Crystalline Colloidal Array Research Articles

Langevin Dynamics Simulation of 3D Colloidal Crystal Vacancies and Phase Transitions

We study the mechanism of vacancy migration and phase transitions of 3D crystalline colloidal arrays (CCA) using Langevin dynamics simulations. We calculate the self-diffusion coefficient of the colloid particles and the diffusion constant for vacancies as a function of temperature and DLVO potential parameters. We investigate the phase behavior of several systems with different interaction potential parameters using Voronoi analysis. Voronoi polyhedra tessellation, which is a useful method for characterizing the nearest neighbor environment around each atom, provides an efficient and effective way to identify phase transitions as well as geometrical changes in crystals. Using Voronoi analysis, we show that several neighboring particles are involved in the vacancy migration process that causes the vacancy to diffuse.

Construction of near-infrared photonic crystal glucose-sensing materials for ratiometric sensing of glucose in tears

Noninvasive monitoring of glucose in tears is highly desirable in tight glucose control. The polymerized crystalline colloidal array (PCCA) that can be incorporated into contact lens represents one of the most promising materials for noninvasive monitoring of glucose in tears. However, low sensitivity and slow time response of the PCCA reported in previous arts has limited its clinical utility. This paper presents a new PCCA, denoted as NIR–PCCA, comprising a CCA of glucose-responsive sub-micrometered poly(styrene-co-acrylamide-co-3-acrylamidophenylboronic acid) microgels embedded within a slightly positive charged hydrogel matrix of poly(acrylamide-co-2-(dimethylamino)ethyl acrylate). This newly designed NIR–PCCA can reflect near-infrared (NIR) light, whose intensity (at 1722nm) would decrease evidently with increasing glucose concentration over the physiologically relevant range in tears. The lowest glucose concentration reliably detectable was as low as ca. 6.1μg/dL. The characteristic response time τsensing was 22.1±0.2s when adding glucose to 7.5mg/dL, and the higher the glucose concentration is, the faster the time response. Such a rationally designed NIR–PCCA is well suited for ratiometric NIR sensing of tear glucose under physiological conditions, thereby likely to bring this promising glucose-sensing material to the forefront of analytical devices for diabetes.

Vertical spreading of two-dimensional crystalline colloidal arrays

We report on a novel self-driven climbing of two-dimensional (2-D) ordered monolayer crystalline colloidal arrays (CCAs). This phenomenon can be used to rapidly and efficiently prepare large area, highly ordered 2-D array monolayer CCA films on various substrates. Large area 2-D polystyrene (PS) particle CCAs were fabricated on water surfaces by a needle tip flow technique. Introduction of a wet substrate through the 2-D particle monolayer array on the water surface causes the 2-D array to flow onto the wet substrate surface due to a surface spreading pressure. This method can quickly prepare ordered 2-D particle arrays on numerous wet substrates including flat/curved glass slides, inner walls of glass tubes, hydrogels, flexible polymer films, patterned surfaces, etc. By using responsive hydrogels as substrates, we can conveniently prepare 2-D photonic crystal sensors that can be used to visually determine analyte concentrations. For example, we prepared 580 nm PS 2-D arrays on poly(2-hydroxyethyl methacrylate) hydrogels to sense ethanol in water.

Electrically tunable photonic crystals from long-range ordered crystalline arrays composed of copolymer colloids

Due to recent growing interest in mobile and e-book devices, new demand for a display with excellent outdoor readability, low power consumption, and reduced eye fatigue has led to research on reflective displays. The crystalline colloidal arrays (CCAs) composed of monodisperse copolymer colloids, investigated in this study, offer great potential for a tunable photonic crystal to be applied to the display technology, owing to its high reflectance and colour purity, as well as to the precise controllability of the photonic colour in a full visible regime. With the help of the manipulability of the particle size and the surface charge, structural colour with improved viewing angle was produced by mixing colloids with different particle sizes. In addition, the stop-band tuning mechanism under the electric field was systematically investigated.

