Core-shell Hybrid Particles Research Articles

Clickable periodic mesoporous organosilicas core-shell particles with radially-oriented mesopores for high-performance liquid chromatography

It is important to explore well-defined materials to further improve the performance of chromatographic stationary phase. Periodic mesoporous organosilica (PMO) with uniform-distributed organic functionalities and high chemical stability is rising star of chromatography. In this work, ethylene-bridged PMO with excellent organization over distances of several dozen nm was coated on silica cores to form core-shell particles with radially-oriented mesopores. The separation performance for naphthalene was 9.7 × 104 plates/m after derivatization of the C18 group on the terminal vinyl of vinyltriethoxysilane by “thiol-ene” click reaction. These hybrid core-shell particles had good mechanical strength, as well as adequate chemical stability (0.1%TEA, pH 9.5), so it has the potential for HPLC separation.

Next-generation ecofriendly MR fluid: Hybrid GO/ Fe2O3 encapsulated carbonyl iron microparticles with improved magnetorheological, tribological, and corrosion resistance properties

In this study, magnetorheological fluid (MRF) was developed using hybrid core-shell particles. The core of these particles consists of carbonyl iron (CI), while the shell is composed of graphene oxide (GO) and iron oxide (Fe2O3) nanocomposite particles. The hybrid nanocomposite and core-shell particles were synthesized through a simple wet stirring process. A blended biocompatible oil comprising 90% rice bran oil and 10% silicone oil was employed as the continuous phase to ensure environmental and economic feasibility. Various characterization techniques were employed to examine the surface, structural, and magnetic properties of the hybrid core-shell particles. Magnetorheological (MR) measurements demonstrated that the incorporation of GO/Fe2O3 nanocomposite particles onto the CI particles (CIPs) significantly enhanced the shear stress and yield stress properties of the resulting MRF. This improvement can be ascribed to an increase in the magnetic saturation resulting from the encapsulation of GO-decorated Fe2O3 nanocomposite particles. The corrosion resistance and sedimentation properties were evaluated in this study, and the hybrid core-shell particles exhibited superior results compared to the bare CIPs. In terms of tribological performance, the hybrid core-shell particles exhibited significant improvement in friction and wear properties in comparison to the bare CIPs-based MRF and dry sliding condition. The significant reduction in coefficient of friction (COF) and wear might be attributed to the development of a lubricating protective layer consisting of bare CIPs and hybrid core-shell particles-based MR fluids (MRFs) at the contact interface. Consequently, this study offers an economical and effective approach for formulating MRFs with desirable rheological and tribological characteristics and corrosion inhibition properties, making them suitable for various environmental and industrial applications.

Imaging Radial Distribution Functions of Complex Particles by Relayed Dynamic Nuclear Polarization.

The physical properties of many modern multi-component materials are determined by their internal microstructure. Tools capable of characterizing complex nanoscale architectures in composite materials are, therefore, essential to design materials with targeted properties. Depending on the morphology and the composition, structures may be measured by laser diffraction, scattering methods, or by electron microscopy. However, it can be difficult to obtain contrast in materials where all the components are organic, which is typically the case for formulated pharmaceuticals, or multi-domain polymers. In nuclear magnetic resonance (NMR) spectroscopy, chemical shifts allow a clear distinction between organic components and can in principle provide the required chemical contrast. Here, we introduce a method to obtain radial images of the internal structure of multi-component particles from NMR measurements of the relay of nuclear hyperpolarization obtained from dynamic nuclear polarization. The method is demonstrated on two samples of hybrid core-shell particles composed of a core of polystyrene with a shell of mesostructured silica filled with the templating agent CTAB and is shown to yield accurate images of the core-shell structures with a nanometer resolution.

