Conventional and microwave-assisted synthesis of hyperbranched and highly branched polylysine towards amphiphilic core–shell nanocontainers for metal nanoparticles

Hyperbranched amphiphilic polymeric systems with core–shell architecture can be used as versatile nanocontainers and templates with great potential in application fields ranging from medicine to organic coatings. In order to explore an alternative to the already widely used and established synthetic macromolecules, we synthesized new polymers based on hyperbranched polylysine. Polylysine was prepared with classical heating and microwave-assisted heating, respectively. While, the synthesis at 160 °C resulted in hyperbranched polylysine with degrees of branching (DB) between 0.50 and 0.54, the microwave-assisted heating at 200 °C resulted in highly branched polymers with DB values of 0.30–0.32. The molecular weight M_n could be controlled in a range of 5000–12,000 g/mol. The hyperbranched polylysine was hydrophobized via polymer-analogue reactions using a mixture of stearoyl/palmitoyl chloride and glycidyl hexadecyl ether, respectively. These reactions yielded in high degrees of modification (80% and 90%, respectively). The synthesized polymers are soluble in non-polar organic solvents, such as toluene and chloroform, and take up metal salts to up to 25 wt.%. They support the formation of Ag, Au, and Pd nanoparticles and nanocrystals in organic solvents and stabilize them. Thus, the here presented macromolecules are a promising readily achievable alternative to existing core–shell systems.     

Synthesis and characterization of thermosensitive core–shell polymeric nanoparticles

Thermosensitive core–shell nanoparticles were synthesized by semicontinuous heterophase polymerization of styrene, followed by a seeded polymerization for forming a shell of poly(N-isopropyl acrylamide) (PNIPAM). Nanoparticles characterization by scanning transmission electronic microscopy showed core–shell morphology with average particle diameters around 40 nm. An inverse dependence of the particle size with temperature in the range 20–55 °C was identified by quasielastic light scattering measurements. As was expected for core–shell particles with PNIPAM as the shell, a volume phase transition near 32 °C was detected. In spite of thermosensitive properties of core–shell nanoparticles synthesized here, the volume percentage loss values were not so high, probably due to their relatively low content of PNIPAM.     

Waterborne polyurethane-acrylic copolymers crosslinked core–shell nanoparticles for humidity-sensitive coatings

A novel crosslinked core–shell emulsion of waterborne polyurethane-acrylic copolymers (PUA) was successfully synthesized by emulsion polymerization. The average particle size of the PUA particle was approximately 130 nm and its core–shell morphology was proved with transmission electron microscopy (TEM) and dynamic light scattering (DLS), whose structure was also confirmed by FT-IR and TGA. PUA was applied to prepare the humidity controlling coatings (PUA-C) by compositing with pigments and porous fillers. The structure and properties of humidity controlling coatings were investigated, with particular attention to the effects of the humidity controlling. The surface morphology of the PUA-C was observed by scanning electron microscope (SEM). The humidity controlling coatings showed excellent properties of humidity sensitivity and humidity retention.     

Preparation and characterization of CeOx@MnOx core–shell structure catalyst for catalytic oxidation of NO

The CeOx@MnOx catalyst with a core–shell structure was prepared and used for catalytic oxidation of NO. It was found that CeOx@MnOx catalyst showed higher intrinsic catalytic activity than CeMnOx catalyst prepared by citric acid method. Based on the characterization results of N₂ adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS), we may conclude that the excellent catalytic performance of CeOx@MnOx catalyst is related to its low crystallinity, good reducibility, and high concentrations of Mn^4 + and active oxygen species.     

Enhanced electrocatalytic activity and stability of PdCo@Pt core–shell nanoparticles for oxygen reduction reaction

The carbon-supported PdCo@Pt core–shell nanoparticles for an oxygen reduction reaction (ORR) were prepared via a two-step process at room temperature. The as-prepared PdCo@Pt/C with an average particle size of ~3.5 nm exhibited a well-defined nanostructure consisting of Pd-rich core and Pt shell formed by displacing Co core with Pt. Compared to pure Pt, PdCo@Pt/C showed a higher current density in the kinetic controlled region and more positive half-wave potential for the ORR. In a cycling stability test of the PdCo@Pt/C electrocatalyst, no remarkable activity loss was seen.     

