Colloidal Arrays Research Articles

Preparation of free-standing two-dimensional colloidal crystal arrays

A simple method was developed to prepare ultra-thin, large-area, free-standing two-dimensional (2D) polymethylmethacrylate (PMMA) colloidal crystal array monolayers by assembling PMMA colloids suspended in toluene on water surface. Diffraction of the free-standing films could be adjusted through the particle size or operation time.

Diffusion process of an ink drop in core–shell silica–titania pigment particles

Recording coatings have been successfully prepared by the core–shell structural silica–titanium dioxide particles, which were synthesized using sol–gel methods and fabricated as a close-packed colloidal crystalline array. The size of the nano-silica particles (50–100nm) was controlled via varying the concentration of ammonium hydroxide. The silica spheres coated with titania (core–shell structure) were prepared by a self-assembly coating deposition process. Transmission electron microscopy and scanning electron microscopy were used to analyze the microstructure of the core/shell composite particles. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to analyze the molecular structure of the composite particles and the formation of the chemical bonds (Ti–O and Ti–O–Si) on the shell surface. The prepared composite pigment particles were applied in recording materials. The diffusion process of the ink drop on the surface of the recording materials was studied by the edge detection method. We also investigated the role of the ink drop in the diffusion process of the different composite pigment particle.

Frontispiece: Thermally Tunable Hydrogels Displaying Angle‐Independent Structural Colors

Angle-Independent Structural Color In their Communication on page 15368 ff., Y. Takeoka et al. report on thermally tunable hydrogels displaying angle-independent structural colors that were prepared from colloidal amorphous array templates and carbon black.

Thermosensitive soft glassy colloidal arrays of block-copolymer-grafted silica nanoparticles in an ionic liquid

A short-range-ordered, soft glassy colloidal array (SGCA) exhibits angle-independent and non-iridescent structural color. To control the angle-independent structural color by external stimuli, a thermosensitive SGCA composed of block copolymer (poly(benzyl methacrylate)-block-poly(methyl methacrylate), PBnMA-b-PMMA) grafted silica nanoparticles was prepared in an ionic liquid. The glassy arrays showed a blue shift of reflection peak at semidilute particle concentrations, but an opposite red shift at high particle concentrations with increasing temperature.

Synthesis of Rh/Macro-Porous Alumina Over Micro-Channel Plate and Its Catalytic Activity Tests for Diesel Reforming

Macro-porous Al2O3 as the catalytic support material was synthesized using colloidal polystyrene spheres over a micro-channel plate. The colloidal polystyrene spheres were used as a template for the production of an ordered macro porous material using an alumina nitrate solution as the precursor for Al2O3. The close-packed colloidal crystal array template method was applied to the formulation of ordered macro-porous Al2O3 used as a catalytic support material over a micro-channel plate. The solvent in the mixture solution, which also contained the colloidal polystyrene solution, aluminum nitrate solution and the precursor of the catalytic active materials (Rh), was evaporated in a vacuum oven at 50 degrees C. The ordered polystyrene spheres and aluminum salt of the solid state were deposited over a micro channel plate, and macro-porous Al2O3 was formed after calcination at 600 degrees C to remove the polystyrene spheres. The catalytic activity of the Rh/macro-porous alumina supported over the micro-channel plate was tested for diesel reforming.

Thermally Tunable Hydrogels Displaying Angle‐Independent Structural Colors

AbstractWe report the preparation of thermally tunable hydrogels displaying angle‐independent structural colors. The porous structures were formed with short‐range order using colloidal amorphous array templates and a small amount of carbon black (CB). The resultant porous hydrogels prepared using colloidal amorphous arrays without CB appeared white, whereas the hydrogels with CB revealed bright structural colors. The brightly colored hydrogels rapidly changed hues in a reversible manner, and the hues varied widely depending on the water temperature. Moreover, the structural colors were angle‐independent under diffusive lighting because of the isotropic nanostructure generated from the colloidal amorphous arrays.

Thermally Tunable Hydrogels Displaying Angle-Independent Structural Colors.

We report the preparation of thermally tunable hydrogels displaying angle‐independent structural colors. The porous structures were formed with short‐range order using colloidal amorphous array templates and a small amount of carbon black (CB). The resultant porous hydrogels prepared using colloidal amorphous arrays without CB appeared white, whereas the hydrogels with CB revealed bright structural colors. The brightly colored hydrogels rapidly changed hues in a reversible manner, and the hues varied widely depending on the water temperature. Moreover, the structural colors were angle‐independent under diffusive lighting because of the isotropic nanostructure generated from the colloidal amorphous arrays.