Hybrid core-shell particles for mRNA systemic delivery.

mRNA based infectious disease vaccines have opened the venue for development of novel nucleic acids-based therapeutics. For all mRNA therapeutics dedicated delivery systems are required, where different functionalities and targeting abilities need to be optimized for the respective applications. One option for advanced formulations with tailored properties are lipid-polymer hybrid nanoparticles with complex nanostructure, which allow to combine features of several already well described nucleic acid delivery systems. Here, we explored hyaluronic acid (HA) as coating of liposome-mRNA complexes (LRCs) to investigate effects of the coating on surface charge, physicochemical characteristics and biological activity. HA was electrostatically attached to positively charged complexes, forming hybrid LRCs (HLRCs). At different N/P ratios, physico-chemical characterization of the two sets of particles showed similarity in size (around 200nm) and mRNA binding abilities, while the presence of the HA shell conferred a negative surface charge to otherwise positive complexes. High transfection efficiency of LRCs and HLRCs in vitro has been obtained in THP-1 and human monocytes derived from PBMC, an interesting target cell population for cancer and immune related pathologies. In mice, quantitative biodistribution of radiolabeled LRC and HLRC particles, coupled with bioluminescence studies to detect the protein translation sites, hinted towards both particles' accumulation in the hepatic reticuloendothelial system (RES). mRNA translated proteins though was found mainly in the spleen, a major source for immune cells, with preference for expression in macrophages. The results showed that surface modifications of liposome-mRNA complexes can be used to fine-tune nanoparticle physico-chemical characteristics. This provides a tool for assembly of stable and optimized nanoparticles, which are prerequisite for future therapeutic interventions using mRNA-based nanomedicines.

Enhancement of Si3N4@MoS2 core–shell structure on wear/corrosion resistance of epoxy resin/polyacrylate IPN composite coating

To enhance the interfacial interaction between Si3N4 and epoxy resin/polyacrylate interpenetrating polymer network (IPN) and exert the synergistic effect between Si3N4 and MoS2, Si3N4@MoS2 core–shell hybrid particles (CSs) were successfully prepared by simple hydrothermal method. The as-prepared CSs can significantly enhance the tribological and anti-corrosion properties of epoxy resin/polyacrylate IPN organic matrix. Compared with pure epoxy resin/polyacrylate IPN organic matrix, the composite coating with the optimal amount of 1.5 wt% CSs displays lower friction coefficient and wear rate (reduced by 82% and 83%, respectively), and its impedance modulus at low frequency is increased by 3 orders of magnitude. The enhancement of CSs is mainly attributed to the synergy between Si3N4 with high hardness and MoS2 with self-lubrication and shielding effect of MoS2. Furthermore, Si3N4@MoS2 core–shell structure with synergistic performance characteristics can also effectively enhance the tribocorrosion resistance of epoxy resin/polyacrylate IPN organic matrix. CSs are regarded as promising additive toward wear resistance and corrosion protection.

Synthesis and characterization of core-shell nanoparticles and their application in dental resins

The aim of this study was to synthesize acrylic core-shell particles and silica-loaded core-shell hybrid particles through emulsion polymerization. Also this work examined the influence of synthesized nanoparticles loading in a Bis-GMA/TEGDMA resin matrix on some mechanical properties of the dental composite resins. Core-shell particles consisting of polybutyl acrylate (PBA) rubbery core and polymethyl methacrylate (PMMA)/polystyrene (PS) shell were synthesized by seeded emulsion polymerization. For preparing the core-shell hybrid particles, first silica particles with diameters of about 68 nm were synthesized based on the Stöber process. Then the surface of silica particles was treated with ɣ-MPS. Afterwards, polymeric shell was coated on silica nanoparticles through emulsion polymerization. The morphology of core-shell particles was examined by SEM/TEM. Mechanical properties (fracture toughness, flexural strength and flexural modulus) of the photo-cured Bis-GMA/TEGDMA dental resins/composites filled with different mass fractions of synthesized nanoparticles were tested, and analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. Formation of glassy shell on PBA core in core-shell particles, grafting of ɣ -MPS onto the silica particles and encapsulation of modified silica by polymeric shell in core-shell hybrid particles were confirmed using various analytical techniques. The results of mechanical tests showed that fracture toughness of Bis-GMA/TEGDMA dental resins improved about 35% by the inclusion of 5 wt% silica-loaded core-shell hybrid particles with little effect on flexural strength. This study shows that incorporation of proper amount of hybrid core-shell particles in dental composites can improve their fracture toughness and thus may extend their service life.