Synthesis of superhydrophobic core–shell mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNPs) have been used in variety of applications due to their morphology and porous structure. This work reports the one-pot synthesis of ultrahydrophobic MSNPs using N-cetyl-n,n,n trimethyl ammonium bromide as a cationic surfactant template and ethanol (EtOH) as a cosolvent to form mesopores in the MSNPs. The effects of EtOH on the size and the pore structure of the MSNPs were studied by scanning electron microscopy and transmission electron microscopy. The results show that an addition of EtOH led to an enlargement of the MSNPs and a change in pore structure from a lamellar structure to a radially oriented structure. Co-condensation with two different types of fluoroalkyl silanes; trimethyl(fluoromethyl)silane, and trichloro(1H,1H,2H,2H-perfluorooctyl)silane provided low surface energy MSNPs with a core–shell structure. An assembly on the surface of these F-MSNPs generated nanostructure surface roughness rendering an improvement in surface wettability with water contact angle of 158.6°, which is a characteristic of oleophobic and ultrahydrophobic material.     

Viscoelasticity of shell-crosslinked core–shell nanoparticles filled polystyrene melt

Shell-crosslinked core–shell nanoparticles (SCCSN) of 63–104 nm in diameter and containing 79.1 wt% crosslinked polystyrene (PS) shell of 16.5–37.0 nm in thickness were prepared by miniemulsion polymerization of styrene in the presence of silane modified nanosilica. The PS shell was crosslinked using divinyl benzene in order to anchor the shell on the nanoparticle surface, to segregate the silica core from the matrix and to avoid entanglement between the shell PS and the matrix macromolecules in SCCSN filled PS composites. Steady and dynamic rheologies of SCCSN filled PS were compared with bare silica filled PS. The SCCSN filled PS composites exhibited exceedingly good rheological stability than silica filled ones during annealing. Both bare silica and SCCSN introduced a non-terminal dynamic rheology while they did not introduce additional mechanism responsible for origination of nonlinear steady flow except for macromolecular disentanglement of the PS matrix. The reinforcement of SCCSN to PS was related to the silica core even though the crosslinked shell could effectively eliminate filler aggregation as the case of silica filled PS.     

Preparation of superparamagnetic β-cyclodextrin-functionalized composite nanoparticles with core–shell structures

In this article, we report an original and feasible protocol for the preparation of superparamagnetic β-cyclodextrin-functionalized composite nanoparticles with core–shell structures via cross linking reaction on the surface of carboxymethyl β-cyclodextrin-modified magnetite (Fe₃O₄) nanoparticles by using epichlorohydrin as a crosslinking agent. The structure and morphology of the prepared composite nanoparticles were studied by Fourier transform infrared spectrometry, X-ray diffraction measurement, transmission electron microscopy and the thermogravimetric analysis. The results show that the prepared roughly spherical composite nanoparticles (diameter about 10–20 nm) with core–shell structures turned out to be magnetite nanoparticles surface-surrounded by a layer of cross-linked CM-β-cyclodextrin polymer. Results of vibrating sample magnetometry testing and inclusive behaviour studying confirmed the superparamagnetism with saturation magnetization value of 52.0 emu/g in an external applied magnetic field of 20000 Oe and inclusion functionality of the composite nanoparticles consisting of magnetite cores and β-cyclodextrin moiety, which implies very important applications in targeting drug delivery technology and separation for specific substances.     

Silicylacrylate copolymer core–shell emulsion for humidity coatings

Using silicylacrylate (SPMA: 3-(trimethoxysilyl)propyl methacrylate) and acrylic acid as functional monomers, silicylacrylate copolymer core–shell emulsion (SiA-CSE) was prepared by emulsion polymerization. The relationships between stability of SiA-CSE and contents of SPMA, emulsifier, initiator and copolymerization temperature were investigated. Moreover, the structure of SiA-CSE was characterized by FTIR, TEM and TGA techniques. The SiA-CSE was applied to prepare the silicylacrylate copolymer humidity coatings (SiA-CSE-C) by compositing with pigments and porous fillers. Based on measuring the basic performance of copolymer emulsion film and SiA-CSE coatings, the humidifying function of SiA-CSE coatings was investigated. In conclusion, SPMA could improve the adhesion of SiA-CSE film and water resistance of the coatings. The obtained coatings showed excellent humidity-sensitivity and humidity retention, which could be used as the interior walls coatings in the building.     

Comparison of film properties for crosslinked core–shell latexes

Thermosetting acrylic latexes were synthesized using butyl acrylate (BA), methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), and methacrylic acid (MAA) via seeded two-stage process. A 2-level factorial experimental design was employed to investigate the effect of hydroxyl (core phase), carboxylate (shell phase) groups, and type of surfactant (Triton X200, Tergitol XJ) on the mechanical properties of thermosetting latexes. Eight latexes with varying concentration of HEMA, MAA and two types of surfactants were synthesized and crosslinked with three crosslinkers. Latex functionality for crosslinking was located in the core only, the shell only, and both the core–shell with varying concentrations. Melamine-formaldehyde (hexamethoxymethyl melamine) resin was employed to crosslink hydroxyl functionalities in the core. Carboxylic acid groups in the shell were crosslinked with zinc ammonium carbonate. HDI isocyanurate (Desmodur N3300A) were used to crosslink with hydroxyl or carboxyl functional groups in core and shell. The mechanical properties of coatings were evaluated in terms of tensile properties, cross-hatch adhesion, pencil hardness, and impact resistance. Design of experiment (DOE) was utilized to investigate the effect of variables on mechanical properties of crosslinked thermoset films.     

