Colloidal Microspheres Research Articles

Partially bio-derived phosphazene-tannic acid microspheres as fire retardant additives for an epoxy tannic acid resin system

In this work, partially bio-derived colloidal microspheres are synthesised from tannic acid (TA) and hexachloro-cyclophosphazene (HCCP), then investigated for their effectiveness as a fire-retardant additive to a partially bioderived epoxy resin system. The epoxy resin system is based upon diglycidyl ether of bisphenol A (DGEBA) and tannic acid (TA), a bio-derived highly aromatic phenolic curative noted for its inherent fire retardancy. This study presents the impact of increasing the concentration of the phosphazene-TA microspheres (TAPZ) and varying the DGEBA-TA stoichiometry to determine the optimum formulation required to achieve the greatest improvement in fire retardancy. At 15 wt% TAPZ addition, the DGEBA-TA resin system easily achieves a V-0 rating according to the UL-94 vertical burn test, measures 29 % for the limiting oxygen value (LOI) and displays a 62 % reduction in peak heat release rate (PHRR) compared with the unmodified DGEBA-TA network. TAPZ addition however reduces the glass transition temperature (Tg) from 187 °C to 155 °C, flexural strength by up to 30 % and increases viscosity significantly. Varying the stoichiometry between DGEBA and TA shows that additional surface hydroxyl groups from the TAPZ microspheres accelerate the DGEBA-TA reaction through enhancing interfacial reaction between residual epoxide groups of the cured epoxy network. Overall, these results present a promising approach to the development of a highly fire retardant, high performance, and highly bio-derived epoxy network and composite.

Carbon dot-loaded Fe3O4 as photonic pigments for multilevel anti-counterfeiting

Amorphous arrays assembled from colloidal microspheres are a way that obtains angle-independent structural colors. In order to obtain additional properties, colloidal microspheres, which are constituent units, can be modified with other materials. Here, we utilized the silane-functionalized carbon quantum dots (SiCDs) by incorporating them into the Stöber reaction to fabricate Fe3O4@SiO2/SiCDs nanospheres with a core-shell structure. Amorphous colloidal arrays (ACAs) were constructed on commercial printing paper using Fe3O4@SiO2/SiCDs nanoparticles as structural units by a simple permeation assembly. Macroscopically, the prepared ACAs exhibit the magnetic properties of Fe3O4, while under sunlight, they display bright, angle-independent structural colors. Under ultraviolet light, the array shows significant fluorescence. This enables the presentation of multidimensional information under varying magnetic and lighting conditions. By adjusting the thickness of the outer SiO2/SiCDs composite layer, the optical properties and magnetism can be controlled easily. Moreover, due to the strong light absorption capability and high refractive index of Fe3O4, the digital patterns constructed with Fe3O4@SiO2/SiCDs nanospheres demonstrate excellent multi-level anti-counterfeiting characteristics, even under water exposure. The magnetic properties of Fe3O4@SiO2/SiCDs nanospheres, along with their distinct display characteristics under different optical environments, suggest their wide applicability in the fields of multifunctional anti-counterfeiting pigments, bioimaging, and sensing displays.

Radiosynovectomy for hemophilic arthropathies. Analysis of opportunities and prospects

Introduction. A characteristic symptom of hemophilia is joint hemorrhage (hemarthroses).Aim: to evaluate the possibilities of radiosynovectomy in hemophilic arthropathies.Main findings. Radiosynovectomy (RSE) or radiosynoviorthesis (RSO) is a technique that achieves a long-lasting effect in chronic synovitis and hemophilic arthropathy. It consists of intra-articular injection of radiopharmaceuticals (RFLP) in the form of colloidal solutions, macroaggregates or microspheres containing radioactive isotopes, which are rapidly phagocytized by the covering cells of the synovial membrane. After such capture, the synovial sheath is subjected to intensive “internal” irradiation, which results in superficial fibrosis of synovial tissue and persistent suppression of joint inflammation.

