assembly (crystallization) of poly(ionic liquid) latexes to produce crystals that exhibit reversible melting and recrystallization in water, due to “classical” interparticle interactions, typical of multifunctional polymers. These new materials are derived from an ionic liquid monomer that is polymerized at room temperature by redox-initiated polymerization. Particle synthesis, self-assembly, thermal properties, and introductory light diffraction effects are reported with a focus on melting. These crystals are distinguishable from classical colloidal crystalline arrays, and are the first such crystals to exhibit thermal melting. This new hydrogel offers promise for engineering large volume production of photonic crystals active in the visible and proximal spectral regions, by crystallization from suspension (solution), characteristic of most useful chemical compounds.

Self-Healable Poly(vinyl alcohol) Photonic Crystal Hydrogel

A self-healable poly(vinyl alcohol) (PVA) gelated crystalline colloidal array (GCCA) photonic crystal hydrogel was presented. The GCCA material efficiently diffracted visible light, and the structu...

Photonic nanostructures of nanodiscs with multiple magneto-optical properties

We demonstrate the modulation of multiple optical properties by a single stimulus in crystalline colloidal arrays of two-dimensional magnetic nanodiscs.

A Butterfly-Inspired Hierarchical Light-Trapping Structure towards a High-Performance Polarization-Sensitive Perovskite Photodetector.

Extensive applications for photodetectors have led to demand for high-responsivity polarization-sensitive light detection. Inspired by the elaborate architecture of butterfly Papilio paris, a 1D nanograting bonded porous 2D photonic crystal perovskite photodetector (G-PC-PD) using a commercial DVD master and 2D crystalline colloidal arrays template was fabricated. The coupling effect from grating diffraction and reflection of the PC stopband renders the enhanced light harvesting of G-PC-PD. The porous scaffold and nanoimprinting process afford a highly crystalline perovskite film. White light responsivity and detectivity of G-PC-PD are up to 12.67 A W-1 and 3.22×1013 Jones (6∼7 times that of a pristine perovskite photodetector). The highly ordered nanograting arrays of G-PC-PD enable polarization-sensitive light detection with a rate of -0.72 nA deg-1 . This hierarchical perovskite integrated nanograting and 2D PC architecture opens a new avenue to high-performance optoelectronic devices.

A Butterfly‐Inspired Hierarchical Light‐Trapping Structure towards a High‐Performance Polarization‐Sensitive Perovskite Photodetector

AbstractExtensive applications for photodetectors have led to demand for high‐responsivity polarization‐sensitive light detection. Inspired by the elaborate architecture of butterfly Papilio paris, a 1D nanograting bonded porous 2D photonic crystal perovskite photodetector (G‐PC‐PD) using a commercial DVD master and 2D crystalline colloidal arrays template was fabricated. The coupling effect from grating diffraction and reflection of the PC stopband renders the enhanced light harvesting of G‐PC‐PD. The porous scaffold and nanoimprinting process afford a highly crystalline perovskite film. White light responsivity and detectivity of G‐PC‐PD are up to 12.67 A W−1 and 3.22×1013 Jones (6∼7 times that of a pristine perovskite photodetector). The highly ordered nanograting arrays of G‐PC‐PD enable polarization‐sensitive light detection with a rate of −0.72 nA deg−1. This hierarchical perovskite integrated nanograting and 2D PC architecture opens a new avenue to high‐performance optoelectronic devices.

Clinical Evaluation of a Photonic Crystal Sensor for Glucose Monitoring in Urine

AbstractSelf‐monitoring of blood glucose is not only an effective method to treat diabetes, but also a painful invasive process to patients. To develop a noninvasive technique, we evaluated the clinical performance of a polymerized crystalline colloidal array (PCCA) sensor for glucose monitoring in urine. A two‐dimensional crystalline colloidal array (CCA) was assembled using polystyrene particles and further embedded into 3‐acrylamidophenylboronic acid functionalized hydrogel. 101 urine samples were tested, and the glucose concentrations was calculated by the particle spacing of PCCA. All the urine samples were also analyzed by automated urine analyzers. Pearson correlation and linear regression analyses showed a linear relationship between the PCCA results with a range of 0.4‐53.3 mmol L−1 and the Cobas® 8000 references (r=0.914; [PCCA]=0.9281 [HK] + 2.0585 mmol L−1). Cohen's kappa (κ) statistic with 0.65 (sig < 0.05) showed the PCCA results had moderate agreement with references. Also, Bland‐Altman plot showed that AX‐4030 sensor's systematic error was higher than PCCA sensor (mean=7.4813 > 0.5271 mmol L−1). The PCCA urine glucose biosensor has the advantages of fast fabrication, low cost, easy operation and high sensitivity, which provides a promising technique for noninvasive point‐of‐care glucose monitoring.