Weak Polyampholytes at the Interface of Magnetic Nanocarriers: A Facile Catch-and-Release Platform for Dyes.

We present a platform of charge-invertible core-shell hybrid particles for the selective and reversible adsorption of small charged molecules as model systems. The herein employed carrier systems consist of an iron oxide core coated with different pH-responsive polyampholytes which exhibit varying surface charge depending on the surrounding pH value. The resulting materials were used for electrostatically mediated catch-and-release experiments of either cationic or anionic dyes with the perspective to allow the pH-dependent magnetically guided transport of suitable cargo. The use of three different polyampholyte coatings (poly(2-(imidazol-1-yl)acrylic acid) (PImAA), poly(dehydroalanine) (PDha), and poly(N,N-diallylglutamate) (PDAGA)) enables a deeper understanding about how the surface net charge in combination with the charge and charge density of any cargo influences such processes. The size, surface charge, and aggregation behavior of the herein described particles were investigated via dynamic light scattering (DLS), transmission electron microscopy (TEM), and pH-dependent ζ-potential measurements, whereas adsorption and release studies were investigated via UV-vis.

Magnetic/Gold Core-Shell Hybrid Particles for Targeting and Imaging-Guided Photothermal Cancer Therapy.

The development of hybrid particles for tumor diagnosis and therapy has received considerable attention because they are capable of combining tumor diagnosis and treatment concurrently. So far hybrid particles for efficient and safe tumor theranostics are still very limited. Herein we have designed a new type of hybrid particles and evaluated its potential to be used in image-guided cancer diagnosis and therapy without the need of any toxic anticancer or contrast agents. The hybrid particles, consist of magnetic nanoparticles which are embedded in the poly(methyl methacrylate) (PMMA) cores and gold shells on chitosan (CTS) (γ-Fe₂O₃ @PMMA/CTS@Au). The hybrid particles were synthesized through initial formation of the core-shell structured γ-Fe₂O₃ @PMMA/CTS particles containing approximately 20% loading of magnetic nanoparticles. A gold layer was then built on top of the core-shell magnetic particles via a reduction of gold salt by amines from the chitosan assisted with the reducing agent NaBH₄, followed by growing to complete gold shells in the presence of ascorbic acid (42.6% Au content). The properties of the composite particles including their chemical composition, morphology, particle size, size distribution, surface charge, magnetic responsiveness and photothermal ability were systematically characterized. The potential application of the γ-Fe₂O₃ @PMMA/CTS@Au hybrid particles in tumor diagnosis and therapy was assessed in vitro and in vivo using 4T1 tumor cells and 4T1 tumor-bearing mice through combining magnetic targeting, photoacoustic (PA)/computed tomography (CT) imaging and photothermal therapy. Results suggest that the γ-Fe₂O₃ @PMMA/CTS@Au particles can serve as a multifunctional tumor theranostic nanoplatform for magnetically targeted photothermal therapy. Breast cancer has been effectively eliminated without the use of any anticancer drugs or contrast agents. Therefore, this type of core-shell hybrid particles represents a new composite particle design for effective and safe tumor theranostics.

Preparation of PS/PVP/TiO₂ Core-Shell Particles Under Various Reaction Factors.

The present study deals with the formation of monodisperse sub-micron sized PS/PVP/TiO₂ core- shell hybrid particles via in situ sol-gel method and the effects of varying concentrations of polystyrene seed latex and TBOT, amount and addition rate of water, and sonication power. These reaction factors were found to be closely related to the final particle size, TiO₂ shell thickness, particle density, refractive index, and thermal properties. The particle densities and the refractive indices of the resulting PS/PVP/TiO₂ core-shell hybrid particles were in the range of 2.71~3.69 g/cm³ and 1.63~2.12, respectively.