Plasmonic structurally colored surfaces with metal film over microsphere lattices

Structural coloring through plasmonic nanostructures involves the manipulation of light interaction with nanostructured metallic surfaces to selectively reflect specific spectral ranges within the visible spectrum. Unlike conventional pigments that absorb light based on their chemical properties, plasmonic nanostructures achieve color through their physical configuration. This study investigates the potential of generating plasmonic structural colors by utilizing self-assembled colloidal microsphere lattices that are coated with thin metal films. Finite-Difference Time-Domain (FDTD) simulations are employed on realistic models to analyze the optical reflectance of dielectric microsphere lattices ranging in sizes from 300 to 700 nm, coated with varying thicknesses (20–200 nm) of different metals (Al, Ag, Au). The reflectance spectra are then translated into specific colors using a software algorithm, with the color representations plotted on CIE1931 diagrams. Furthermore, to validate the theoretical findings, two-dimensional polystyrene microsphere arrays coated with Au and Ag films are prepared, and their reflectance spectra and color images are examined. The resulting plasmonic colors can be adjusted by altering the sphere size, the type of metal used, and the thickness of the coating, demonstrating their potential for diverse color-based applications.

Rapid Construction of PVA@CDs/SiO2 Fluorescent/Structural Color Dual-Mode Anti-Counterfeiting Labels via Spray-Coating Method.

A method of sequential spraying of polyvinyl alcohol with carbon quantum dots (PVA@CDs) aqueous suspension and SiO2 aqueous suspension is proposed to rapidly prepare multicolor dual-mode anti-counterfeiting labels. With the optimization of the concentration (15%) of colloidal microspheres in the SiO2 aqueous suspension as well as the spraying process parameters (spray distance of 10 cm, spray duration of 3 s, and assembly temperature of 20 °C), different-sized SiO2 microspheres (168 nm, 228 nm, and 263 nm) were utilized to rapidly assemble red, green, and blue photonic crystals. Furthermore, the tunable fluorescence emission of carbon quantum dots endows the labels with yellow, green, and blue fluorescence. The constructed dual-mode labeling was used to develop an anti-counterfeiting code with dual-channel information storage capabilities and also to create dual-mode multicolor anti-counterfeiting labels on various packaging substrates. This work provides a novel solution for anti-counterfeiting packaging and information storage.

Atomization deposition fabricating angle-independent structural colored fabrics with outstanding stability, hydrophobicity, flexibility and breathability

Structural colored fabrics based on colloidal photonic crystals (CPCs) have attracted increasing concerns benefitting from the fadeless and environmental-friendly properties, which might promote the revolution of traditional textile printing and dyeing industry. However, enhancing the structural stability of CPCs on fabrics in a high efficiency and easy-to-perform manner still remains challenges. Here, we constructed novel brilliant angle-independent structural colored fabrics through atomization deposition fabricating poly(hexafluorobutyl acrylate-co-glycidyl methacrylate) (poly(HFBA-co-GMA)) CPCs on polyester (PET) fabrics. On the one hand, the hexafluorobutyl groups on poly(HFBA-co-GMA) colloidal microspheres endow the fabrics with excellent hydrophobicity. On the other hand, the hexafluorobutyl groups are able to generate strong hydrogen bonding interactions with carboxyl groups on PET fabrics, providing the structural colored fabrics with outstanding structural stability. Moreover, excellent flexibility, outstanding breathability, patterning and large-scale production of structural colored fabrics were also realized. This work offers a brand-new fashion towards manufacturing high performance structural colored fabrics, which might hold the potential in industrial eco-friendly coloration technology.

Composite photonic microobjects with anisotropic photonic properties from a controlled wet etching approach