Single-Stimulus-Induced Modulation of Multiple Optical Properties.

Stimuli-responsive smart optical materials hold great promise for applications in active optics, display, sensing, energy conversion, military camouflage, and artificial intelligence. However, their applications are greatly restricted by the difficulty of tuning different optical properties within the same material, especially by a single stimulus. Here, magnetic modulations of multiple optical properties are demonstrated in a crystalline colloidal array (CCA) of magnetic nanorods. Small-angle X-ray scattering studies reveal that these nanorods form an unusual monoclinic crystal in concentrated suspensions. The CCA exhibits optical anisotropy in the form of a photonic bandgap and birefringence, thus enabling magnetic tuning of the structural color and transmittance at a rate of 50 Hz. As a proof-of-concept, it is further demonstrated that the fabrication of a multifunctional device for display, anticounterfeiting, and smart-window applications based on this multiple magneto-optical effect. The study not only provides a new model system for understanding colloidal assembly, but also opens up opportunities for new applications of smart optical materials for various purposes.

X-ray radioluminescent hydrogel stabilized crystalline colloidal arrays

The current effort utilizes methacrylate based hydrogels derived from polystyrene-co-poly(propargyl)acrylate (PS-pPA) colloidal particles with encapsulated stilbene, an organic scintillator, as an x-ray activated imaging agent. These nanoparticles self-assemble into electrostatically stabilized crystalline colloidal arrays (CCAs). Upon photo-polymerization into the hydrogel, the material remains ordered where the crystal is stabilized and more mechanically robust. Upon x-ray stimulation, stilbene/PS-pPA hydrogels emit blue light. While stilbene is an x-ray active material, it remains a poor emitter under x-ray irradiation. However, the color and amount of light emitted from stilbene/PS-pPA could be manipulated through judicious choice in fluorophores that form FRET pairs to span the visible spectrum. To this end, a copper(I) catalyzed azide/alkyne cycloaddition (CuAAC) reaction was employed to covalently attach an azide modified naphthalimide (AzNap) derivative to the particles all while being in hydrogel form. Stilbene and AzNap are FRET pairs with one another, which resulted in an increase of the total luminescence of the system; these hydrogels now emit green light. In addition, the original stilbene/PS-pPA hydrogels could be functionalized with both AzNap and an azide modified rhodamine B derivative (AzRhod), which are FRET pairs with each other, through CuAAC reactions in the hydrogel. These hydrogels emit orange light and the overall luminescence is similar to that of the AzNap functionalized hydrogels even through two energy transfers. These fully organic hydrogels may be suitable alternatives to toxic inorganic materials in x-ray based imaging techniques.

Dynamic Emission Tuning of X‐ray Radioluminescent Crystalline Colloidal Arrays: Coupling the Optical Stop Band with Sequential Förster Resonance Energy Transfers

AbstractX‐ray radiation exhibits diminished scattering and a greater penetration depth in tissue relative to the visible spectrum and has spawned new medical imaging techniques that exploit X‐ray luminescence of nanoparticles. The majority of the nanoparticles finding applications in this field incorporate metals with high atomic numbers and pose potential toxicity effects. Here, a general strategy for the preparation of a fully organic X‐ray radioluminescent colloidal platform that can be tailored to emit anywhere in the visible spectrum through a judicious choice in donor/acceptor pairing and multiple sequential Förster resonance energy transfers (FRETs) is presented. This is demonstrated with three different types of ≈100 nm particles that are doped with anthracene as the scintillating molecule to “pump” subsequent FRET dye pairs that result in emissions from ≈400 nm out past 700 nm. The particles can be self‐assembled in crystalline colloidal arrays, and the radioluminescence of the particles can be dynamically tuned by coupling the observed rejection wavelength with the dyes' emission.