Measurements of Particle-Surface Interactions in Both Equilibrium and Nonequilibrium Systems.

Total internal reflection microscopy (TIRM) is a passive technique that measures colloidal interactions in aqueous solution. A traditional Boltzmann method requires that particles must fluctuate around equilibrium positions for a long time. A method based on multiparticle tracking and drift velocity method was developed to measure interactions in both equilibrium and nonequilibrium systems. This method relaxed the limitation of the traditional Boltzmann method and do not require any external force like optical tweezer. Theoretical predictions of particle sedimentation under the influence of various forces were investigated to determine the proper particle size and solution properties. We found that the polystyrene (PS) particle with a size of 2.1 μm took the longest time to finish sedimentation, and 5% (w/w) sucrose was chosen to suppress the Brownian motion. For single and ensemble particles in equilibrium, the experimental diffusion coefficients and potential energy profiles were consistent with the theoretical prediction. In nonequilibrium experiments, the van der Waals force between the bare/hybrid particles and flat surface was measured, and the silica shell acted to strengthen the van der Waals attraction. This method extends the application of TIRM to nonequilibrium systems without any active control. Moreover, the silica-coated PS core-shell hybrid particles facilitate surface modification with a variety of active chemicals. It would be a great advantage to measure all kinds of long-range interactions between surface-modified particles and surface in aqueous solution with TIRM.

Synthesis and characterization of PNIPAM microgel core–silica shell particles

We developed a simple effective approach to prepare poly(N-isopropylacrylamide-co-acrylamide-co-N,N′-methylenebisacrylamide) (PNIPAM/AM/MBA) microgel core–silica shell particles with narrow particle size distribution via the sol–gel reaction of silica precursor deposited directly on the microgel particle surface in the presence of 3-glycidyloxypropyltrimethoxysilane (GLYMO). MBA was used as the cross-linking agent for the formation of microgel with the cross-linked network structure and GLYMO used as a coupling agent. The morphology of hybrid core–shell particles including the shape, core size, shell thickness and surface roughness was governed by the key components of AM and GLYMO. PNIPAM/AM/MBA microgel core–silica shell particles show desirable spherical shape, distinct core–shell structure and raspberry-like particle morphology. In contrast, PNIPAM/MBA microgel core–silica shell particles formed without resort to AM and GLYMO result in very poor silica encapsulation, thereby leading to undesired particle morphology. Incorporation of AM units into PNIPAM/MBA microgel particles increases the lower critical solution temperature (LCST). Furthermore, encapsulation of PNIPAM/AM/MBA microgel particles by silica does not affect the LCST to an appreciable extent, but it greatly reduces the thermo-sensitivity of the hybrid core–shell particles. Finally, the feasibility of using these PNIPAM-based core–silica shell particles as drug carriers was demonstrated.

Surface-initiated ATRP from polydopamine-modified TiO2 nanoparticles

A robust approach for modification of TiO2 nanoparticles with polymer brushes by atom transfer radical polymerization (ATRP) is presented. TiO2 surface was first coated with polydopamine (PDA) followed by immobilization of an ATRP initiator, α-bromoisobutyryl bromide (BiBB). Poly(methyl methacrylate) (PMMA) and poly(butyl acrylate) (PBA) were then grafted from the PDA-modified TiO2 of different size (25 and 300 nm) in DMF at room temperature via supplemental activator reducing agent (SARA) ATRP using only 100 ppm of the copper catalyst. Hybrid core-shell particles with high organic contents (40–88 wt%) and grafting densities (0.16–0.25 nm−2) were obtained. Reaction conducted in the presence of sacrificial initiator confirmed excellent control over the polymerization and produced PMMA and PBA with narrow molecular weight distributions (Mw/Mn < 1.25). Obtained particles were tested as lubricating additives in pipe dope compositions. Addition of polymer-grafted TiO2 to the base grease resulted in a reduced coefficient of friction (COF) and wear over uncoated TiO2 as revealed by reciprocating pin-on-disc tests. The model pipe dopes with PMMA-grafted particles were found to perform on par with commercial American Petroleum Institute (API) dope.