Colloidal photonic microobjects with anisotropic properties find diverse applications, from building blocks of tunable displays to miniaturized optoelectronic devices. Microfluidics is a robust platform for the construction of colloidal photonic microobjects. Generally, creating colloidal photonic microobjects with Janus structures via microfluidics involves either injecting different colloidal photonic streams to form Janus photonic microbjects or applying a selective coating of a metallic layer to one side of the as-prepared photonic microobjects. However, those approaches either are time-consuming or may pose negative impact on the photonic properties of the photonic microobjects. In this report, we introduce a facile yet highly reproducible approach to fabricate photonic microobjects with Janus photonic property. To achieve this, colloidal photonic microspheres that are composed of a photonic resin dispersion of single-sized SiO2 nanoparticles (NPs) are prepared via a single emulsion-based microfluidics. Subsequently, one hemisphere of each microsphere is embedded into a polystyrene (PS) film, serving as a protection matrix. The microspheres embedded PS film is overturned and placed in a controlled amount of HF solution to etch the SiO2 NPs in the unprotected domain, yielding Janus photonic microobjects. The ratio of opal to inverse-opal structure on the surface of the photonic microobjects can be accurately controlled by playing the etching parameters. The porous structure of the etched part of the microobjects can be further functionalized by polymer infiltration, featuring the microobjects with fluorescence property. These multifunctionalized microobjects may find potential applications in the fields of advanced pigments, anticounterfeiting materials, etc. This strategy paves a facile way for the design and construction other miniaturized devices.

Linking local microstructure to fracture location in a two-dimensional amorphous solid under isotropic strain.

Brittle fracturing of materials is common in natural and industrial processes over a variety of length scales. Knowledge of individual particle dynamics is vital to obtain deeper insight into the atomistic processes governing crack propagation in such materials, yet it is challenging to obtain these details in experiments. We propose an experimental approach where isotropic dilational strain is applied to a densely packed monolayer of attractive colloidal microspheres, resulting in fracture. Using brightfield microscopy and particle tracking, we examine the microstructural evolution of the monolayer during fracturing. Furthermore, we propose and test a parameter termed Weakness that estimates the likelihood for particles to be on a crack line, based on a quantified representation of the microstructure in combination with a machine learning algorithm. Regions that are more prone to fracture exhibit an increased Weakness value, however the exact location of a crack depends on the nucleation site, which cannot be predicted a priori. An analysis of the microstructural features that most contribute to increased Weakness values suggests that local density is more important than orientational order. Our methodology and results provide a basis for further research on microscopic processes during the fracturing process.

Rotational diffusion of colloidal microspheres near flat walls.

Recently, colloids with an off-center fluorescent core and homogeneous composition have been developed to measure the rotational diffusivity of microparticles using 3D confocal microscopy in refractive index-matched suspensions. Here, we show that the same particles may be imaged using a standard fluorescence microscope to yield their rotational diffusion coefficients. Trajectories of the off-center core may be combined with known expressions for the correlation decay of particle orientations to determine an effective rotational diffusivity. For sedimented particles, we also find the rotational diffusivity about axes perpendicular and parallel to the interface by adding some bright field illumination and simultaneously tracking both the core and the particle. Trajectories for particles of different sizes yield excellent agreement with hydrodynamic models of rotational diffusion near flat walls, taking the sedimentation-diffusion equilibrium into account. Finally, we explore the rotational diffusivity of particles in crowded two-dimensional monolayers, finding a different reduction of the rotational motion about the two axes depending on the colloidal microstructure.

Preparation and formation mechanism of colorful photonic crystals on rough yarns

The environmentally friendly dyeing of textiles combining regular photonic crystals (PCs) has shown remarkable promise for application. However, the surface is rough and undulating and contains many harnesses due to full-curved structure of yarns. All these factors increase the difficulty of assembling colloidal microspheres into regular PCs on yarns. Therefore, relevant studies on the preparation methods and fundamental theories for constructing bionic structural colors on conventional flexible yarns are few. This study contains two main parts: first, regular PC-based yarns were produced by the dip coating method with poly (styrene–butyl acrylate–methacrylate) (P(St–BA–MAA)) as building block. Specifically, the softness and surface flatness of acrylic yarns were improved using silicone-modified polymer solution and cationic acrylate solution. The results indicated that assembling of PC with vivid structural color was easier when the base color of yarns was black and the concentration of P(St–BA–MAA) colloidal microspheres was about 60 wt%. Second, the self-assembling mechanism of microspheres on acrylic yarns was further studied by untwisting and slicing. The results showed that colloidal microspheres would fill the surfaces and voids of the outer fibers of acrylic yarns to form regular PCs, and they would also enter the inner fibers of yarns by capillary forces. However, the structure of yarns was tight inside and loose outside due to twisting and other reasons. Therefore, the colloidal microspheres had more difficulty entering the fibers on the inner side of the yarn to form an ordered PC structure when the fibers were closer to the yarn axis. The PC-based colored yarn also remained bright after the rubbing test. The color phase of the structured colored yarns based on PC could be adjusted as well by regulating the particle size and the observation angle. The prepared structured colored yarns were woven into fabrics, which were named yarn-structure colored fabrics. This research provides theoretical support and technical guidance for the preparation and practical application of flexible structured colored yarns based on PC.

