Polystyrene Colloidal Crystals Research Articles

Lab-on-Device Synthesis of Hierarchical Macro/Mesoporous WO3 Semiconducting Films for High-Performance H2S Sensing.

The performance consistency of the gas sensor is strongly dependent on the interface binding between the sensitive materials and the electrodes. Traditional powder coating methods can inevitably lead to differences in terms of substrate-film interface interaction and device performance, affecting the stability and lifetime. Thus, efficient growth of sensitive materials on device substrates is crucial and essential to enhance the sensing performance, especially for stability. Herein, hierarchically ordered macro/mesoporous WO3 films are in situ synthesized on the electrode via a facile soft/hard dual-template strategy. Orderly arrayed uniform polystyrene (PS) microspheres with tailored size (ca. 1.2µm) are used as a hard template, and surfactant Pluronic F127 as a soft template can co-assemble with tungsten precursor into ordered mesostructure in the interstitials of PS colloidal crystal induced by solvent evaporation. Benefiting from its rich porosity and high stability, the macro/mesoporous WO3-based sensor shows high sensitivity (Rair/Rgas = 307), fast response/recovery speed (5/9 s), and excellent selectivity (SH2S/Smax > 7) toward 50ppm H2S gas (a biomarker for halitosis). Significantly, the sensors exhibit an extended service life with a negligible change in sensing performance within 60 days. This lab-on-device synthesis provides a platform method for constructing stable nanodevices with good consistency and high stability, which are highly desired for developing high-performance sensors.

Structural color modulation by laser post-processing on metal-coated colloidal crystals.

A method to use a pulsed solid-state laser to create structural color modulation on metal-coated colloidal crystal surfaces by changing the scanning speed has been proposed. Vivid colors as cyan, orange, yellow, and magenta are obtained with different predefined stringent geometrical and structural parameters. The effect of laser scanning speeds and polystyrene (PS) particle sizes on the optical properties is studied, and the angle-dependent property of the samples is also discussed. As a result, the reflectance peak is progressively red shifted along with increasing the scanning speed from 4mm/s to 200mm/s with 300nm PS microspheres. Moreover, the influence of the microsphere particle sizes and incident angle are also experimentally investigated. For 420 and 600nm PS colloidal crystals, along with a gradual decrease in the scanning speed of the laser pulse from 100mm/s to 10mm/s and an increase in the incident angle from 15° to 45°, there was a blue shift for two reflection peak positions. This research is a key, low-cost step toward applications in green printing, anti-counterfeiting, and other related fields.

Colloidal Photonic Crystal-Enhanced Fluorescence of Gold Nanoclusters: A Highly Sensitive Solid-state Fluorescent Probe for Creatinine.

Gold nanoclusters (AuNCs) are an intensely pursued class of fluorophores with excellent biocompatibility, high water solubility, and ease of further conjugation. However, their low quantum yield limits their applications, such as ultra-sensitive chemical or molecular sensing. To address this problem, various strategies have been adopted for augmenting their fluorescence intensity. Herein, we report a facile and scalable approach for the fluorescence enhancement of bovine serum albumin (BSA) capped AuNCs (BSA-AuNCs) using periodic, close-packed polystyrene colloidal photonic crystals (CPCs). The slow photon effect at the bandgap edges is utilized for the increased light-matter interactions and thereby enhancing the fluorescence intensity of the BSA-AuNCs. Compared to the planar polystyrene control sample, the CPC film yielded a 14-fold enhancement in fluorescence intensity. Further, we demonstrated the as-prepared BSA-AuNCs-CPC as a solid-state platform for the highly sensitive and selective fluorescence turn-off detection of creatinine at nanomolar level.

Size-dependent nanoscale soldering of polystyrene colloidal crystals by supercritical fluids

HypothesisPolymer particles self-assembled into colloidal crystals have exciting applications in photonics, phononics, templates for nanolithography, and coatings. Cold soldering utilizing polymer plasticization by supercritical fluids enables a novel, low-cost, low-effort, chemical-free means for uniform mechanical strengthening of fragile polymer colloidal crystals at moderate temperatures. Here, we aim to elucidate the role of particle size and gas-specific response for the most efficient soldering, exploring the full potential of this method. ExperimentsWe investigate the elastic properties of polystyrene colloidal crystals made of nanoparticles with different diameters (143 to 830 nm) upon treatment with supercritical Ar and He at room temperature. By employing Brillouin light scattering, we quantify the effect of nanoparticle size on the strengthening of interparticle contacts, evaluating the permanent change in the effective elastic modulus upon cold soldering. FindingsThe relative change in the effective elastic modulus reveals nonmonotonic dependence on the particle size with the most efficient soldering for mid-sized nanoparticles (about 610 nm diameter). We attribute this behavior to the crucial role of intrinsic fabrication impurities, which reduces the nanoparticles’ free surface exposed to plasticization by supercritical fluids. Supercritical Ar, a good solvent for polystyrene, enabled effective soldering of nanoparticles, whereas high-pressure He treatment is entirely reversible.

