Core-shell Colloids Research Articles

Core–Shell Colloidal Nanocomposites for Local Temperature Monitoring during Photothermal Heating

Core–Shell Colloidal Nanocomposites for Local Temperature Monitoring during Photothermal Heating

Spontaneous Photonic Jammed Packing of Core-Shell Colloids in Conductive Aqueous Inks for Non-Iridescent Structural Coloration.

Integrating structural colors and conductivity into aqueous inks has the potential to revolutionize wearable electronics, providing flexibility, sustainability, and artistic appeal to electronic components. This study aims to introduce bioinspired color engineering to conductive aqueous inks. Our self-assembly approach involves mixing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with sulfonic acid-modified polystyrene (sPS) colloids to generate non-iridescent structural colors in the inks. This spontaneous structural coloration occurs because PEDOT:PSS and sPS colloids can self-assemble into core-shell structures and reversibly cluster into photonic aggregates of maximally random jammed packing within the aqueous environment, as demonstrated by small-angle X-ray scattering. Dissipative particle dynamics simulation confirms that the self-assembly aggregation of PEDOT:PSS chains and sPS colloids can be manipulated by the polymer-colloid interactions. Utilizing the finite-difference time-domain method, we demonstrate that the photonic aggregates of the core-shell colloids achieve close to maximum jammed packing, making them suitable for producing vivid structural colors. These versatile conductive inks offer adjustable color saturation and conductivity, with conductivity levels reaching 36 S cm-1 through the addition of polyethylene glycol oligomer, while enhanced water resistance and mechanical stability are achieved by doping with a cross-linker, poly(ethylene glycol) diglycidyl ether. With these unique features, the inks can create flexible, patterned circuits through processes like coating, writing, and dyeing on large areas, providing eco-friendly, visually appealing colors for customizable, stylish, comfortable, and wearable electronic devices.

Stöber method to amorphous metal-organic frameworks and coordination polymers

The Stöber method is a widely-used sol-gel route for synthesizing amorphous SiO2 colloids and conformal coatings. However, the material systems compatible with this method are still limited. Herein, we have extended the approach to metal-organic frameworks (MOFs) and coordination polymers (CPs) by mimicking the Stöber method. We introduce a general synthesis route to amorphous MOFs or CPs by making use of a base-vapor diffusion method, which allows to precisely control the growth kinetics. Twenty-four different amorphous CPs colloids were successfully synthesized by selecting 12 metal ions and 17 organic ligands. Moreover, by introducing functional nanoparticles (NPs), a conformal amorphous MOFs coating with controllable thickness can be grown on NPs to form core-shell colloids. The versatility of this amorphous coating technology was demonstrated by synthesizing over 100 core-shell composites from 20 amorphous CPs shells and over 30 different NPs. Besides, various multifunctional nanostructures, such as conformal yolk-amorphous MOF shell, core@metal oxides, and core@carbon, can be obtained through one-step transformation of the core@amorphous MOFs. This work significantly enriches the Stöber method and introduces a platform, enabling the systematic design of colloids exhibiting different level of functionality and complexity.

Organic/inorganic heterostructures templated by interfacial instability-driven BCP colloids in deformable emulsion droplets.

Hybrid heterostructure materials have received considerable attention due to the integration of each component and abundant functional applications in micromotors, catalysis, photothermal therapy, drug delivery, and bioimaging. However, the preparation of organic/inorganic heterostructure nanoparticles (HSNPs) with high quality still remains a remarkable challenge since thermodynamically metastable structures usually coexist, resulting in a lack of organic scaffolds with extreme uniformity both in shape and size distribution. Here, we prepared polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) core-shell spherical colloids driven by interfacial instability of soft and deformable emulsion droplets. Ultra-low interfacial tension was achieved through the co-adsorption of BCP segments and sodium dodecyl sulfate (SDS) surfactant, which had a strong affinity with the P4VP segment at the interface of the emulsified droplets. The excellent and homogeneous BCP colloids were further utilized as organic scaffolds to selectively grow a functional SiO2 layer on the surface of the BCP spherical colloids, producing BCP/SiO2 HSNPs with highly uniform shape and size distribution originating from the PS-b-P4VP scaffolds, thus providing an efficient and general strategy to construct and design organic/inorganic HSNPs with diverse applications.

