Synthesis and surface properties of self-crosslinking core–shell acrylic copolymer emulsions containing fluorine/silicone in the shell

Stable emulsions of a core–shell acrylic copolymer (non-crosslinkable V0, and crosslinkable V2, V4, V6, and V8, where the numbers indicate the wt% of crosslinking agent based on the total acrylate monomer content) containing butyl acrylate (BA, 45 wt%), glycidyl methacrylate (GMA, 45 wt%), heptadecafluorodecyl methacrylate (PFA, 10 wt%), and various contents of crosslinking agent (vinyltriethoxysilane, VTES) were synthesized using a three-stage seeded emulsion polymerization process with a small amount of surfactant. The average particle size and viscosity of emulsions increased significantly with increasing VTES content. This study examined the effects of the VTES content on the surface/mechanical properties of self-crosslinked copolymer film samples containing a fixed acrylate monomer content to find the optimum VTES content. XPS showed that the film–air surface of the copolymer samples had a higher fluorine/silicone content than the film–dish interface. The tensile strength/modulus, thermal stability, and two Tgs (α and β Tgs) of the film samples increased significantly with increasing VTES content. The contact angle of the film samples increased with increasing VTES content up to approximately 6 wt%, and then decreased slightly. The optimum VTES content was approximately 6 wt% based on the total acrylate monomer content to obtain a high water/oil repellent coating material (V6) with the highest water/methylene iodide-contact angles (118.2°/81.8°) and lowest surface energy (18.4 mN/m).     

Synthesis of bifunctional core–shell particles with a porous zeolite core and a responsive polymeric shell

The aim of our work is the synthesis and characterization of colloidal core–shell particles with a zeolite core and an environmentally responsive shell. We have synthesized colloidal ZSM-5 zeolite and modified the surface with 3-(trimethoxysilyl)propyl methacrylate in order to introduce double bonds at the surface. The cross-linked polymeric shell was prepared by precipitation polymerization using the functionalized zeolite particles as seeds. We employed thermoresponsive poly(N-isopropylacrylamide) and pH-responsive poly(vinylpyridine) as the polymeric shell, respectively. The temperature- and pH-depending swelling and deswelling of the core–shell particles were characterized with dynamic light scattering techniques. Transmission electron microscopy pictures show the morphology of the synthesized particles. It is proposed that these types of bifunctional core–shell particles could be of use for controlled uptake and release applications and separation of molecules.     

How does the first water shell fold proteins so fast?

First shells of hydration and bulk solvent play a crucial role in the folding of proteins. Here, the role of water in the dynamics of proteins has been investigated using a theoretical protein-solvent model and a statistical physics approach. We formulate a hydration model where the hydrogen bonds between water molecules pertaining to the first shell of the protein conformation may be either mainly formed or broken. At thermal equilibrium, hydrogen bonds are formed at low temperature and are broken at high temperature. To explore the solvent effect, we follow the folding of a large sampling of protein chains, using a master-equation evolution. The dynamics shows a clear mechanism. Above the glass-transition temperature, a large ratio of chains fold very rapidly into the native structure irrespective of the temperature, following pathways of high transition rates through structures surrounded by the solvent with broken hydrogen bonds. Although these states have an infinitesimal probability, they act as strong dynamical attractors and fast folding proceeds along these routes rather than pathways with small transition rates between configurations of much higher equilibrium probabilities. At a given low temperature, a broad jump in the folding times is observed. Below this glass temperature, the pathways where hydrogen bonds are mainly formed become those of highest rates although with conformational changes of huge relaxation times. The present results reveal that folding obeys a double-funnel mechanism.     

K shell,L shell–subshell and M shell–subshell photoeffect cross-sections in elements between Tb (Z=65) and U (Z=92) at 123.6 keV

In this paper, we report on measurements of K shell, L shell–subshell and M shell–subshell photoeffect cross-sections for 21 high-atomic-number elements between Tb (Z=65) and U (Z=92) at 123.6 keV. These photoeffect cross-sections have been measured by using our earlier measurements of the K-shell X-ray production cross-sections. The measured photoeffect cross-sections have been compared with calculated theoretical values. It is clear that the results compare well with theoretical values within an experimental average error. At 123.6 keV, these cross-sections have been measured for the first time. The results have been plotted versus atomic number.     