Novel WO3-PEDOT core–shell inverse opal films with enhanced electrochromic performance for smart windows

Electrochromic (EC) materials have been widely studied in energy-saving smart windows due to their reversible control of optical performance under electric fields. Novel tungsten oxide-poly (3, 4-ethylenedioxythiophene) (WO3-PEDOT) core–shell inverse opal (IO) films are obtained by electrochemical polymerization of PEDOT onto WO3 IO templates. The WO3 IO templates are prepared through the electrodeposition of WO3 into the voids of a polystyrene (PS) colloidal crystal, followed by calcination to remove the polystyrene microspheres. The designed microstructure and chemical composition of the WO3-PEDOT IO films are determined by SEM, XRD, XPS and Raman spectroscopy. The WO3-PEDOT IO films exhibit promising optical contrast ([Formula: see text]52% at 600 nm and [Formula: see text]77% at 1020 nm), indicating their bifunctional potentials in both visible and near infrared (NIR) region modulation. The WO3-PEDOT IO films also show excellent EC properties of much shorter response time (6.7 s for coloring and 5.8 s for bleaching) and superior cycling stability than that of the bare WO3 IO. These results suggest that the synergistic effect between the WO3 IO core and PEDOT shell may greatly increase the electrolyte accessibility to active sites and improve the interaction between the inorganic/organic interfaces to obtain enhanced EC performance.

Fabrication of three-dimensional ordered macroporous/mesoporous magnesium oxide for efficient cadmium removal

Cadmium (Cd) is a hazardous heavy metal, that poses a serious threat to human health. Magnesium oxide has shown excellent adsorption performance for the removal of Cd(II) from contaminated wastewater. Herein, three-dimensional ordered macroporous/mesoporous MgO (3DOM/m MgO) was synthesized by a double template method using amphiphilic triblock copolymer Pluronic F127 as the soft template and polystyrene colloidal crystal as the hard template. Compared with three-dimensional ordered macroporous MgO (3DOM MgO), 3DOM/m MgO exhibited a macro/mesoporous structure with a larger specific surface area (96.94 m2/g). The maximum adsorption capacity of 3DOM/m MgO reached 2933 mg/g for the removal of Cd(II) removal from an aqueous solution. BET and XPS analyses results revealed that the enhanced Cd(II) adsorption capacity of 3DOM/m MgO was attributed to its large specific surface area and the complexing ability of its hydroxy groups. The adsorption performance of 3DOM/m MgO was investigated by batch adsorption experiments, including adsorption isotherms and adsorption kinetics. 3DOM/m MgO completely removed 100 mg/L Cd(II), with a removal efficiency ≥99.9%. The adsorption behavior followed the pseudo-second-order kinetic model and Langmuir isotherm model, which revealed that the adsorption of Cd(II) on 3DOM/m MgO proceeded via homogeneous chemisorption. Due to its advantages of controllability and excellent adsorption performance, 3DOM/m MgO is a promising adsorbent for the removal of Cd(II) from polluted water.

Highly sensitive folic acid colorimetric sensor enabled by free-standing molecularly imprinted photonic hydrogels

Folic acid is an important biological compound for human disease diagnosis. Traditional detection methods of folic acid are mostly time-consuming or dependent on analytical equipment. Here we demonstrate the rapid and colorimetric detection of folic acid using a novel colorimetric sensor enabled by molecularly imprinted photonic hydrogels, which are prepared by the polymerization of precursor solution in the interstitial voids of the polystyrene colloidal crystal and subsequent removal of colloidal crystal and folic acid molecules. As folic acid is instable under the preparation process of molecularly imprinted photonic hydrogels, we introduce folic acid (imprinted molecule) in the form of supramolecular complex with β-CD units to improve its stability and further create stable molecular recognition sites. The folic acid recognition can be directly transferred into a visually perceptible color change due to the highly ordered macroporous structure. With this novel sensory system, the highly selective, high sensitive (as low as 10–12 M), and rapid response (< 60 s) to folic acid is achieved without the use of instruments. A novel folic acid colorimetric sensor enabled by molecularly imprinted photonic hydrogels is successfully prepared.