Mutual interaction between embedded microgel particles and the surrounding hydrogel matrix

Polymerized crystalline colloidal array (PCCA) films, i.e., a highly ordered crystalline colloidal array of poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-AAc)) microgel particles embedded in a polyacrylamide (PAAm) hydrogel matrix, were prepared. The interaction between the embedded thermosensitive microgel particles and the non-thermosensitive hydrogel matrix was studied, using the Bragg diffraction of the films as a tool. The intensity and position of the diffraction peak change with temperature, from which important information on the interaction between the microgel particles and the hydrogel matrix was deduced. Our results indicate that the non-thermosensitive, hydrophilic PAAm hydrogel matrix significantly influences the thermosensitive phase transition of the embedded P(NIPAM-AAc) microgel particles. Compared with the freely dispersed microgel particles in solution, only a small change in the volume phase transition temperature of the embedded microgel particles was observed; however, the phase transition becomes less sharp. More importantly, the extent of size change is reduced significantly. On the other hand, the temperature-induced swelling/deswelling of the embedded microgel particles induces a swelling/deswelling of the surrounding hydrogel matrix, revealing that the interaction between the two components is mutual. The temperature-induced swelling/deswelling of the microgel particles is fast; in contrast, the swelling/deswelling of the hydrogel matrix is much slower. The stiffness of the hydrogel matrix affects the interaction between the two components. As the hydrogel matrix becomes stiffer, its influence on the swelling of the microgel particles becomes more prominent. On the other hand, the influence of the microgel particles on the swelling of the hydrogel matrix becomes less prominent.

An imprinted crystalline colloidal array chemical-sensing material for detection of trace diethylstilbestrol

Based on a combination of the molecular imprinting technique and polymerized crystalline colloidal array, we have developed an imprinted crystalline colloidal array (ICCA) chemical-sensing material for the real-time and label-free detection of diethylstilbestrol (DES) in aqueous solution. This novel sensing material was prepared by a noncovalent and self-assembly approach using liquid monodispersed DES-imprinted colloidal spheres and was characterized by a three-dimensional (3D) ordered opal structure in which numerous nanocavities were derived from DES imprinting. Thus, the inherent high affinity of the nanocavities allowed ICCA to recognize DES with high specificity, and changes of the ordered periodic structure enabled ICCA to transfer the recognition events into readable optical signals (label-free). Owing to the special opal structure and without interference from the bulk hydrogel film, the ICCA enabled the rapid and sensitive detection of the target analyte. The understanding of the recognizing response has also been advanced by using molecular modeling software to compute rational interaction between the template molecules and the function monomers. After careful optimization of the assay conditions, the ICCA could decrease its diffraction intensity within just 7 min according to the DES concentration from 2 ng mL(-1) to 8.192 μg mL(-1), whereas there were no obvious diffraction intensity changes for the DES analogues. The adsorption results showed that the homogenous structure and large surface area of ICCA could improve its adsorption capacity. Therefore, such a sensing material with high selectivity, high sensitivity, high stability, and easy operation might offer an attractive alternative for establishing optical sensors for the rapid real-time monitoring of different residues in food and the environment.

Facile and controllable fabrication of three-dimensionally quasi-ordered macroporous TiO2 for high performance lithium-ion battery applications

A facile and controllable strategy for preparing three-dimensionally quasi-ordered macroporous (3DOM) TiO2 has been developed through in situ hydrolysis on poly(vinyl alcohol) (PVA) gelated crystalline colloidal array (GCCA) photonic crystal films. The presence of PVA hydrogel in the PVA GCCA results in a non-close-packed structure and an increase in the hydrophilic character of the template, which contribute to a more uniform wetting of the template during the infiltration process. The resulting 3DOM TiO2 as an anode material for lithium-ion batteries (LIBs) exhibits a high rate capability and excellent cycle performance. The method presented in this paper is versatile and can be expanded for preparing various quasi-order macroporous materials.