Preparation of pH- and thermo-sensitive chitosan-PNIPAAm core–shell nanoparticles and evaluation as drug carriers

Environmentally sensitive polysaccharide nanoparticles (NPs) were prepared by in situ polymerization of N-isopropylacrylamide (NIPAAm) monomer in the presence of chitosan (CS) micelles. First, CS was found to develop a cationic micelle-like structure in the acetic acid solution when its concentration was increased to above the critical micelle concentration, as evidenced by fluorescence and TEM. When the NIPAAm was polymerized in the CS micelle solution by using potassium persulfate as initiator, the produced PNIPAAm with anionic chain end(s) became hydrophobic, as long as the reaction temperature was above its phase transition temperature; and therefore it would diffuse into the hydrophobic core of the CS micelles, producing CS-PNIPAAm core–shell NPs. Increasing the feeding amount of NIPAAm increased the monomer conversion and therefore the particle size; yet it decreased the surface zeta potential. Moreover, the CS-PNIPAAm NPs were sensitive to both pH value and temperature. For the study of drug release properties, doxycycline hyclate was used as a model drug and loaded into the NPs at pH 4.5 and 25 °C. The result illustrated that these NPs had a continuous drug release behavior up to 1 week, depending on the pH value and temperature. In addition, enzyme or hydrogen peroxide capable of degrading CS shell was added in the solution to facilitate the drug release.     

The dielectric response of interfacial water—from the ordered structures to the single hydrated shell

Water is the universal solvent in nature. Does this imply, however, that its interaction with its environment is also a universal feature? While this question maybe too fundamental to be answered by one method only, we present evidence that the broadening of the dielectric spectra of water presents universal features of dipolar interactions with different types of matrixes. If in aqueous solutions the starting point of water’s state can be considered as bulk, with only partial interactions with the solute, then the state of water adsorbed in heterogeneous materials is determined by various hydration centers of the inhomogeneous material (the matrix) and it is significantly different from the bulk. In both cases, the dielectric spectrum of water is symmetrical and can be described by the Cole–Cole (CC) function. The phenomenological model that describes a physical mechanism of the dipole–matrix interaction in complex systems underlying the CC behavior has been applied to water adsorbed in porous glasses. It was then extended to analyses of the dynamic and structural behavior of water in nonionic and ionic aqueous solutions. The same model is then used to analyze the CC relaxation processes observed in clays, aqueous solutions of nucleotides, and amino acids.     

Preparation of titania hollow particles with independently controlled void size and shell thickness by catalytic templating core–shell polymer particles

Organic/inorganic hybrids were prepared by catalytic hydrolysis and subsequent polycondensation of tetra-n-butyl titanate (TnBT) in shell layers grafted on core particles. The core particles were synthesized by emulsifier-free emulsion polymerization of styrene, N-n-butyl-N-2-methacryloyloxyethyl-N,N-dimethylammonium bromide (C₄DMAEMA), and 2-chloropropionyloxyethyl methacrylate using 2,2′-azobis(2-amidinopropane) dihydrochloride as an initiator. The core diameters were controlled in the range of 70–550 nm by adjusting a C₄DMAEMA feed concentration. The core–shell particles were prepared by surface-initiated activator generated electron transfer–atom transfer radical polymerization of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA). The sizes of core–shell particles were found to increase monotonically with an increase in a DMAEMA concentration. The hybrid particles were fabricated by adding TnBT into a water/ethanol dispersion of core–shell particles. The amounts of titania deposited increased in proportion to the grafted amounts of poly[2-(N,N-dimethylamino)ethyl methacrylate] on the core particles. The X-ray diffraction measurement revealed that the hollow titania particles obtained by heat treatment of hybrids have an anatase crystallographic phase.     

Synthesis and characterization of amino-functionalized single magnetic core–silica shell composites

The thermal decomposition approach, reverse micro-emulsion system and surface modification technique had been successfully used to synthesis single magnetic core Fe₃O₄@Organic Layer@SiO₂–NH₂ complex microspheres. The magnetization of the magnetic microspheres core could be easily tuned between 28 and 56 emu/g by adjusting the amount of 2-mercaptobarbituric acid. It was found that the Organic Layer to some extent had a protective effect on avoiding Fe₃O₄ being oxidized into Fe₂O₃. Each Fe₃O₄@Organic Layer microsphere could be coated uniformly by about 30 nm of silica shell. The average diameter of the Fe₃O₄@Organic Layer@SiO₂ composites was about 538 nm. The saturation magnetization of the Fe₃O₄@Organic Layer@SiO₂ complex microspheres was 12.5% less than magnetic microspheres cores. The Fe₃O₄@Organic Layer@SiO₂–NH₂ composites possessed a huge application potentiality in specificity enriching and separating biological samples.     