Mechanical reinforcement of polymer colloidal crystals by supercritical fluids

Colloidal crystals realized by self-assembled polymer nanoparticles have prominent attraction as a platform for various applications from assembling photonic and phononic crystals, acoustic metamaterials to coating applications. However, the fragility of these systems limits their application horizon. In this work the uniform mechanical reinforcement and tunability of 3D polystyrene colloidal crystals by means of cold soldering are reported. This structural strengthening is achieved by high pressure gas (N2 or Ar) plasticization at temperatures well below the glass transition. Brillouin light scattering is employed to monitor in-situ the mechanical vibrations of the crystal and thereby determine preferential pressure, temperature and time ranges for soldering, i.e. formation of physical bonding among the nanoparticles while maintaining the shape and translational order. This low-cost method is potentially useful for fabrication and tuning of durable devices including applications in photonics, phononics, acoustic metamaterials, optomechanics, surface coatings and nanolithography.

Effect of Nano-Carbon Addition on Angle Dependence of Polystyrene Colloidal Crystal Film

Low angle dependence single green polystyrene colloidal crystal films were prepared by vertical deposition method using polystyrene microspheres with size of 380 ± 10 nm as raw material and further modified by adding nano-carbon. Without nano-carbon addition, the film showed various colors with changing the angle of incident light under natural light. With nano-carbon addition, saturation and angle dependence of the polystyrene colloidal crystal film were remarkably improved. With 0.01 wt % nano-carbon addition, since the stray light of other wavelengths other than the band gap light was absorbed by the added nano-carbon, the film showed only green color under different angles of incident light, suggesting that the film had low angle dependence. It is significant in the research of color behavior and is helpful to obtain single color polystyrene colloidal crystal film.

Formation of ordered macroporous ZnFe2O4 anode materials for highly reversible lithium storage

In this paper, three-dimensionally ordered macroporous (3DOM) ZnFe2O4 (ZFO) was prepared via a templating method with polystyrene (PS) colloidal crystals, and used as highly reversible anode material for lithium ion batteries. In order to study influence of the macropore diameter on a cyclic behavior, 3DOM ZFO anode materials with two different macropore diameters of 160 and 55 nm were prepared. The 3DOM ZFO with a pore diameter of 160 nm (ZFO@160) delivered a high discharge capacity of ca. 1165.8 mAh g−1 at the initial cycle, as compared with those of 3DOM ZFO with 55 nm macropore (ZFO@55, ca. 1112.3 mAh g−1) and ZFO nanoparticles (ZFO NPs, ca. 925.6 mAh g−1). Moreover, a reversible capacity of 1143.7 mAh g−1 for the 3DOM ZFO@160 electrode was stably retained even after 100 cycles. The 3DOM ZFO@160 electrode also revealed much improved cycling performance, coulombic efficiency and rate capability, compared to the 3DOM ZFO@55 and ZFO NPs electrodes. These enhanced electrochemical properties could be ascribed to effective pore dimension with wide-spread channels, which could offer an efficient Li+ flux and a facile strain relaxation.

Real-time pressure monitoring system for microfluidic devices using deformable colloidal crystal membrane.

Understanding the hydrodynamic behavior in microfluidic devices is crucial for utilization of these systems in lab-on-a-chip applications. However, hydrodynamic capacitance in microfluidic devices causes a delay and mismatch between the applied pressure and actual pressure in the microchannel. Therefore, real-time monitoring of the site-specific internal pressure in microchannels is important for designing the operating conditions of the system. We introduce a deformable colloidal crystal membrane composed of polystyrene (PS) colloidal crystals and poly(dimethylsiloxane) (PDMS) and its integration into a PDMS microfluidic device. As pressure is applied to the device, the optical intensity reflected back from the colloidal crystal membrane changes due to membrane deformation. The optical signal originating from structural deformation of the colloidal crystal membrane allows the realization of a real-time pressure monitoring system, as no external apparatus or powering devices are required for signal processing. The internal pressure in microfluidic devices was also monitored to investigate the effect of the hydrodynamic capacitance during pressure application.

Synthesis of ordered macro-mesoporous Mg-Al composite oxides with high thermal stability and mechanical strength

Ordered macro-mesoporous Mg-Al composite oxides (denoted as OMM-MA-x) with tunable macropore size and highly homogenous distribution of Mg have been synthesized via a confined evaporation induced self-assembly method, in which triblock copolymer F127 and polystyrene colloidal crystals are utilized as templates for ordered mesoporous and macroporous structures, respectively. The resultant OMM-MA-x materials exhibit a much more ordered 2D hexagonal mesostructure constituting wall skeleton of ordered macropores and more excellent textural properties than those of ordered macro-mesoporous alumina materials. More importantly, both ordered mesostructure and macroporous structure of OMM-MA-x can be well maintained even after thermal treatment at 900 °C or pressure treatment at 15 MPa.