Photonic Crystal Sensor Evaluating the Effectiveness of Medical Products under Different Storage Conditions.

The effectiveness of time- and temperature-sensitive medical products (TTSMPs) (vaccines, medicines, and biological agents) is generally evaluated by sporadically checking the storage conditions recorded in electronic thermometers. However, electronic thermometers do not achieve all-time and all-regional record, resulting in the wrong evaluation of a single TTSMP and seriously endangering public health. Herein, we report a photonic crystal sensor for evaluating the effectiveness of a single TTSMP processing storage environment. The photonic crystal sensor assembled by colloidal microspheres (WO3-x nanospheres were added into the microsphere gap) generates a fascinating composite color of angle-dependent structural color (maximum reflectivity = 45%) and durative color (WO3-x coloration). Effectiveness evaluation principle reveals that the pattern on the sensor, which was printed by the composite color, fades sensitively to time and temperature, thus having different visible periods (0-21 days affected by temperature). The visible periods of the patterns can be used to evaluate a single TTSMP's effectiveness stored under different temperatures. Furthermore, the photonic crystal sensor shows outstanding flexibility and slight adhesion, offering a promising application toward the effectiveness evaluation of TTSMPs throughout storage, transportation, and sales processes.

Hazardous Gases-Responsive Photonic Crystals Cryogenic Sensors Based on Antifreezing and Water Retention Hydrogels.

Nowadays, the sensing of hazardous gases is urgent for the consideration of public safety and human health, especially in extreme conditions of low temperatures. In this study, a photonic crystals (PhCs) sensor with water retention and antifreezing properties was developed and applied to visual hazardous gases sensing at low temperature, passively. The sensor was prepared by dip-coating with poly(methyl methacrylate) (PMMA) colloidal microspheres followed by embedding in k-carrageenan/polyacrylamide-ethylene glycol (k-CA/PAM-EG) hydrogel. The sensor responded to hazardous gases, including ammonia, toluene, xylene, acetone, methanol, ethanol, and 1-propanol, with a change in the reflection wavelength and visible structural color. At room temperature, the reflection wavelength of the sensor blue-shifted 49 nm in ammonia, and the structural color changed from red to yellow. For low temperatures, the sensor showed great water retention and antifreezing properties even at -57 °C due to the double network. The sensor still had a great response to hazardous gases after freezing at -20 °C for 12 h and testing at 0 °C, and the obtained results were similar to those at room temperature. Based on this excellent stability and visual sensing at low temperature, the sensor demonstrates the potential for detection of hazardous vapors in extreme environments.

Effect of Commercial Black Ink on the Optical Properties of P(St-MMA-AA) Microsphere Photonic Crystal Coating on Wood Surface

The mixed emulsion of P(St-MMA-AA) colloidal microspheres doped with black substances in three commercial inks (pen ink, wood color essence, propylene pigment) was coated on the wood surface. The dried colloidal microspheres self-assembled on the wood surface to form a three-dimensional photonic crystal coating. The influence of the coating on the optical properties of the wood surface was analyzed, and the influence of the type, concentration and drying temperature of the black substance on the structural color coating was explored. When three kinds of commercial black ink were mixed with colloidal microsphere emulsion to obtain photonic crystals on the wood surface, the transmitted light and the scattered light outside the photonic band gap were absorbed by black ink, which effectively reduced the light scattering inside the crystal and significantly enhanced the depth of the photonic crystal structure color. This study utilizes both pigment color and structural color, providing an environmentally friendly and novel method for colored coating of wood surfaces.