Vivid structural colors from long-range ordered and carbon-integrated colloidal photonic crystals.

A facile strategy to prepare high-quality colloidal photonic crystals (PCs) with good visibility is proposed. Based on a high refractive-index material (zinc sulfide), highly monodispersed colloidal particles are successfully produced and assembled into long-range ordered crystalline colloidal arrays. The carbon-based materials are in situ incorporated with the long-range ordered colloidal PCs, which endows PCs with the combined characteristics to simultaneously achieve an intense photonic stop band and excellent control of incoherent light scattering. Owing to these merits, the obtained ZnS colloidal PCs have demonstrated strong brightness with the maximum reflectivity of 98%. Moreover, the coloration, saturation, and viewing angle are all improved. This study provides a straightforward and cost-effective strategy to create structural colors with high-quality visibility, which is expected to facilitate future applications of colloidal PCs.

Low-Power All-Organic Electrophoretic Display Using Self-Assembled Charged Poly( t-butyl methacrylate) Microspheres in Isoparaffinic Fluid.

The increasing demands for display devices with low power consumption and outdoor readability have stimulated comprehensive research into full-color reflective displays that employ color-tunable photonic crystal technologies. Although the recently developed crystalline colloidal arrays (CCAs) of the charged microspheres have shown the outstanding color tunability, the practical application is limited because the use of highly polar liquid medium such as water is required to maintain the charges on the surface of microsphere, whereas it is not suitable for long-term use in an electric field. Herein, a self-assembled CCA from charged poly( t-butyl methacrylate) microspheres was successfully fabricated, which was stabilized by the charged inverse micelles of sodium di-2-ethylhexyl-sulfosuccinate in a nonpolar isoparaffinic fluid. A charged all-organic CCA was found to exhibit full-color tunability with a 1000-fold reduction in the power consumption (∼6 μW cm-2) under a direct current voltage bias of 4 V in comparison to that in an aqueous system, which is a promising feature for a low-power-consumption display device.

Enhanced Optical Sensitivity in Thermoresponsive Photonic Crystal Hydrogels by Operating Near the Phase Transition.

Photonic crystal hydrogels composed of analyte-responsive hydrogels and crystalline colloidal arrays have immense potential as reagentless chemical and biological sensors. In this work, we investigated a general mechanism to rationally tune the sensitivity of photonic crystal hydrogels consisting of stimuli-responsive polymers to small molecule analytes. This mechanism was based on modulating the demixing temperature of such hydrogels relative to the characterization temperature to in effect maximize the extent of phase separation behavior; thus, the volume changes in response to the target analytes. Using ethanol as a model analyte, we demonstrated that this mechanism led to a dramatic increase in the sensitivity of optically diffracting poly(N-isopropylacrylamide) (pNIPAM) hydrogel films that exhibit a lower critical solution temperature (LCST) behavior. The demixing temperature of the pNIPAM films was modulated by copolymerization of the films with relatively hydrophobic and hydrophilic comonomers, as well as by varying the ionic strength of the characterization solution. Our results showed that copolymerization of the films with 2.5 mol % of N-tert-butylacrylamide, which is hydrophobic relative to pNIPAM, enabled the detection limit of the pNIPAM films to ethanol to be lowered ∼2-fold at 30 °C. Additionally, increasing the ionic strength of the characterization solution above 200 mM resulted in a dramatic increase in the extent of contraction of the films in the presence of ethanol. Ultimately, it was demonstrated that as little as 16 g/L or 2 vol % of ethanol in water could reliably be detected, and that the sensitivity of the films to ethanol was predictably greatest when operating near the phase transition, such that even small additions of the analyte induced the start of demixing and the collapse of the hydrogel. Such a mechanism may be extended to photonic crystal hydrogel sensors prepared from other stimuli-responsive polymers and more broadly exploited to enhance the utility of these sensors for a broad range of analytes.

Effect of surface modified of phenolic resin nanospheres on the structural color under electric field

ABSTRACTAn electrically tunable photonic crystal is developed utilizing crystalline colloidal arrays of particles with low density and high optical contrast. Through modulation of the charge on the surface of particle, and the applied electric field, the peak position of the reflection changes with the increasing voltage. The possibility of using phenolic resin to realize the full color modulation was obtained, which paves a way to develop a novel reflective display with organic nanospheres.