Fabrication and Characterization of Polystyrene Colloidal Photonic Crystals on Soft Sodium Alginate Film

Fabrication and Characterization of Polystyrene Colloidal Photonic Crystals on Soft Sodium Alginate Film

Laser damage resistance of polystyrene opal photonic crystals

The laser damage behavior of three-dimensional photonic crystals (3D-PCs) with an opal structure is investigated using both experimental and simulation methods. Polystyrene (PS) colloidal crystals films with a reflection peak at 1064 nm are used as the model material. Disordered films (DF) are fabricated with PS microspheres as contrast samples. The laser-induced damage threshold (LIDT) of 3D-PCs is tested, which is as 2.35 times high as the LIDT of DF. All laser damages are derived from defects in 3D-PCs, implying that the LIDT of ideal 3D-PCs will be significantly increased. The simulation results show that the electric field is contained in the pores of 3D-PCs while it is reduced in the PS microspheres, which may decrease the absorption of laser energy by 3D-PCs. In contrast, the electric field distribution is irregular in DF. Enhanced electric field areas are located in both the pores and microspheres of DF. Considering higher electric field intensity causes more energy absorption and higher temperature, the DF have a lower LIDT. The 3D-PCs structure uses ordered vacancy to contain and strike back laser energy and can increase the LIDT without changing the chemical composition of materials.

Unravelling the structural rearrangement of polymer colloidal crystals under dry sintering conditions.

The structural rearrangement of polystyrene colloidal crystals under dry sintering conditions has been revealed by in situ grazing incidence X-ray scattering. The measured diffraction patterns were analysed using distorted wave Born approximation (DWBA) theory and the structural parameters of the as-grown colloidal crystals of three different particle sizes were determined for the in-plane and out-of-plane directions in a film. By analysing the temperature evolution of the diffraction peak positions, integrated intensities, and widths, the detailed scenario of the structural rearrangement of crystalline domains at the nanoscale has been revealed, including thermal expansion, particle shape transformation and crystal amorphisation. Based on DWBA analysis, we demonstrate that in the process of dry sintering, the shape of colloidal particles in a crystal transforms from a sphere to a polyhedron. Our results deepen the understanding of the thermal annealing of polymer colloidal crystals as an efficient route for the design of new nano-materials.

Preparation of Humidity-Sensitive Poly(Ethylene Glycol) Inverse Opal Micropatterns Using Colloidal Lithography.

Humidity-sensitive poly(ethylene glycol) (PEG) inverse opals with micropatterns of 2 μm wide anti-swell-broken grooves were prepared using polystyrene (PS) colloidal crystals as templates and colloidal lithography. Monodisperse PS colloids were deposited in an ordered manner onto glass slides using a double-substrate vertical deposition method to form colloidal crystal templates. Poly(ethylene glycol) diacrylate (PEGDA) with photoinitiator was infiltrated into the interspaces of the colloidal crystals and photo-crosslinked by UV irradiation through a photomask. After removal the PS templates and unexposed PEGDA by tetrahydrofuran (THF), PEG hydrogel micropatterns with three-dimensional ordered porous structures were obtained. The band gaps of the PS colloidal crystals and corresponding PEG hydrogel inverse opals were measured by UV-VIS reflection spectrometer, calculated by Bragg law and simulated by Band SOLVE. The obtained PEG hydrogel inverse opal micropatterns can be used as sensors for humidity sensing due to absorption and desorption of moisture in the band gap structures. The sensor had a very reliable performance after repeated humidity sensing, and could be mass produced facilely with very low cost. The photopatterned anti-swell-broken grooves play an important role in the reliability of the sensors.

Fabrication of large-area, close-packed, monolayer colloidal crystals via a hybrid method of spin coating and peeling–draining

Large-area, close-packed, monolayer colloidal crystals can be used as templates in the preparation of micro/nano films. This work proposes a hybrid method of spin coating and peeling–draining for the production of large-area, close-packed, monolayer colloidal crystals. First, large-area monolayer polystyrene (PS) colloidal crystals were obtained through spin coating. Then, the colloidal crystal film was peeled from surface of the intermediate spin-coated silicon wafer and transferred to another substrate using a customized experimental device. Oxygen plasma treatment was utilized to modify the wettability of the silicon wafer, increase the uniformity of spin coating, and reduce the adhesion work of peeling. The key process parameters, such as the duration of oxygen plasma treatment, spin speed, peeling speed, and drop rate of water surface, of the proposed method were thoroughly analyzed and optimized. Three-inch, wafer-scale, large-area, close-packed monolayer colloidal crystals were obtained using the proposed method, which combines the advantages of spin coating and gas-liquid interface self-assembly and offers a stable and controllable approach to the fabrication of monolayer PS colloidal crystals.