Polarized SERS on linear arrays of silver half-shells: SERS re-radiation modulated by local density of optical states

This work investigates polarization effects in surface-enhanced Raman scattering (SERS) on a particular kind of hybrid colloidal plasmonic-photonic crystal consisting in linear arrays of polystyrene colloids coated by a silver film forming caps (half-shells). The polarization of Raman scattering of adsorbed molecules is found to be imposed by the linear morphology of the plasmonic nanostructures, independent of the incident polarization. Specifically, it is demonstrated that the electric field component parallel to the linear plasmonic nanostructures brings the main contribution to the SERS enhancement for both parallel and perpendicular excitation. The stronger plasmon resonance, polarized along the chain of metal half-shells, is the one that determines the polarization of the SERS scattering, even if this resonance is not directly excited by the incident laser, but only re-radiated photons couple to it. The observed dependences indicate a strong contribution of the second part of the E4 enhancement, related to the enhancement at the frequency of the Raman scattered photons. FDTD electromagnetic simulations, taking into account both the excitation enhancement at the location of the scatterer and the enhancement of the scattering (re-radiation) by local density of optical states (LDOS) effects, support the experimental results. The presented results emphasize the practical importance of knowing and controlling the excitation/detection conditions in SERS experiments with nanostructures possessing well-defined and oriented morphological features. The LDOS approach employed here for the theoretical analysis, despite not being common for this purpose, proves its potential for becoming a useful ingredient in the analysis of plasmon-enhanced spectroscopies.

Selective p- and n-Doping of Colloidal PbSe Nanowires To Construct Electronic and Optoelectronic Devices.

We report the controlled and selective doping of colloidal PbSe nanowire arrays to define pn junctions for electronic and optoelectronic applications. The nanowires are remotely doped through their surface, p-type by exposure to oxygen and n-type by introducing a stoichiometric imbalance in favor of excess lead. By employing a patternable poly(methyl)methacrylate blocking layer, we define pn junctions in the nanowires along their length. We demonstrate integrated complementary metal-oxide semiconductor inverters in axially doped nanowires that have gains of 15 and a near full signal swing. We also show that these pn junction PbSe nanowire arrays form fast switching photodiodes with photocurrents that can be optimized in a gated-diode structure. Doping of the colloidal nanowires is compatible with device fabrication on flexible plastic substrates, promising a low-cost, solution-based route to high-performance nanowire devices.

Measuring Ligand-Dependent Transport in Nanopatterned PbS Colloidal Quantum Dot Arrays Using Charge Sensing.

Colloidal quantum dot arrays with long organic ligands have better packing order than those with short ligands but are highly resistive, making low-bias conductance measurements impossible with conventional two-probe techniques. We use an integrated charge sensor to study transport in weakly coupled arrays in the low-bias regime, and we nanopattern the arrays to minimize packing disorder. We present the temperature and field dependence of the resistance for nanopatterned oleic-acid and n-butylamine-capped PbS arrays, measuring resistances as high as 10(18) Ω. We find that the conduction mechanism changes from nearest neighbor hopping in oleic-acid-capped PbS dots to Mott's variable range hopping in n-butylamine capped PbS dots. Our results can be understood in terms of a change in the interdot coupling strength or a change in density of trap states and highlight the importance of the capping ligand on charge transport through colloidal quantum dot arrays.

Cellulose photonic crystal film sensor for alcohols

A novel photonic crystal sensor, a cellulose film with a three dimensional (3D) colloidal array embedded inside, was fabricated by infiltrating the voids of a 3D poly methyl methacrylate (PMMA) colloidal array with methyl cellulose aqueous solution, followed by thermal curing. When the obtained cellulose photonic crystal film sensor (CPCFS) was immersed in alcohols, including ethanol, n-propanol, isopropanol and n-butanol, its lattice constant and mean effective refractive index increased, which led to the redshift of the reflection of incident light. The redshift of this sensor had linear response to the concentration of alcohol vapors, while its structural color changed from blue to green visually. This CPCFS demonstrates promising potential as an on-site monitoring sensor for alcohols and an inexpensive and minimally invasive breathalyzer in the future.