Can we understand the different coordinations and structures of closed‐shell metal cation‐water clusters?

We present a model potential for studying M(q+)(H(2)O)(n=1,9) clusters where M stands for either Na(+), Cs(+), Ca(2+), Ba(2+), or La(3+). The potential energy surfaces (PES) are explored by the Monte Carlo growth method. The results for the most significant equilibrium structures of the PES as well as for energetics are favorably compared to the best ab initio calculations found in the literature and to experimental results. Most of these complexes have a different coordination number in cluster compared to experimental results in solution or solid phase. An interpretation of the coordination number in clusters is given. In order to well describe the transition between the first hydration sphere and the second one we show that an autocoherent treatment of the electric field is necessary to correctly deal with polarization effects. We also explore the influence of the cation properties (charge, size, and polarizability) on both structures and coordination number in clusters, as well as the meaning of the second hydration sphere. Such an approach shows that the leading term in the interaction energy for a molecule in the second hydration sphere is an electrostatic attraction to the cation and not a hydrogen bond with the water molecules in the first hydration sphere.     

Preparation of thermoresponsive core–shell polymeric microspheres and hollow PNIPAM microgels

A reliable and efficient route for preparing thermoresponsive hollow microgels based on cross-linked poly(N-isopropyl acrylamide) (PNIPAM) was developed. Firstly, monodisperse thermoresponsive core–shell microspheres composed of a P(styrene (St)-co-NIPAM) core and a cross-linked PNIPAM shell were prepared by seeded emulsion polymerization using P(St-co-NIPAM) particles as seeds. The size of the P(St-co-NIPAM) core can be conveniently tuned by different dosages of sodium dodecyl sulfate. The thickness of the cross-linked PNIPAM shell can be controlled by varying the dosage of NIPAM in the preparation of PNIAPM shell. Then, hollow PNIPAM microgels were obtained by simply dissolving the P(St-co-NIPAM) core with tetrahydrofuran. The core–shell microspheres and the hollow microgels were characterized by transmission electron microscopy, dynamic light scattering, atomic force microscopy, and Fourier-transform infrared spectroscopy.     

Metalizing carbon nanotubes with Pd–Pt core–shell nanowires enhances electrocatalytic activity and stability in the oxygen reduction reaction

We describe an electrostatically induced self-assembly method to prepare ultrathin Pd nanowires (NWs) surrounding individual multiwalled carbon nanotubes, i.e., Pd_NW/MWNTs, that are noticeable for improving performance in the oxygen reduction reaction (ORR) of their supported Pt_ML electrocatalyst. The carbonaceous by-products in MWNTs, rather than the nanotubes themselves, are modified with the oxygenated terminals to allow the negatively charged and hydrophilic surface while retaining the intrinsic nature of the MWNTs. Encompassing the nanotubes' length are 2-nm-thick Pd NWs that are closely packed and homogeneously dispersed due to the unique processes for preparing Pd_NW/MWNTs and its components. Although the crystal lattice of the Pd NWs expands somewhat, which should cause an unfavorable interaction with supported Pt_ML, this adverse effect is counterweighed by the shape-determined features of Pd NWs, including their high specific surface area, excellent contiguousness, and low-energy atomic configuration. Consequently, these distinct chemical and physical properties substantially expedite the desorption of the intermediates to refresh the active centers during the reduction of oxygen with the Pt_ML electrocatalyst while ensuring a desirable electron transfer rate, so improving the overall ORR kinetics. Indeed, Pt_ML/Pd_NW/MWNTs exhibits the Pt mass and specific activities of 1.45 A/mg_Pt and 0.65 mA/cm² _Pt, respectively, each of which are several times those of the Pt/C and even higher than those of the Pt_ML supported on Pd nanoparticles. These high activities remained over a long-term stability test using the latest US Department of Energy-established protocol.     

Nanosized Pd assembled on superparamagnetic core–shell microspheres:Synthesis,characterization and recyclable catalytic properties for the Heck reaction