Easy Cell Detachment and Spheroid Formation of Induced Pluripotent Stem Cells Using Two-Dimensional Colloidal Arrays

Induced pluripotent stem cells (iPSCs) may develop into any form of cell and are being intensively investigated. The influence on iPSCs of nanostructures generated using two-dimensional colloidal arrays was examined in this study. Colloidal arrays were formed using the following procedure. First, core–shell colloids were adsorbed onto a glass substrate using a layer-by-layer method. Second, the colloids were immobilized via thermal fusion. Third, the surface of the colloids was modified by plasma treatment. By adjusting the number density of colloids, cultured iPSCs were easily detached from the substrate without manual cell scraping. In addition to planar culture, cell aggregation of iPSCs attached to the substrate was achieved by combining hydrophilic surface patterning on the colloidal array. Multilayered cell aggregates with approximately four layers were able be cultured. These findings imply that colloidal arrays might be an effective tool for controlling the strength of cell adhesion.

Template-Directed Polymerization of Binary Acrylate Monomers on Surface-Activated Lignin Nanoparticles in Toughening of Bio-Latex Films.

Fabricating bio-latex colloids with core-shell nanostructure is an effective method for obtaining films with enhanced mechanical characteristics. Nano-sized lignin is rising as a class of sustainable nanomaterials that can be incorporated into latex colloids. Fundamental knowledge of the correlation between surface chemistry of lignin nanoparticles (LNPs) and integration efficiency in latex colloids and from it thermally processed latex films are scarce. Here, an approach to integrate self-assembled nanospheres of allylated lignin as the surface-activated cores in a seeded free-radical emulsion copolymerization of butyl acrylate and methyl methacrylate is proposed. The interfacial-modulating function on allylated LNPs regulates the emulsion polymerization and it successfully produces a multi-energy dissipative latex film structure containing a lignin-dominated core (16% dry weight basis). At an optimized allyl-terminated surface functionality of 1.04mmol g-1 , the LNPs-integrated latex film exhibits extremely high toughness value above 57.7MJ m-3 . With multiple morphological and microstructural characterizations, the well-ordered packing of latex colloids under the nanoconfinement of LNPs in the latex films is revealed. It is concluded that the surface chemistry metrics of colloidal cores in terms of the abundance of polymerization-modulating anchors and their accessibility have a delicate control over the structural evolution of core-shell latex colloids.

In situ single particle characterization of the themoresponsive and co-nonsolvent behavior of PNIPAM microgels and silica@PNIPAM core-shell colloids

Poly(N-isopropylacrylamide) (PNIPAM) microgels and PNIPAM colloidal shells attract continuous strong interest due to their thermoresponsive behavior, as their size and properties can be tuned by temperature. The direct single particle observation and characterization of pure, unlabeled PNIPAM microgels in their native aqueous environment relies on imaging techniques that operate either at interfaces or in cryogenic conditions, thus limiting the observation of their dynamic nature. Liquid Cell (Scanning) Transmission Electron Microscopy (LC-(S) TEM) imaging allows the characterization of materials and dynamic processes such as nanoparticle growth, etching, and diffusion, at nanometric resolution in liquids. Here we show that via a facile post-synthetic in situ polymer labelling step with high-contrast marker core–shell Au@SiO2 nanoparticles (NPs) it is possible to determine the full volume of PNIPAM microgels in water. The labelling allowed for the successful characterization of the thermoresponsive behavior of PNIPAM microgels and core shell silica@PNIPAM hybrid microgels, as well as the co-nonsolvency of PNIPAM in aqueous alcoholic solutions. The interplay between electron beam irradiation and PNIPAM systems in water resulted in irreversible shrinkage due to beam induced water radiolysis products, which in turn also affected the thermoresponsive behavior of PNIPAM. The addition of 2-propanol as radical scavenger improved PNIPAM stability in water under electron beam irradiation.

Silica-Encapsulated Germania Colloids as 3D-Printable Glass Precursors.