Graphene supported Ru@Co core–shell nanoparticles as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane and methylamine borane

Well-dispersed graphene supported Ru@Co core–shell nanoparticles were synthesized by one-step in situ co-reduction of aqueous solution of ruthenium(III) chloride hydrate, cobalt(II) chloride hexahydrate and graphite oxide (GO) with ammonia borane under ambient condition. The as-synthesized nanoparticles exert excellent catalytic activities, with the turnover frequency (TOF) value of 344 mol H₂ min^− 1 (mol Ru)^− 1 for catalytic hydrolysis of ammonia borane, which is the second highest value ever reported. The as-synthesized catalysts exert superior catalytic activities than the monometallic (Ru/graphene), alloy (RuCo/graphene), and graphene-free Ru@Co counterparts towards the hydrolytic dehydrogenation of AB. Moreover, the catalytic hydrolysis of MeAB at room temperature was also studied. These Ru@Co NPs are a promising catalyst for amine-borane hydrolysis and for developing a highly efficient hydrogen storage system for fuel cell applications.     

Optimization of conditions for preparation of ZSM-5@silicalite-1 core–shell catalysts via hydrothermal synthesis

Although the preparation of ZSM-5@silicalite-1 (ZS) core-shell catalysts has been reported in the literature, their selectivity to para-xylene (PX) in the toluene alkylation with methanol is difficult to control. Here we present the effects of water and ZSM-5 adding amounts in the synthesis solution, the hydrothermal synthesis time, and the Si/Al ratio of core ZSM-5 on the catalytic performance of ZS core-shell catalysts. The ZS core-shell catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption, and NH₃ temperature-programmed desorption (NH₃-TPD) techniques. The highest PX selectivity of 95.5% was obtained for the ZS (Si/Al=140) catalyst prepared in the synthesis solution with a molar ratio of 0.2TPAOH:1TEOS:250H₂O at 175℃ and 10 r·min^-1 for only 2 h and the corresponding toluene conversion is as high as 22.8% for the alkylation of toluene with methanol.     

Facile synthesis of high-magnetization Fe3O4@polydivinylbenzene core–shell submicrospheres

Fe₃O₄@polydivinylbenzene (PDVB) submicrospheres were prepared via distillation–precipitation polymerization of DVB in the presence of submicron magnetite colloid nanocrystal clusters (MCNCs) as seeds. The surface of the MCNCs was modified with vinyl groups before PDVB encapsulation. The resulting Fe₃O₄@PDVB particles showed a well-defined core–shell structure, and the shell thickness could be readily controlled by the DVB dosage. A lowly cross-linked poly(methacrylic acid) (PMAA) layer could be further coated onto the highly cross-linked PDVB shell via a second-stage DPP process, suggesting the presence of residual vinyl groups on the surface of the Fe₃O₄@PDVB particles. The hybrid particles showed rather high magnetization and near superparamagnetism, hence capable of easy magnetic separation.     

Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate core based on amphiphilic block copolymers by RAFT polymerization and palladium-catalyzed coupling reactions

Well-defined amphiphilic block copolymers composed of S-vinyl sulfides and N-isopropyl acrylamide (NIPAM) were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Thermoresponsive core–shell nanoparticles with cross-linked π-conjugate cores were obtained by in situ cross-linking reactions between 4-bromophenyl moieties in the block copolymers and diboronic acids or a diamine compound in the presence of a palladium catalyst following micelle formation in ethanol/H₂O or ethanol. We initially investigated RAFT polymerization of two S-vinyl sulfide derivatives, namely phenyl vinyl sulfide (PVS) and 4-bromophenyl vinyl sulfide (BPVS), using a dithiocarbamate-type chain transfer agent (CTA). Then, RAFT polymerization of NIPAM using poly(S-vinyl sulfide) macro-CTAs was conducted to synthesize the amphiphilic block copolymers. Suzuki and Buchwald-Hartwig coupling reactions were found to be effective in the preparation of core–shell nanoparticles with thermoresponsive shells and cross-linked optoelectronic cores. The resulting nanoparticles showed characteristic thermoresponsive properties, as confirmed by turbidity and dynamic light scattering measurements. Stable and uniform core cross-linked nanoparticles were successfully prepared by the in situ palladium-catalyzed coupling reactions, and the optoelectronic and thermoresponsive properties of the nanoparticles could be tuned depending on the nature of the difunctional coupling agents, reaction conditions, and comonomer composition of the block copolymers.     