SELF-ASSEMBLY AND PHOTOINDUCED DEFORMATION OF MICROSPHERES OF AN AZO MOLECULE CONTAINING A 1,4,3,6-DIANHYDROSORBITOL CORE AND CINNAMATE PERIPHERAL GROUPS

This study investigated the controllable fabrication of anisotropic particles with different sizes and morphologies via self-assembly and photoinduced deformation of azo colloidal microspheres, which were formed from a typical azo molecular material (IAC-4) that contains a 1,4,3,6-dianhydrosorbitol core and the cinnamate peripheral groups. Firstly, azo colloidal microspheres were obtained by self-assembly via gradually adding deionized water into IAC-4 solution of tetrahydrofuran. For precisely controlling the length of short axis of anisotropic particles, IAC-4 colloidal microspheres with different and uniform sizes were obtained by adjusting the IAC-4 concentration, adding rate of water and stirring rate. The size of colloidal microspheres becomes smaller with the increase in IAC-4 concentration, the adding rate of water and the stirring rate. Finally, IAC-4 colloidal microspheres in the solid state, perpendicularly irradiated by the linearly polarized laser beam (λ = 488 nm), were irreversibly and controllably stretched into anisotropic particles with the different morphologies, length of long axis and axial ratio via adjusting the irradiation time and the power of laser beam.

Self-templating synthesis and photocatalytic activity of hollow TiO2 microspheres prepared by the sol–gel + solvothermal method

The microstructure of TiO2 hollow microspheres has a significant impact on the photocatalytic activity, especially the diameter, thickness, specific surface area and crystallinity, which are key factors for structure regulation. In this study, a self-template synthesis strategy for preparing hollow TiO2 hydrate microspheres by the sol–gel+ (methanol) solvothermal method was proposed. With the increase of the H2O/TBOT molar ratio (Rw) in the range of 0.75 ∼ 3.75, amorphous TiO2 colloidal microspheres with flower-like, hollow and solid structures of different sizes were prepared, and the control of TiO2 hydrate hollow microsphere diameters in the range of 1000 nm ∼ 1800 nm was realized. After calcination at 600 °C for 2 h, the structure was not damaged and had good crystallinity. TiO2 hollow spheres of Rw = 1.5 were used for ultraviolet photocatalytic degradation of 20 mg·L-1 phenol for 120 min, and the mineralization rate was >99%, which was better than P25. A series of analyses shows that under the experimental conditions, the hydrolysis rate can be controlled by regulating the H2O/TBOT molar ratio, which is the key factor in the synthesis of different structural sizes.

Capillary adhesion governs the friction behavior of electrochemically corroded polycrystalline diamond

The friction behavior of rough polycrystalline diamond (PCD) surfaces is important in many applications and devices that are required to operate in various harsh environments and it can be argued that a thorough understanding of the friction behavior is essential to the application performance. However, the interplay between electrochemical corrosion, capillary adhesion and friction behavior of PCD in multi-asperity contacts is still poorly understood. In this work, we quantify the interfacial capillary adhesion at contact interfaces and its effect on the friction response, between a colloidal microsphere and rough PCD films before and after electrochemical corrosion, for water-immersed, low RH, and humid air conditions. For these multi-asperity contacts, we demonstrate how electrochemical corrosion influences the surface hydrophilicity of the PCD surfaces, and how capillary adhesion due to water condensation contributes to the friction force. We estimate the capillary forces from both the microscopic lateral force experiments and elastoplastic boundary element method (BEM) contact calculations. The combined results indicate strongly that the observed increase in friction force on electrochemically-corroded PCD surfaces is governed by enhanced capillary adhesion at the contact interface, as affected by surface hydrophilicity and environmental humidity.

Specific Alcohol-Responsive Photonic Crystal Sensors Based on Host-Guest Recognition

A photonic crystal material based on β-cyclodextrin (β-CD) with adsorption capacity is reported. The materials ((A-β-CD)-AM PC) consist of 3D poly (methyl methacrylate) (PMMA) colloidal microsphere arrays and hydrogels supplemented with β-cyclodextrin modified by acryloyl chloride. The prepared materials are then utilized for VOCs gas sensing. The 3D O-(A-β-CD)-AM PC was used to detect toluene, xylene, and acetone and the response was seen as the red-shift of the reflection peak. The 3D I-(A-β-CD)-AM PC was used to detect toluene, xylene, and acetone which occurred redshifted, while methanol, ethanol, and propanol and the peaks' red-shifting was observed. However, among these, methanol gave the largest red-shift response The sensor has broad prospects in the detection of alcohol and the detection of alcohol-loaded drug releases in the future.