A series of magnetically recyclable Pd/Fe3O4@g-Al2O3 catalysts were synthesized using the superparamagnetic Fe3O4@g-Al2O3core–shell microspheres as the supporter and nano-Pd particles assembled on g-Al2O3 shell as the active catalytic component.The structure of the catalysts was characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),N2adsorption–desorption and vibrating sample magnetometer(VSM).The catalytic activity and the recyclability properties of the catalysts for the Heck coupling reaction with aryl bromides and the olefins were investigated.The results show that the microspheres of the magnetic Pd/Fe3O4@g-Al2O3 catalysts were about 400 nm and the nano-Pd particles assembled on g-Al2O3 shell were about 3–4 nm in size.The saturation magnetization(MS) of the magnetic catalysts was sufficiently high to allow magnetic separations.In the Heck coupling reactions,the magnetic Pd/Fe3O4@g-Al2O3 catalysts exhibited good catalytic activity and recyclability.With Pd/Fe3O4@g-Al2O3(0.021 mol%) catalyst,the bromobenzene conversion and product yield reached about 96.8% and 91.2%,respectively,at 120 8C and in 14 h.After being recycled for six times,the conversion of bromobenzene and the recovery of the catalyst were about80% and 90%,respectively.The nano-Pd particles were kept well dispersed in the used Pd/Fe3O4@g-Al2O3 catalysts.     

Synthesis and magnetic properties of the γ-Fe2O3/poly-(methyl methacrylate)-core/shell nanoparticles

The synthesis of γ-Fe₂O₃/poly-(methyl methacrylate)-core/shell nanoparticles and their magnetic properties are reported. Specific γ-Fe₂O₃ nanoparticles capable of initiating atom transfer radical polymerization (ATRP) were prepared by a ligand exchange reaction of ((chloromethyl)phenylethyl)-dimethylchlorosilane and caprylate-capped γ-Fe₂O₃ nanoparticles of 4 nm in diameter, and the ATRP of methyl methacrylate was carried out subsequently. These nanoparticles were characterized with Fourier transform infrared spectroscopy, transmission electron microscopy and Mössbauer spectroscopy. Low temperature magnetic properties investigated with SQUID magnetometry revealed that the coercivity and the blocking temperature changed slightly owing to surface effects.     

Some practical comparisons of the efficiency and overloading behaviour of sub-2 μm porous and sub-3 μm shell particles in reversed-phase liquid chromatography

At their optimum flow, sub-3 μm superficially porous or "shell" particles demonstrate similar efficiency to sub-2 μm totally porous particles. The performance of 0.21 cm i.d shell columns is however inferior to those of 0.46 cm i.d., presumably due to packing difficulties. At high flow, shell columns can give flatter Knox curves due to lower operating pressure (half or less of that of the totally porous particles) producing less frictional heating, which combined with the increased thermal conductivity of their non-porous core, gives more efficient heat dissipation. However, the effects of frictional heating for sub-2 μm columns are considerably exaggerated when using pure ACN as mobile phase, as it has a thermal conductivity 3 times less than that of pure water, leading to poorer heat dissipation. Overloading is already problematic for ionised solutes, a group which contains many pharmaceuticals and compounds of clinical relevance, on conventional columns (5 μm porous particles). However, it becomes a more serious issue for both new column types, partially as a result of their very high efficiency, which concentrates the sample as a very narrow band. The sample capacity of one type of shell particle was estimated to be 60% of that of the small totally porous particles, in line with the fraction of the particle volume that is porous. Due to overloading, it is barely possible to achieve perfect peak symmetry for ionised acids or bases with either of these new column types, even by injecting the lowest amounts of sample detectable by UV. While ammonium formate and potassium phosphate buffers gave similar results in overloading studies, use of formic acid as sole mobile phase additive is not recommended for these solutes, as its ionic strength is too low, leading to a catastrophic deterioration in efficiency when sample concentrations of even a few mg/L are injected.     

A core–shell structured BaTiO3 precursor preparation,characterization and potential

A new procedure for the preparation of a core-shell-structured BaTiO(3) precursor (core=TiO(2); shell=BaCO(3)) will be described. The structure of this precursor is characterized by electron microscopy (environmental scanning electron microscopy; energy disperse X-ray spectroscopy), whereas the development of phases during thermal treatment is followed by X-ray powder diffraction.     

Electrochemical preparation and characterization of magnetic core–shell nanowires for biomedical applications

Magnetic CoNi@Au core–shell nanorods have been electrochemically synthesized, characterized and functionalized to test their inherent cytotoxicity in order to assess their potential use for biomedical applications. The initially electrodeposited CoNi nanorods have been covered with a gold layer by means of galvanic displacement to minimize the nanowires toxicity and their aggregation, and favour the functionalization. The presence of a gold layer on the nanorod surface slightly modifies the magnetic behaviour of the as-deposited nanorods, maintaining their soft-magnetic behaviour and high magnetization of saturation. The complete covering of the nanorods with the gold shell favours a good functionalization with a layer of (11-Mercaptoundecyl)hexa(ethylene glycol) molecules, in order to create a hydrophilic coating to avoid the aggregation of nanorods, keeping them in suspension and give them stability in biological media. The presence of the organic layer incorporated was detected by means of electrochemical probe experiments. A cytotoxicity test of functionalized core–shell nanorods, carried out with adherent HeLa cells, showed that cell viability was higher than 80% for amounts of nanorods up to 10 μg mL^− 1. These results make functionalized nanorods promising vehicles for targeted drug delivery in medicine, which gives a complementary property to the magnetic nanoparticles.     