Core–shell colloids make attractive feedstocks for three-dimensional (3D) printing mixed oxide glass materials because they enable synthetic control of precursor dimensions and compositions, improving glass fabrication precision. Toward that end, we report the design and use of core–shell germania–silica (GeO2–SiO2) colloids and their use as precursors to fabricate GeO2–SiO2 glass monoliths by direct ink write (DIW) 3D printing. By this method, GeO2 colloids were prepared in solution using sol–gel chemistry and formed oblong, raspberry-like agglomerates with ∼15 nm diameter primary particles that were predominantly amorphous but contained polycrystalline domains. An ∼15 nm encapsulating SiO2 shell layer was formed directly on the GeO2 core agglomerates to form core–shell GeO2–SiO2 colloids. For glass 3D printing, GeO2–SiO2 colloidal sols were formulated into a viscous ink by solvent exchange, printed into monoliths by DIW additive manufacturing, and sintered to transparent glasses. Characterization of the glass components demonstrates that the core–shell GeO2–SiO2 presents a feasible route to prepare quality, optically transparent low wt % GeO2–SiO2 glasses by DIW printing. Additionally, the results offer a novel, hybrid colloid approach to fabricating 3D-printed Ge-doped silica glass.

Curcumin loaded core-shell biopolymers colloid and its incorporation in Indian Basmati rice: An enhanced stability, anti-oxidant activity and sensory attributes of fortified rice

Curcumin, a major bioactive in curcuminoids and food colorant, possess therapeutic properties, however, its low water solubility, instability during processing limit its industrial applications. The nanoencapsulated curcumin (NEC) in sodium caseinate (SC) and Maillard conjugate (MC) showed >90% water solubility. Encapsulation in MC reduced particle size (150 to 120 nm) zeta potential (−34 to −45 mV) and improved encapsulation efficiency (74 to 94%) compared to SC under optimized Tween20 and salt-ions. The in-vitro bioaccessibility of NEC was 300% more than curcumin (pH 7.4). The curcumin (0.092 mmol) and spray-dried NEC (0–0.092 mmol) were incorporated in Indian Basmati rice. The UV–VIS revealed 14, 10% higher stability of NEC (0.069 mmol) incorporated rice under dark and light at 27 ± 2 °C and 43, 39% more in thermally processed limited and excess water conditions, respectively, than curcumin. The high visual appeal and anti-oxidant activity (60%) of NEC Basmati rice demonstrated application in fortified product development.

Macroporous Silica Foams Fabricated via Soft Colloid Templating.

Macroporous materials with controlled pore sizes are of high scientific and technological interest, due to their low specific weight, as well as unique acoustic, thermal, or optical properties. Solid foams made of titania, silica, or silicon, as representative materials, have been previously obtained with several hundred nanometer pore sizes, by using sacrificial templates such as spherical emulsion droplets or colloidal particles. Macroporous structures in particular are excellent candidates as photonic materials with applications in structural coloration and photonic bandgap devices. However, whereas using spherical building blocks as templates may provide tight control over pore shape and size, it results in materials with an often unfavorable local topology. Templating dry-foam or compressed-emulsion structures appear as attractive alternatives, but have not been demonstrated so far for submicron pore sizes. Herein, the use of soft, flexible microgel colloids decorated with silica nanoparticles as templates of macroporous foams is reported. These purposely synthesized core-shell colloids are assembled at ultra-high effective volume fractions by centrifuging and thermal swelling, thereby resulting in uniform disordered materials with facetted pores, mimicking dry foams. After removal of the polymer component via calcination, lightweight pure silica structures are obtained with a well-defined cellular or networktopology.

Shape Matters in Magnetic-Field-Assisted Assembly of Prolate Colloids.