Non-invasive in vivo imaging of the ionic regimes along the gastrointestinal tract of a freshwater vertebrate model organism (Japanese medaka) using responsive photonic crystal beads.

Microspherical photonic colloidal crystalline beads that are responsive to media ionic strength of cationic electrolytes have been developed for in vivo imaging of the morphology and concentration gradient of cationic electrolytes along the gastrointestinal (GI) tract of live Japanese medaka (Oryzias latipes). These responsive photonic beads were assembled from core-shell nano-sized particles with polystyrene-co-polyacrylic acid (PS-co-PAA) cores and poly(hydroxyethyl methacrylate-co-p-styrene sulfonate) (PHEMA-co-PSS) hydrogel shells. The three-dimensional orderly packing of these nano-sized core-shell particles gave rise to the photonic properties of the resultant colloidal crystalline array of microspheres. The cationic electrolyte-induced volume phase transition of the sulfonate-laden hydrogel shells of the nano-sized particles altered the lattice spacing among those particles and brought about the photonic responses of the colloidal crystalline beads. Unambiguous changes in the diffraction colour of the colloidal crystalline beads were observable under ordinary ambient light in solution media of increasing concentration of sodium chloride up to 500 mM. These photonic colloidal crystalline beads were found to possess enough structural integrity for in vivo imaging of the GI tract of live Japanese medaka. With the use of a conventional optical microscope, the gradient in the ionic strength of cationic electrolytes along the GI tract of live Japanese medaka larvae was readily revealed, with a lower electrolyte concentration in the mid-intestine (<50 mM) compared to that of the posterior-intestine (≥50 mM). Our results demonstrated the potential of stimuli-responsive photonic materials in bio-imaging applications.

Glucose-sensitivity of core-shell microspheres and their crystalline colloidal arrays

Thermoresponsive core-shell microspheres are prepared and functionalized with 3-aminophenylboronic acid to make them responsive to glucose. The volume phase transition of the resulting particles is shifted to a lower temperature and a clear swelling is caused by the presence of glucose. The particles after the functionalization preserved their capability to form crystalline colloidal arrays. The changes of their properties may be used in the design of glucose sensors.

A Combined Physical–Chemical Polymerization Process for Fabrication of Nanoparticle–Hydrogel Sensing Materials

A new type of light diffracting hydrogel composite film consisting of nanoparticles and polymer has been fabricated through a combined physical–chemical polymerization process. In this fabrication approach, polymers with ionic functional groups for molecular recognition were successfully incorporated into a hydrogel of colloidal photonic crystals. We first embedded crystalline colloidal arrays into a nonionic polymer hydrogel by a physical freeze–thaw process using a formulation that contained poly(vinyl alcohol), dimethyl sulfoxide, water, and monodispersed polystyrene nanoparticles. Then, a second ionic polymer network, which interpenetrates into the first polymer network, was formed through a photochemical polymerization process. During the formation of the second polymer network, functional groups for molecular recognition were introduced. Finally, the physically cross-linked nonionic polymer network was removed by hydrothermal dissolution, leaving the chemically cross-linked ionic polymer network int...

Full Color Tunable Photonic Crystal from Crystalline Colloidal Arrays with an Engineered Photonic Stop‐Band

An electrically tunable photonic crystal is developed utilizing crystalline colloidal arrays of high refractive index particles. Through modulation of the refractive index of the particle, and the applied electric field, both the bandwidth and position of the photonic bandgap could be tuned. Full color modulation with high optical quality is achieved, which paves a way to develop a novel reflective display.