From core–shell and Janus structures to tricompartment submicron particles

Titanium dioxide nanoparticles are precisely segregated in or on polymer submicron particles domains by phase separation between a polymer and a hydrophobic liquid or between two different polymers. The inorganic nanoparticles can be located either in the core, as a patch on the surface of the polymer particle, as a disk, or in the middle of Janus polymer particles. In the latter case, tricompartment submicron particles arranged in a linear triblock fashion are fabricated.     

Preparation and properties of core–shell silver/polyimide nanocomposites

A new series of core–shell structured silver/polyimide (PI) nanocomposites was prepared by in situ polymerization followed by the chemical imidization of poly(amic acid) (PAA, precursor of PI) at a low temperature. The TEM images showed that the silver cores of the nanocomposites were encapsulated with homogeneous shells with thickness of 4 and 8 nm at silver contents of 90 and 60 %, respectively. The shell thickness was controlled by varying the content of PAA. FTIR spectroscopic analysis indicated that the imide ring formation occurred after the chemical imidization. The Ag/PI nanocomposites showed excellent thermal stability and exhibited only 10 % weight loss at 300 °C in the air. Moreover, percolation was observed at silver weight fractions close to the critical value, and the maximum dielectric permittivity of the nanocomposites was 120, which is about 40 times higher than that of pristine PI.     

Liquid–liquid equilibria for the ternary systems DMC–methanol–glycerol,DMC–glycerol carbonate–glycerol and the quaternary system DMC–methanol–glycerol carbonate–glycerol at catalytic reacting temperatures

Liquid–liquid equilibria of multicomponent systems involved in the synthesis of glycerol carbonate from dimethyl carbonate and glycerol were experimentally measured. Particularly, data for the ternary systems dimethyl carbonate + methanol + glycerol and dimethyl carbonate + glycerol carbonate + glycerol and the quaternary system dimethyl carbonate + methanol + glycerol carbonate + glycerol are provided at 333.2 K, 338.2 K and 343.2 K at atmospheric pressure since these temperatures prove relevant for the synthesis of carbonate glycerol from glycerol and dimethyl carbonate. The experimental data obtained were correlated with a good degree of agreement to the NRTL model in order to obtain the corresponding binary interaction parameters.     

Construction of site-specific core–shell structured nanocomposite for pH-controlled drug delivery

In this study, a pH-controlled core–shell structured site-specific magnetic nanocomposite for drug delivery was reported. Superparamagnetic Fe₃O₄ nanoparticles were selected to build its core for magnetic guiding purpose and mesoporous silica molecular sieve MCM-41 was chosen to construct its outer shell. The MCM-41 outer shell has highly ordered hexagonal tunnels therefore would offered enough cargo space for drug molecules. An organic ligand N1-(5H-cyclopenta[1,2-b:5,4-b′]dipyridin-5-ylidene)benzene-1,4-diamine (denoted as Dafo-Ph-NH₂) was linked to the molecular sieve outer shell. There are two nitrogen atoms at the end of the ligand which are able to donate their lone pair electrons. Acidic drug molecules therefore can be bound to the ligand via weak acid–base reaction. Those drug molecules can be release in low pH solution since the H⁺ in the solution will compete with the ligand. The final composite was analyzed by electron microscope images, XRD, IR spectra, thermogravimetry and N₂ adsorption/desorption. Its bio-compatibility was evaluated by MTT using L929 fibroblast cell line. Our Dafo-MCM-41@Fe₃O₄ composite shows pH-controlled and site-specific smart release properties for aspirin in vitro.     

Hierarchical NiO nanoflake coated CuO flower core–shell nanostructures for supercapacitor

In this work, we developed a simple and cost-effective approach to prepare the hierarchical NiO/CuO nanocomposite without any surfactant. The morphology and structure of the hybrid nanostructure was examined by focus ion beam scanning electron microscopy (FIB/SEM), X-ray diffraction spectroscopy (XRD) and high-resolution transmission electron microscopy (HRTEM). Furthermore, the electrochemical properties of the hierarchical NiO/CuO nanocomposite electrodes were elucidated by cyclic voltammograms, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in 6 M KOH electrolyte. The electrochemical results demonstrated that this unique NiO/CuO nanostructure exhibited a specific capacitance of 280 F g⁻¹ and excellent cycling stability (91.4% retention after 3000 cycles). The remarkable electrochemical performance coupled with the facile synthesis of the hierarchical NiO/CuO nanocomposite indicated the great application potential in supercapacitors.