An anisotropic colloidal shape in combination with an externally tunable interaction potential results in a plethora of self-assembled structures with potential applications toward the fabrication of smart materials. Here we present our investigation on the influence of an external magnetic field on the self-assembly of hematite-silica core–shell prolate colloids for two aspect ratios ρ = 2.9 and 3.69. Our study shows a rather counterintuitive but interesting phenomenon, where prolate colloids self-assemble into oblate liquid crystalline (LC) phases. With increasing concentration, particles with smaller ρ reveal a sequence of LC phases involving para-nematic, nematic, smectic, and oriented glass phases. The occurrence of a smectic phase for colloidal ellipsoids has been neither predicted nor reported before. Quantitative shape analysis of the particles together with extensive computer simulations indicate that in addition to ρ, a subtle deviation from the ideal ellipsoidal shape dictates the formation of this unusual sequence of field-induced structures. Particles with ρ = 2.9 exhibit a hybrid shape containing features from both spherocylinders and ellipsoids, which make their self-assembly behavior richer than that observed for either of the “pure” shapes. The shape of the particles with higher ρ matches closely with the ideal ellipsoids, as a result their phase behavior follows the one expected for a “pure” ellipsoidal shape. Using anisotropic building blocks and external fields, our study demonstrates the ramifications of the subtle changes in the particle shape on the field-directed self-assembled structures with externally tunable properties.

Exploiting the Transformative Features of Metal Halides for the Synthesis of CsPbBr3@SiO2 Core–Shell Nanocrystals

The encapsulation of colloidal lead halide perovskite nanocrystals within silica (SiO2) is one of the strategies to protect them from polar solvents and other external factors. Here, we demonstrate the overcoating of CsPbBr3 perovskite nanocrystals with silica by exploiting the anhydride-induced transformation of Cs4PbBr6 nanocrystals. CsPbBr3@SiO2 core–shell nanocrystals are obtained after (i) a reaction between colloidal Cs4PbBr6 nanocrystals and maleic anhydride in toluene that yields CsPbBr3 nanocrystals and maleamic acid and (ii) a silica-shell growth around CsPbBr3 nanocrystals via hydrolysis of added alkoxysilanes. The reaction between Cs4PbBr6 nanocrystals and maleic anhydride is necessary to promote shell formation from alkoxysilanes, as demonstrated in control experiments. The best samples of as-prepared CsPbBr3@SiO2 nanocrystals consist of ∼10 nm single-crystal CsPbBr3 cores surrounded by ∼5–7 nm amorphous silica shell. Despite their core–shell structure, such nanostructures are poor emitters and degrade within minutes of exposure to ethanol. The photoluminescence intensity of the core–shell nanocrystals is improved by the treatment with a solution of PbBr2 and ligands, and their stability in ethanol is extended to several days after applying an additional silica growth step. Overall, the investigated approach outlines a strategy for making colloidal core–shell nanocrystals utilizing the transformative chemistry of metal halides and reveals interesting insights regarding the conditions required for CsPbBr3@SiO2 nanocrystal formation.

Theoretical investigation of intersubband optical properties of ‘giant’ colloidal core–shell quantum dot with alloyed interfacial layer

We have theoretically modeled the “giant” colloidal core–shell quantum dot with strain adapting alloyed interfacial layer between core and shell materials for optoelectronic applications. The intersubband optical properties, such as absorption coefficients (ACs), refractive index changes (RICs), oscillator strength, and transition lifetime of giant CdSe / CdSexS1 − x / CdS core–interfacial–shell quantum dot (g-CISQD) have been investigated for different alloying “x” of the interfacial layer with varying core radius. The results have been plotted considering the significant impact of strain between the heterojunctions and compared for different structural parameters. The results show that the oscillator strength and transition lifetime strongly depend on alloying x and core radius. The energy eigenvalue in g-CISQD decreases with increasing x and saturates beyond the value x = 0.5. The resultant redshift of the resonant peak in ACs and RICs is concurrence with the obtained energy eigenvalues. Further, the ACs and RICs have been investigated for different intensities of incident light ( I ) and core radius variation. The results provide the tuning possibility of the optical properties using appropriate alloying x and core radius for application in optoelectronic devices.

Three-Dimensional Colloidal Controlled Growth of Core-Shell Heterostructured Persistent Luminescence Nanocrystals.