Two-Dimensional Photonic Crystal Surfactant Detection

We developed a novel two-dimensional (2-D) crystalline colloidal array photonic crystal sensing material for the visual detection of amphiphilic molecules in water. A close-packed polystyrene 2-D array monolayer was embedded in a poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogel film. These 2-D photonic crystals placed on a mirror show intense diffraction that enables them to be used for visual determination of analytes. Binding of surfactant molecules attaches ions to the sensor that swells the PNIPAAm-based hydrogel. The resulting increase in particle spacing red shifts the 2-D diffracted light. Incorporation of more hydrophobic monomers increases the sensitivity to surfactants.

Silica Crystalline Colloidal Array Deep Ultraviolet Narrow-Band Diffraction Devices

We developed a facile method to fabricate deep ultraviolet (UV) photonic crystal crystalline colloidal array (CCA) Bragg diffraction devices. The CCAs were prepared through the self-assembly of small, monodisperse, highly surface charged silica particles (~50 nm diameter) that were synthesized by using a modified Stöber process. The particle surfaces were charged by functionalizing them with the strong acid, non-UV absorbing silane coupling agent 3-(trihydroxylsilyl)-1-propane-sulfonic acid (THOPS). These highly charged, monodisperse silica particles self assemble into a face-centered cubic CCA that efficiently Bragg diffracts light in the deep UV. The diffracted wavelength was varied between 237 nm to 227 nm by tilting the CCA orientation relative to the incident beam between glancing angles from 90° to ~66°. Theoretical calculations predict that the silica CCA diffraction will have a full width at half-maximum (FWHM) of 2 nm with a transmission of ~10(-11) at the band center. We demonstrate the utility of this silica CCA filter to reject the Rayleigh scattering in 229 nm deep UV Raman measurements of highly scattering Teflon.

Reversible crosslinking density stimulated diffraction wavelength tuning of hydrogel-encapsulated crystalline colloidal arrays

The reversible variation in the observed stop band of a hydrogel-encapsulated crystalline colloidal array was achieved through the selective formation and destruction of –S–Pb–S– linkages within the hydrogel. A reversible 45nm stop band shift could be achieved with a cyclical treatment of Pb2+ and then dithiothreitol solution.

Responsive properties of crystalline colloidal arrays formed by core-shell microspheres with pH and temperature sensitivities

Polymeric microspheres responsive to pH and temperature changes have been prepared by a two-step surfactant-free emulsion polymerization with a polystyrene core and a hydrogel shell. The double sensitivity is achieved by the copolymerization in the shell layer of acrylic acid and N-isopropylacrylamide, which are pH- and thermo-responsive, respectively. Above a certain critical concentration, these microspheres are able to self-assemble into crystalline colloidal arrays, causing intense visible light diffraction. The behavior of these structures has been studied and correlated to the properties of the microspheres. The packing of these microspheres results in stimuli-sensitive colloidal crystals, with a behavior directly linked to the interactions between the particles and the surrounding media.

Understanding the thermo-sensitivity of crystalline colloidal arrays formed by poly(styrene-co-N-isopropylacrylamide) core–shell microspheres

Poly(styrene-co-N-isopropylacrylamide) core–shell microspheres have been synthesized by a two-step surfactant-free emulsion polymerization process. These microspheres are thermo-responsive with a clear volume phase transition around 30 °C and form crystalline colloidal arrays over a wide range of concentrations. The resulting crystalline arrays also display a response to temperature, visible through a change in the diffraction spectrum. However, the response appears to be highly dependent on the microsphere concentration. This behavior originates from a change in the short-range interactions between particles rather than from the volume change of the particles caused by the volume phase transition. Attractive van der Waals interactions increase while repulsions decrease; these changes only affect the equilibrium of concentrated samples, where the interparticle distance is sufficiently short to have an effect.