Highly Sensitive Surface‐Enhanced Raman Scattering (SERS)‐ Based Multi Gas Sensor : Au Nanoparticles Decorated on Partially Embedded 2D Colloidal Crystals into Elastomer

AbstractAdvent of surface‐enhanced Raman spectroscopy (SERS) has engendered, the attention to exploit a facile, cost effective, 2D self‐assembly based architecture for sensing. Here, Au nanoparticles are decorated on controlled morphology of 2D polystyrene colloidal crystals (PSCCs), partially embedded into flexible polydimethylsiloxane elastomer. Self‐assembled flexible hexagonally close‐packed PSCCs form the 75 and 25 nm voids in the 500 and 200 nm, PSCCs monolayers and act as an effective plasmonic propagator for SERS sensors signal. Optical and sensing response investigates with UV‐Vis and Raman spectroscopy after the exposure of Au NP/2D PS CC/PDMS to NH3, H2O2, N2O and H2S gases environment. The increase in the SERS intensity at 491 cm−1 for the 200 nm, CCs based sensors as compared to 500 nm, indicates that the sensing response, strongly dependent on the CCs size. The red‐shift in the UV‐Vis spectra and enhancement in intensity of SERS designate that H2S forms the maximum Au NPs aggregates over the all tested gases. The chemisorptions on the phenyl ring, due to B2 symmetric modes of the PSCCs with orthogonal polarizability of Au NPs, act as a hot spot for higher sensing response for the detection of gaseous precursors with higher SERS sensitivity and reliability.

Synthesis of superhydrophobic polydopamine-Ag microbowl/nanoparticle array substrates for highly sensitive, durable and reproducible surface-enhanced Raman scattering detection

Surface-enhanced Raman scattering (SERS) sensor allows for fingerprinting and label-free molecular detection with a high sensitivity, but the simple fabrication of SERS active substrates with a well-control over the SERS performance, e.g. an ultra-high sensitivity, superior reproducibility and long-term stability remain a great challenge. Here, we introduce an easy strategy for synthesizing polydopamine-Ag microbowl/nanoparticle array (PDA-Ag MNA) substrates with a tunable superhydrophobic surface, applicable for ultra-highly sensitive SERS detection. First, the periodically dented PDA films are prepared by polymerizing dopamine onto 2D polystyrene colloidal crystals formed at the liquid/air interface, and followed with an in-situ reduction of Ag ions to Ag nanoparticles after removing polystyrene. The surface morphology, i.e. microbowl/nanoparticle structure, is well-controlled, therefore, allowing that the SERS activity of the substrate is under control. Inspired by the superhydrophobic hierarchical surface of the rose petals, this analogous MNA surface is subsequently endowed to be superhydrophobic. This way, the SERS detection of ultra-dilute solute (10−14M) can be achieved by concentrating analytes within a localized region. Moreover, this substrate also shows a superior reproducibility in result and durability in use. This strategy exhibits a realistic paradigm for further improving the sensitivity of the SERS technique.

3D investigation on polystyrene colloidal crystals by floatage self-assembly with mixed solvent via synchrotron radiation x-ray phase-contrast computed tomography

The floatage self-assembly method was introduced with mixed solvent as the medium of polystyrene sphere suspension to fabricate the colloidal crystal. The three dimensional (3D) void system of the colloidal crystal was noninvasively characterized by synchrotron radiation phase-contrast computed tomography, and the quantitative image analysis was implemented aiming to the polystyrene sphere colloidal crystal. Comparing with gravity sedimentation method, the three samples fabricated from floatage self-assembly with mixed solvents have the lowest porosity, and when ethylene glycol and water were mixed with ratio of 1:1, the lowest porosity of 27.49% could be achieved, that has been very close to the minimum porosity of ordered 3D monodisperse sphere array (26%). In single slices, the porosities and fractal dimension for the voids were calculated. The results showed that two factors would significantly influence the porosity of the whole colloidal crystal: the first deposited sphere layer's orderliness and the sedimentation speed of the spheres. The floatage self-assembly could induce a stable close-packing process, resulted from the powerful nucleation force-lateral capillary force coupled with the mixed solvent to regulate the floating upward speed for purpose of matching the assembly rate.