Persistent luminescence nanoparticles (PLNPs) are an emerging photonic nanomaterial that possesses uniquely persistent luminescence properties after excitation ceases. They can be repeatedly recharged in vitro and in vivo and hold great promise for numerous areas and applications. Unfortunately, none of the existing synthesis methods can control their composition to grow core-shell structured PLNPs with desirable shapes and enhanced functionalities. Here, we report on straightforward thermolysis-mediated colloidal synthesis of CaF2:Dy@NaYF4 core-shell PLNPs that can enhance persistent luminescence under both light and X-ray excitations. Benefitting from the well-matched crystal lattices between CaF2 and NaYF4, this colloidal synthesis makes it possible to prepare core-shell PLNPs with exquisite control of the compositions, shapes, and enhanced luminescence. This demonstration of the developing colloidal core-shell PLNPs overcomes the current key bottleneck regarding the synthesis of heterostructured PLNPs and sets the stage for fully exploiting the potential of these fascinating luminous materials.

Transient dynamics of soft particle glasses in startup shear flow. Part I: Microstructure and time scales

The rheology and microstructure of soft particle glasses during startup flow are studied using three-dimensional particle dynamics simulations at different particle volume fractions and shear rates. The behavior of transient stress depends on the applied shear rate. At high shear rates, soft particle glasses exhibit a static yield stress signaled by a stress overshoot followed by a relaxation to a steady-state value. The buildup of the stress is driven by an interplay between structural anisotropy due to an accumulation of particles along the compression axis and a depletion along the extension axis and a compression of particles that are soft and deformable. At low shear rates, the stress increase is monotonic and without any stress overshoot. The time scale at which structural anisotropy and the stress are maximum is correlated to the nonaffine dynamics of SPGs through the persistence time of shear-induced particle collisions and to the residence time of particles inside their transient cages. The static yield strain γ p and the reduced static yield stress σ p / σ y, where σ y is the dynamic yield stress deduced from steady flow measurements, follow universal behaviors when correlated with the dimensional shear rate η s γ ˙ / G 0, with η s being the suspending fluid viscosity and G 0 the storage modulus, which expresses the competition between elastic restoring forces and viscous dissipation. Dense suspensions of thermosensitive core–shell colloids, star-like micelles, and poly(ethylene oxide)-protected silica particles follow the same universal curves, suggesting the generality of our results.

Theoretical modeling of a “giant” colloidal core–shell quantum dot with an alloyed interfacial layer for solar cell applications

We proposed a theoretical modeling of a “giant” colloidal core–shell quantum dot with a strain-adapting alloyed interfacial layer between the core and shell materials for solar cell applications. The recently modified detailed balance model [J. Appl. Phys. 125, 174302 (2019)JAPIAU0021-897910.1063/1.5086015] is further modified in this paper to obtain a more realistic conversion efficiency (CE) of the C d S e / C d S e x S 1 − x / C d S quantum dot solar cell. This proposed model computes the CE, considering the significant impact of the energy gap and oscillator strength simultaneously. The CE is investigated for different alloying factors “ x ” by considering the strain effect between the heterostructure. The results obtained in terms of CE and photoluminescence peak wavelength nearly approximate the experimental studies of similar dot structure and dimensions.

Tunable Circular Dichroism by Photoluminescent Moiré Gratings

AbstractIn nanophotonics, there is a current demand for ultrathin, flexible nanostructures that are simultaneously easily tunable, demonstrate a high contrast, and have a strong response in photoluminescent polarization. In this work, the template‐assisted self‐assembly of water‐dispersed colloidal core–shell quantum dots into 1D light‐emitting sub‐micrometer gratings on a flexible substrate is demonstrated. Combining such structures with a light‐absorbing metallic counterpart by simple stacking at various angles results in a tunable Moiré pattern with strong lateral contrast. Furthermore, a combination with an identical emitter‐based grating leads to a chiroptical effect with a remarkably high degree of polarization of 0.72. Such a structure demonstrates direct circular polarized photoluminescence, for the first time, without a need for an additional chiral template as an intermediary. The suggested approach allows for reproducible, large‐area manufacturing at reasonable costs and is of potential use for chiroptical sensors, photonic circuit applications, or preventing counterfeit.

Preparation and Tracking of Oblate Core-Shell Polymethyl-Methacrylate Ellipsoids.