Wearable red-green-blue quantum dot light-emitting diode array using high-resolution intaglio transfer printing.

Deformable full-colour light-emitting diodes with ultrafine pixels are essential for wearable electronics, which requires the conformal integration on curvilinear surface as well as retina-like high-definition displays. However, there are remaining challenges in terms of polychromatic configuration, electroluminescence efficiency and/or multidirectional deformability. Here we present ultra-thin, wearable colloidal quantum dot light-emitting diode arrays utilizing the intaglio transfer printing technique, which allows the alignment of red–green–blue pixels with high resolutions up to 2,460 pixels per inch. This technique is readily scalable and adaptable for low-voltage-driven pixelated white quantum dot light-emitting diodes and electronic tattoos, showing the best electroluminescence performance (14,000 cd m−2 at 7 V) among the wearable light-emitting diodes reported up to date. The device performance is stable on flat, curved and convoluted surfaces under mechanical deformations such as bending, crumpling and wrinkling. These deformable device arrays highlight new possibilities for integrating high-definition full-colour displays in wearable electronics.

Two-color beam improvement of the colloidal particle lens array assisted surface nanostructuring

We consider laser nanostructuring of the material surface by means of a colloidal particle lens array. Here, the monolayer of dielectric micro- or nanospheres placed on the surface acts as an array of near-field lenses that focus the laser radiation into the multitude of distinct spots, allowing the formation of many structures in a single stage. We show that conversion of a small part of the energy of the femtosecond beam into the second harmonic (SH) is an efficient way to increase the surface density of obtained nanostructures. By combining the fundamental frequency and the SH, one benefits both from the power of the former and from the focusing ability of the latter. This combination provides an efficient nanostructuring with sphere diameter close to the wavelength of the second harmonic. The possibility to create arrays of nanostructures with surface density above 5×108 cm−2 with femtosecond Ti:sapphire laser operating at 800 nm was demonstrated by employing 0.45 μm spheres.

A composite hydrogels-based photonic crystal multi-sensor

A facile route to prepare stimuli-sensitive poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) gelated crystalline colloidal array photonic crystal material was developed. PVA was physically gelated by utilizing an ethanol-assisted method, the resulting hydrogel/crystal composite film was then functionalized with PAA to form an interpenetrating hydrogel film. This sensor film is able to efficiently diffract the visible light and rapidly respond to various environmental stimuli such as solvent, pH and strain, and the accompanying structural color shift can be repeatedly changed and easily distinguished by naked eye.

Optically diffracting hydrogels for screening kinase activity in vitro and in cell lysate: impact of material and solution properties.

Optically diffracting films based on hydrogel-encapsulated crystalline colloidal arrays have considerable utility as sensors for detecting enzymaticphosphorylation and, thus, in screening small molecule modulators of kinases. In this work, we have investigated the impact of hydrogel properties, as well as the role of the ionic character of the surrounding environment, on the optical sensitivity of kinase responsive crystalline colloidal array-containing hydrogels. In agreement with a model of hydrogel swelling, the optical sensitivity of such materials increased as the shear modulus and the Flory-Huggins interaction parameter between polymer and solvent decreased. Additionally, elimination of extraneous charges in the polymer backbone by exploiting azide-alkyne click chemistry to functionalize the hydrogels with a peptide substrate for protein kinase A further enhanced the sensitivity of the optically diffracting films. Increasing peptide concentration and, in turn, immobilized charge within the hydrogel network was shown to increase the optical response over a range of ionic strength conditions. Ultimately, we showed that, by tuning the hydrogel and solution properties, as little as 0.1 U/μL protein kinase A could be detected in short reaction times (i.e., 2 h), which is comparable to conventional biochemical kinase assays. We further showed that this approach can be used to detect protein kinase A activity in lysate from HEK293 cells. The sensitivity of the resulting films, coupled with the advantages of photonic crystal based sensors (e.g., label free detection), makes this approach highly attractive for screening enzymatic phosphorylation.

Fabrication of a platform to isolate the influences of surface nanotopography from chemistry on bacterial attachment and growth.