Photonic crystal pH and metal cation sensors based on poly(vinyl alcohol) hydrogel

A facile strategy for the preparation of poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAA) photonic crystal materials with pH and metal cation responses is presented. A solvent-assisted freeze–thaw method is used to form a physically cross-linked PVA gelated crystalline colloidal array (GCCA) photonic crystal. The PVA hydrogel-based photonic crystal sensors were prepared by the introduction of environmentally sensitive components responding to pH and cations into the GCCA system. The photonic crystal pH sensor shows good durability, a large stopband shift, and good adjustability. Further functionalization of 8-hydroxyquinoline makes the interpenetrating networks respond to metal cation concentrations which could be determined from the diffraction color change or precisely monitored by diffraction wavelength shifting using a spectrophotometer. The PVA hydrogel-based photonic crystal sensors could be fabricated in any size and geometry as needed because there is no requirement for a thin sample to allow for penetration of UV light and its processing time is greatly reduced compared with the use of colloidal crystal templates, which has an important significance in the large-scale industrial production in the future.

Dual signal glucose reporter based on inverse opal conducting hydrogel films

A novel glucose responsive hydrogel film possessing inverse opal structure and conducting property was developed, based on the principle of enzyme-catalytic redox reaction. The film can report glucose concentration via optical and electrochemical signals, respectively. To fabricate the sensor film, SiO2 crystalline colloidal array was utilized as a sacrificed template to endow the polyacrylamide(PAAm) hydrogel with non-closed-packed inverse opal structure, then conductive polymer (CP) poly(3,4-ethylenedioxythiophene) PEDOT was in situ chemically oxypolymerized to form interpenetrated network (IPN) within the hydrogel. The supporting matrix was activated by partial hydrolysis of amide groups on the backbone, to serve as bonding sites for glucose oxidase (GOx) and ion responsive elements. The changes in the hydrogel microenvironment caused by the catalytic product of glucose induced shrinkage of the hydrogel and a corresponding blue shift of the reflection peak of the film. Meanwhile, the hydrogel acted as a flexible amperometric electrode to sense current change. Linear response upon concentration of glucose ranged from 1 mM to 12 mM. Glucose was exhibited optically and electrically confirming a mutual regulation capacity to achieve better anti-interference performance.

Coupling of crystalline colloidal arrays with intrinsically conductive polymers: Reflection-type electrochromic devices

The attenuation of the reflected light from a polystyrene (PS) polymerized crystalline colloidal array (PCCA) is achieved through the electrochemical switching of the electrochromic material polyaniline-poly(2-acrylamido-2-methyl-1-propanesulfonicacid) (PANI-PAMPS). For this purpose, layered electrochromic devices (ECDs) were fabricated that employed a PS PCCA film, acting as both a reflecting substrate and polymeric electrolyte, and the conducting polymer PANI-PAMPS, which served as the electrochromic layer. The resulting ECDs exhibited the attenuation of reflectance peak at the stop band position of the PCCA with a 3% of reflectance contrast ratio.

Detection of bisphenol A using an opal photonic crystal sensor

A new opal photonic crystal sensor (OPCS) that allows the detection of label-free bisphenol A (BPA) is proposed in the current study. The concept of developing photonic-based sensors using combined photonic crystal technology and molecular imprinting techniques is introduced. First batches of the BPA-imprinted monodisperse PMMA spheres with a diameter of 220 (±5)nm were prepared based on the suspension polymerization, so numerous nanocavities derived from BPA imprinting were distributed in the PMMA spheres. The liquid monodisperse microspheres were made into a polymerized crystalline colloidal array (PCCA) opal photonic crystal sensor. The inherent high affinity of the nanocavities distributed in the sphere allows OPCS to recognize BPA specifically. The sensor is characterized by a 3D-ordered interconnected lattice structure. Between the monospheres, there are well-arranged pores allowing the target molecules to embed and transport. As a result, changes in diffraction intensity which are related to BPA concentrations can be observed with the sensor. The detection ranges of OPCS are at 1ng/ml–1μg/ml level. The new sensory system has high selectivity of the target molecules in their natural forms, is easy to use, and costs low. Overall, the proposed approach provides a versatile analytical system for the establishment of a new sensor for the detection of endocrine-disrupting chemicals.