Although single-particle level studies on prolate ellipsoidal colloids are relatively abundant, similar studies on oblate ellipsoids are rare because suitable model systems are scarcely available. Here, we present the preparation of monodisperse hard core-shell oblate ellipsoids that can be imaged and tracked in 3D with confocal laser scanning microscopy. Using a thermomechanical squeezing method, we transform spherical core-shell polymethyl-methacrylate (PMMA) particles into oblate ellipsoids. We show how the shape polydispersity as well as the aspect ratio of the obtained oblate ellipsoids can be controlled. In addition, we discuss how the core-shell geometry limits the range of aspect ratios because of the different viscoelastic properties of the cross-linked PMMA core and linear PMMA shell. We further demonstrate imaging of the core-shell oblate dispersions on a single-particle level in real space and time and the tracking of position and orientation using our recently developed tracking algorithm for anisotropic core-shell colloids. Our results thus provide the tools for the future investigation of the behavior of oblate ellipsoids, especially in dense suspensions.

Impact of oppositely charged shell and cores on interaction of core-shell colloids with differently charged proteins as a route for tuning of the colloids cytotoxicity

The present work represents interactions between the core-shell nanoparticles and different proteins, exemplified by lysozyme (LSZ), pepsin, bovine serum albumin (BSA), thioredoxin (TRX) and yellow fluorescent protein (YFP). The core-shell morphology derives from the non-covalent deposition of polyethyleneimine (PEI) onto nanoprecipitated luminescent complex (AuCl)2L (L is cyclic PNNP ligand). Analysis of the data obtained by DLS, CD spectroscopy, luminescence derived from both (AuCl)2L and YFP reveal the electrostatically driven interaction of negatively charged proteins with the shell of PEI-(AuCl)2L. The fluorescence of YFP enables to reveal the inclusion of the protein molecules into the shell. The lack of any luminescent response of PEI-(AuCl)2L on TRX conforms its electrostatically driven interactions with the shell which, in turn, excludes a binding of the exposed thiol moieties with (AuCl)2L. The negatively charged surface of pepsin provides the greatest recharging of the PEI-based shell versus the other proteins, which is followed by the enhanced luminescence of (AuCl)2L. The significant effect of PEI-(AuCl)2L on the CD spectra of LSZ followed by the decreased intensity of (AuCl)2L-based luminescence points to specific interaction mode of PEI-(AuCl)2L with LSZ. The flow cytometry and fluorescent microscopy measurements revealed efficient internalization of PEI-(AuCl)2L into the Wi-38 cell samples resulting in the efficient staining of all cell organelles. The concentration dependent cytotoxicity of PEI-(AuCl)2L is detectably enhanced by LSZ, which is correlated with its interaction mode with the nanoparticles.

Energetic characteristics of the Al/CuO core-shell composite micro-particles fabricated as spherical colloids

Metastable intermolecular composites (MICs) exhibit applications in supplying thermal energy to miniature systems, although they are commonly fabricated as powders, films, multi-layers and other heterostructures which desire an effective interface between reactive components but are not colloids and typically immobile. Little information is available in the literature on fabrication and characterization of standing-alone and mobile core-shell MIC micro-particles. In this paper, we report on a wet-chemistry method to synthesize micron-sized spherical colloids of Al/CuO with a core-shell structure. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were employed to characterize the micro-structure and element distribution at the Al/CuO interface, while differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to examine the thermochemical properties of these MIC spherical particles. It was found that for these core-shell micron-sized particles, the onset temperature (about 580⁰C) corresponding to the exothermic reaction is similar to that of the powder mixtures composed of Al and CuO nanoparticles (around 548⁰C), while the activation energy of the former (328 kJ/mol) is much lower than that of the latter (438 kJ/mol). Direct contact and subsequent solid-state diffusion of reactive components at the interface of the Al/CuO core-shell are attributed to these experimental observations. The specific energy release (807 J/g) is however significantly smaller than that of the nano-powder mixtures (1107 J/g) due to the limited thickness of the CuO shell which is originated from the restrictions of the wet chemistry method. Future work includes testing the energetic performance of these core-shell colloids in a liquid or solution ambient.