Amphiphilic polymeric particles with core–shell nanostructures: emulsion-based syntheses and potential applications

The design and synthesis of amphiphilic nano- to micro-sized polymeric particles with core–shell nanostructures have attracted more and more attention because of their wide applicability in modern material science and their technological importance in the areas of colloid and interface science. Many synthetic strategies have been developed for the preparation of amphiphilic core–shell particles that consist of hydrophobic polymer cores and hydrophilic polymeric shells. In this review, we focus on emulsion-based approaches and properties of particles produced. These methods are: (1) grafting to functionalized particle that produces a corona-like particle, (2) grafting from reactive seed particle that produces a brush-like particle, (3) copolymerization of reactive macro-monomer with hydrophobic monomer that produces a corona-like particle, (4) emulsion polymerization in the presence of block or comb-like copolymer containing controlled free-radical moiety that produces a multi-layered particle, and (5) redox-initiated graft polymerization of vinyl monomer from a water-soluble polymer containing amino groups that produces a hairy-like particle. Potential applications of some of these particles in drug and gene deliveries, enzyme immobilization, colloidal nanocatalyst, chemical sensing, smart coating, and thermal laser imaging will be discussed.     

Electrochemical determination of the surface composition of Pd–Pt core–shell nanoparticles

Different amounts of Pt atoms were deposited onto the surface of Pd nanoparticles supported on carbon black by hydroquinone reduction method in anhydrous ethanol. Here, we surveyed electrochemical probing of surface compositions of Pd–Pt surface alloys. They were calculated from hydrogen desorption, carbon monoxide adlayer oxidation, and reduced carbon dioxide oxidation charges. The surface composition of Pt drastically increased up to Pt[0.3]/Pd/C (23.1 at.% of Pt) and then approached that of pure Pt with the moderate rate of increase.     

Polyelectrolyte microcapsules containing molecules of sulfated β-cyclodextrin in the structure of nanosized shell

Alternate adsorption of the molecules of poly(allylamine hydrochloride) (PAA) and sulfated β-cyclodextrin (sulfo-β-CD) is studied by piezoelectric microweighing upon the formation of coatings of nanosized thicknesses by the polyionic assembly procedure. The thickness of planar coatings on the surface of single-crystalline silicon is determined by ellipsometry. The layer-by-layer character of the formation of planar nanosized coating is revealed and assumptions about the structure of the PAA and sulfo-β-CD bilayers are stated. A comparison of the spherical microparticles of polystyrene, as well as manganese and calcium carbonates, demonstrated that it is feasible to use microparticles of calcium carbonate as a template for producing microcapsules. Microcapsules with shells containing five (PAA/sulfo-β-CD) layers are prepared and studied by confocal fluorescent microscopy.     

Core–shell nanoparticles of carboxy methyl cellulose and compritol-PEG for antiretroviral drug delivery

Multi-functional nanoparticles hold great promise for the effective treatment of many diseases. Zidovudine a commonly used anti-HIV drug, requires a delivery system for more effective treatment of AIDS. The present study focuses on the development of anti-viral drug-loaded hybrid nanoparticles (LPNs) of lipid and polymer consisting of carboxy methyl cellulose—zidovudine (AZT) core enclosed by a compritol (Comp)-polyethylene glycol shell. The characterization of drug loaded LPNs was done using TEM, DLS and FT-IR analysis. The drug loading efficiency, drug release, blood compatibility, MTT assay and cell uptake studies were carried out using the LPNs. The synthesized nanoparticles exhibited core–shell morphology with an average size of 161.65 ± 44.06 nm; the LPN also demonstrated 82% drug encapsulation efficiency with slow drug release behaviour. The hybrid nanoparticles were found to be blood compatible and non toxic. The rhodamine-labeled hybrid nanoparticles were also found to effectively enter the brain cells. The novel hybrid drug delivery system shows controlled drug release, biocompatibility and high drug loading efficiency. These LPNs obtained from natural polymers can provide an excellent platform for designing systems for targeted drug delivery.