Exactly solvable model for self-assembly of hard core-soft shell particles at interfaces.

A generic model for self-assembly of a monolayer of hybrid core-shell particles at an interface is developed. We assume that for distances larger than the size of the incompressible core a soft repulsion appears, and the repulsion is followed by an attraction at larger separations. The model is solved exactly in a one-dimensional lattice version. One, two or three periodic structures and variety of shapes of the pressure-density isotherms may occur in different versions of the model. For strong interactions the isotherm consists of nearly vertical segments at densities optimal for the periodic structures that are connected by segments with a small slope. The range of order depends very strongly on the strength of attraction and on the density. Our results agree with experimental observations.

Polystyrene-Core-Silica-Shell Hybrid Particles Containing Gold and Magnetic Nanoparticles.

Polystyrene-core-silica-shell hybrid particles were synthesized by combining the self-assembly of nanoparticles and the polymer with a silica coating strategy. The core-shell hybrid particles are composed of gold-nanoparticle-decorated polystyrene (PS-AuNP) colloids as the core and silica particles as the shell. PS-AuNP colloids were generated by the self-assembly of the PS-grafted AuNPs. The silica coating improved the thermal stability and dispersibility of the AuNPs. By removing the "free" PS of the core, hollow particles with a hydrophobic cage having a AuNP corona and an inert silica shell were obtained. Also, Fe3O4 nanoparticles were encapsulated in the core, which resulted in magnetic core-shell hybrid particles by the same strategy. These particles have potential applications in biomolecular separation and high-temperature catalysis and as nanoreactors.

Vanadium pentoxide/carbide-derived carbon core–shell hybrid particles for high performance electrochemical energy storage

V2O5/carbide-derived carbon core–shell hybrid electrodes can be synthesized using vanadium carbide as the precursor. The resulting hybrid material shows high energy and power ratings for electrochemical energy storage.

Impact of speciation on the electron charge transfer properties of nanodiamond drug carriers.

Unpassivated diamond nanoparticles (bucky-diamonds) exhibit a unique surface reconstruction involving graphitization of certain crystal facets, giving rise to hybrid core-shell particles containing both aromatic and aliphatic carbon. Considerable effort is directed toward eliminating the aromatic shell, but persistent graphitization of subsequent subsurface-layers makes perdurable purification a challenge. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the impact of different fractions of aromatic and aliphatic carbon on the charge transfer properties of the ensembles of bucky-diamonds. By predicting quality factors for a variety of cases, we find that perfect purification is not necessary to preserve selectivity, and there is a clear motivation for purifying samples to improve the sensitivity of charge transfer reactions. This may prove useful in designing drug delivery systems where the release of (selected) drugs needs to be sensitive to specific conditions at the point of delivery.

Null Extinction of Ceria@silica Hybrid Particles: Transparent Polystyrene Composites.

Scattering of light in optical materials, particularly in composites based on transparent polymer and inorganic pigment nanoparticles, is a chronic problem. It might originate mainly from light scattering because of a refractive index mismatch between the particles and transparent polymer matrix. Thus, the intensity of light is rapidly diminished and optical transparency is reduced. Refractive index matching between the pigment core and the surrounding transparent matrix using a secondary component at the interface (shell) has recently appeared as a promising approach to alter light scattering. Here, CeO2 (ceria) nanoparticles with a diameter of 25 nm are coated with a SiO2 (silica) shell with various thicknesses in a range of 6.5-67.5 nm using the Stöber method. When the hybrid core-shell particles are dispersed into transparent polystyrene (PS), the transmission of the freestanding PS composite films increases over both the ultraviolet (UV) and visible region as the shell thickness increases particularly at 37.5 nm. The increase of transmission can be attributed to the reduction in the scattering coefficient of the hybrid particles. On the other hand, the particles in tetrahydrofuran (THF) absorb over UV and the intensity of absorption shows a systematic decrease as the shell thickness increases. Thus, the silica shell suppresses not only the scattering coefficient but also the molar absorptivity of the core ceria particles. The experimental results regarding the target shell thickness to develop low extinction (scattering + absorption) composites show a qualitative agreement with the predictions of Effective Medium Theory.