Characterizing the Solvent‐Induced Inversion of Colloidal Aggregation During Electrophoretic Deposition

AbstractElectrophoretic deposition (EPD) of colloidal particles is a practical system for the study of crystallization and related physical phenomena. The aggregation is driven by the electroosmotic flow fields and induced dipole moments generated by the polarization of the electrode‐particle‐electrolyte interface. Here, the electrochemical control of aggregation and repulsion in the electrophoretic deposition of colloidal microspheres is reported. The nature of the observed transition depended on the composition of the solvent, switching from electrode‐driven aggregation in water to electrical field‐driven repulsion in ethanol for otherwise identical systems of colloidal microspheres. This work uses optical microscopy‐derived particles and a recently developed particle insertion method approach to extract model‐free, effective interparticle potentials to describe the ensemble behavior of the particles as a function of the solvent and electrode potential at the electrode interface. This approach can be used to understand the phase behavior of these systems based on the observable particle positions rather than a detailed understanding of the electrode‐electrolyte microphysics. This approach enables simple predictability of the static and dynamic behaviors of functional colloid‐electrode interfaces.

Construction of photonic crystals with high color stability on white polyester fabrics

The photonic crystals (PCs) self-assembled by colloidal microspheres interact with light, which can display bright structural colors. Structural color becomes a novel coloring technology for textiles. Normally, structural colors appearing on white polyester fabrics are affected by incoherently scattered light, resulting in low color saturation. This problem can be improved by PCs that were self-assembled from Polystyrene@Polydopamine (PS@PDA) colloidal microspheres with good monodispersity and sphericity. Benefitting from controllable particle size and absorbing incoherently scattered light, PS@PDA PCs can display multiple colors on white polyester fabric. To enhance the color stability of structural color fabrics, the synergistic adhesion effect between polydopamine (PDA) and the P(MMA-BA) colloidal particles at high-temperature melting was exploited. The results showed that the structural color on the white polyester fabric with high saturation and color stability was constructed.

Preparation of Acrylic Yarns with Durable Structural Colors Based on Stable Photonic Crystals.

Structural coloration of photonic crystals (PCs) is considered an ecological and environmental way to achieve colorful textiles. However, constructing PCs with obvious structural colors on traditional flexible yarns is still a great challenge. As a secondary structure that forms textiles, compared with fibers and fabrics, the yarns are rougher, hindering the construction of regular PCs. In this work, the flexible acrylic yarns with vivid structural colors, named PC-based structural color yarns, were prepared by constructing regular PCs via assembling poly(styrene-butyl acrylate-methacrylate) (P(St-BA-MAA)) colloidal microspheres on yarns. Specifically, the properties of P(St-BA-MAA) colloidal microspheres were investigated. The PCs with better structural stability and obvious structural colors were prepared by presetting the acrylic adhesive layer on yarns. Moreover, the color durability and color regulation methods of prepared PC-based structural color yarns were evaluated and discussed. The results showed that the P(St-BA-MAA) colloidal microspheres exhibited even particle sizes, excellent monodispersity, and a typical hard core-soft shell structure. And the glass-transition temperature (T g) of the microspheres was tested to be about 65.6 °C. The cationic acrylate regarded as a pretreatment agent could not only improve the combination between the PC layers and the yarns by acting as a "bridge" but also enhance the structural color effect by smoothing the yarn surface. The results showed that when the mass fraction of cationic acrylate was 3 wt %, the microspheres were beneficial to access regular PCs with obvious structural colors. The PCs with bright structural colors could be constructed on black acrylic yarns, and the colors of yarns were still bright after rubbing and washing tests, indicating that the prepared PC-based structural color yarns have good color fastness. Moreover, the color hue of PC-based structural color yarns could be regulated by adjusting the particle sizes and viewing angles. This study provides strategic support for the structural coloration of flexible materials.