Billions of dollars are spent annually worldwide to combat the adverse effects of bacterial attachment and biofilm formation in industries as varied as maritime, food, and health. While advances in the fabrication of antifouling surfaces have been reported recently, a number of the essential aspects responsible for the formation of biofilms remain unresolved, including the important initial stages of bacterial attachment to a substrate surface. The reduction of bacterial attachment to surfaces is a key concept in the prevention or minimization of biofilm formation. The chemical and physical characteristics of both the substrate and bacteria are important in understanding the attachment process, but substrate modification is likely the most practical route to enable the extent of bacterial attachment taking place to be effectively controlled. The microtopography and chemistry of the surface are known to influence bacterial attachment. The role of surface chemistry versus nanotopography and their interplay, however, remain unclear. Most methods used for imparting nanotopographical patterns onto a surface also induce changes in the surface chemistry and vice versa. In this study, the authors combine colloidal lithography and plasma polymerization to fabricate homogeneous, reproducible, and periodic nanotopographies with a controllable surface chemistry. The attachment of Escherichia coli bacteria onto carboxyl (plasma polymerized acrylic acid, ppAAc) and hydrocarbon (plasma polymerized octadiene, ppOct) rich plasma polymer films on either flat or colloidal array surfaces revealed that the surface chemistry plays a critical role in bacterial attachment, whereas the effect of surface nanotopography on the bacterial attachment appears to be more difficult to define. This platform represents a promising approach to allow a greater understanding of the role that surface chemistry and nanotopography play on bacterial attachment and the subsequent biofouling of the surface.

Self-Assembly of Colloidal Nanorods Arrays

Recently, self-assembly of colloidal semiconductor nanocrystals (NCs) have attracted a great interest due to their flexible synthesis with tunable band gaps and shape-dependent optical and electronic properties. In particular, nanorods (NRs) superlattice is receiving considerable attention. Typically, the NRs superlattice is prepared by guiding the process of self-assembly through external forces. In this article, recent development of self-assembly approaches at work in fabricating NRs superlattices was reviewed. Despite those effective self-assembly techniques through external controls to obtain NCs assemblies during deposition were widespread used. But these techniques are time consuming, and cannot get rid of the organic capping insulated molecules surrounding the NCs. So there is still a challenge to guarantee the electron/hole dissociation as well as the charge transport of NCs. Here, thermal annealing method that applies selectivity even in the presence of organic molecules will be adopted to obtain colloidal NRs superlattices, and the self-assembly mechanism of NRs were briefly addressed.

Study on a Photonic Crystal Hydrogel Material for Chemical Sensing

There is intense interest in the applications of photonic crystal hydrogel materials for the detection of glucose, metal ions, organophosphates and so on. In this paper, monodisperse polystyrene spheres with diameters between 100 ~ 440 nm were synthesized by emulsion polymerization. Highly charged polystyrene spheres readily self-assembled into crystalline colloidal array because of electrostatic interactions. Photonic crystal hydrogel materials were formed by polymerization of acrylamide hydrogel around the crystalline colloidal arrays of polystyrene spheres. After chemical modification of hydrogel backbone with carboxyl groups, our photonic crystals hydrogel materials are demonstrated to be excellent in response to pH and ionic strength changes.

2-Allylhexafluoroisopropanol Treated Photonic Crystal Material for DMMP Detection

Some photonic crystal materials are developed as chemical detection materials. Varies of sensitive chemical group can be used for varies of chemical detection. In this paper, Polystyrene particles in 240 nm size were prepared firstly. The polystyrene particles were self-assembled into crystalline colloidal arrays. A kind of fluoride-bearing chemical, 2-Allylhexafluoroisopropanol, were induced to the Polystyrene crystalline colloidal arrays. Then the diffraction properties were test. After treated by 2-Allylhexafluoroisopropanol, the Polystyrene crystalline colloidal arrays get a change of diffraction in both the wavelength and the intensity. When exposed to saturated vapor of DMMP.

Preparation and upconversion emission modification of crystalline colloidal arrays and rare earth fluoride microcrystal composites.

In this paper, highly ordered crystalline colloidal arrays containing rare earth fluoride microcrystals were fabricated. The upconversion emission property of rare earth fluoride microcrystals in crystalline colloidal arrays was studied and modified. A significant suppression and enhancement of the upconversion emission from the rare earth fluorides can be observed in the regions of the photonic band gap and its band edge, respectively. The suppression or enhancement factor was shown to be related to the ordered degree of the crystalline colloidal arrays and is critical in the preparation of upconversion displays and low-threshold lasers.