Synthesis and Characterization of Polymer-Based Magnetic Nanocomposite with Uniformly Distributed Hematite Nanoparticles on the Surface of Polystyrene Aromatic Compound

Nanosize hematite (α-Fe2O3) particles were synthesized by the Sol-gel method and were used for preparing polystyrene@α-Fe2O3 (PS@α-Fe2O3) nanocomposites via microemulsion polymerization by using ammonium proxidisulfate (APS) as an initiator. The obtained nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrophotometer, thermo gravimetric analysis (TGA), and vibrating sample magnetometer (VSM), respectively. TEM analysis showed that the average particle size of the α-Fe2O3 and PS@α-Fe2O3 nanocomposites synthesized were about 25 and 80 nm, respectively. The polystyrene microsphere was uniformly coated by α-Fe2O3 nanoparticles and the shell-thickness of the core-shell hybrid particles was controlled by the feed of α-Fe2O3 nanoparticles during the polymerization.

Synthesis and properties of fluorine–silicon modified polyacrylate hybrid latex particles with core–shell structure obtained via emulsifier‐free emulsion polymerization

AbstractA core–shell fluorine–silicon modified polyacrylate hybrid latex was successfully prepared via emulsifier‐free emulsion polymerization. The chemical composition and core–shell morphology of the resultant hybrid particles were investigated using 1H NMR and Fourier transform infrared spectroscopies and transmission electron microscopy (TEM), respectively. TEM analysis indicated that the core–shell hybrid particles were uniform with narrow size distributions. The particle size and zeta potential decreased with an increase of alkylvinylsulfonate surfactant from 2.5 to 6.0 wt%. X‐ray photoelectron spectroscopy revealed that fluorine concentrated preferentially at the film surface during a film‐formation process. The film formed from the fluorine–silicon modified polyacrylate showed much higher thermal stability than a film formed from polyacrylate and fluorine‐modified polyacrylate. Contact angle results showed that a finished fabric had remarkable water repellency. © 2015 Society of Chemical Industry

Atomic force microscopy indentation to determine mechanical property for polystyrene–silica core–shell hybrid particles with controlled shell thickness

The positively charged polystyrene (PS) particles with a size of ca. 200nm were synthesized by soap-free polymerization. The PS cores were coated with silica shells of tunable thickness employing the modified Stöber method. The PS cores were removed by thermal decomposition at 500°C, resulting in well-defined silica hollow spheres (10–30nm in shell thickness). The elastic response of the as-synthesized samples was probed by an atomic force microscope (AFM). A point load was applied to the particle surface through a sharp AFM tip, and the force–displacement curves were recorded. Elastic moduli (E) for the PS particles (2.01±0.70GPa) and the core–shell structured hybrid particles were determined on the basis of Hertzian contact model. The calculated E values of composites exhibited a linear dependence on the silica shell thickness. While the shell thickness increased from ca. 10 to 15 and 20nm, the E values of composites increased from 4.42±0.27 to 5.88±0.48 and 9.07±0.94GPa. For core–shell structured organic/inorganic composites, the E values of the hybrid particles were much lower than those of inorganic shells, while these values were much close to those of organic cores. Moreover, the moduli of elasticity of the composites appeared to be determined by the properties of the polymer cores, the species of inorganic shells and the thickness of shells. Besides, the inorganic shells enhanced the mechanical properties of the polymer cores. This work will provide essential experimental and theoretical basis for the design and application of core–shell structured organic/inorganic composite abrasives in chemical mechanical polishing/planarization.