Suspension polymerization based on inverse Pickering emulsion droplets for thermo-sensitive hybrid microcapsules with tunable supracolloidal structures

Polymerization using Pickering emulsion droplets as reaction vessels is being developed to become a powerful tool for fabrication of hybrid polymer particles with supracolloidal structures. In this paper, two kinds of thermo-sensitive hybrid poly(N-isopropylacrylamide) (PNIPAm) microcapsules with supracolloidal structures were successfully prepared from suspension polymerization stabilized by SiO₂ nanoparticles based on inverse Pickering emulsion droplets. SiO₂ nanoparticles could self-assemble at liquid-liquid interfaces to form stable water-in-oil inverse Pickering emulsion. NIPAm monomers dissolving in suspended aqueous droplets were subsequently polymerized at different temperatures. The hollow microcapsules with SiO₂/PNIPAm nanocomposite shells were obtained when the reaction temperature was above the lower critical solution temperature (LCST) of PNIPAm. While the core-shell microcapsules with SiO₂ nanoparticles' shells and PNIPAm gel cores were produced when the polymerization was conducted at the temperature lower than LCST using UV light radiation. The supracolloidal structures with different cores could be tuned by simply changing reaction temperature, which was confirmed by confocal laser scanning microscopy and scanning electron microscopy. The interesting properties of both microcapsules were their ability of reversibly swelling during drying/wetting cycles and responsive to temperature stimulus. Such functional microcapsules may find applications in double control release system due to the presence of the supracolloidal structures and thermo-sensitivity.     

Ionic Liquid‐Coated Nickel Phosphide Catalysts for Selective Hydrodesulfurization

Ni₂P/SiO₂ catalysts were coated with the ionic liquid (IL) 1‐butyl‐3‐methylimidazolium bis[(trifluoromethyl)sulfonyl]amide with different coating thicknesses and their selective hydrodesulfurization performances were investigated using a model fluid catalytic cracking gasoline. The selective factor on the IL‐coated catalysts (IL‐Ni₂P/SiO₂) first increased and then decreased as the initial mass ratio of IL to Ni₂P/SiO₂ catalyst ranged from 0.02 to 0.18. A maximum selectivity factor of 16.7 was found at a mass ratio of 0.10 which corresponds to full monolayer coverage on the original Ni₂P/SiO₂ catalyst by the IL. In comparison, the selectivity factor was 6.7 for the Ni₂P/SiO₂ catalyst, indicating a significant selectivity improvement by the IL coating method.     

Phase Separation and Spatial Morphology in Sodium Silicate Glasses by AFM,Light Scattering and NMR

The morphological and structural properties of sodium silicate (Na₂O–SiO₂) glasses were analyzed using atomic force microscopy (AFM) and light scattering following thermal treatments. AFM observations indicated that the glass surface microstructure evolves during the phase separation mechanisms from continuous interpenetrating phases in the spinodal decomposition process to separated droplets embedded in a continuous matrix for the nucleation/growth one. Raman mapping gave evidence of a phase separation through the nucleation/growth process with formation of silica‐rich clusters characterized by higher polymerization degree as separate droplets. The variations in inhomogeneities versus temperature investigated by Brillouin are exponential for spinodal decomposition and linear in the case of nucleation/growth mechanism. Nuclear magnetic resonance spectroscopy was used to investigate the spatial distribution of the various Q_n species present in thermally treated glasses and allows determining fractal dimension between two and three.     

Retarded relaxation and breakup of deformed PA6 droplets filled with nanosilica in PS matrix during annealing

The effect of hydrophilic silica nanoparticles (SiO₂) on the relaxation and breakup dynamics of selectively filled polyamide (PA6) droplets with different degrees of deformation in polystyrene (PS) matrix during quiescent annealing were in situ investigated. It was found that, with the increase of silica content, the relaxation process of PA6 droplets was slowed down gradually and the relaxation mode was changed correspondingly. The critical break aspect ratios (AR_cr) of PA6 droplets were also improved with the increase in SiO₂ nanoparticle contents. Comparisons of the experimental values of AR_cr, characteristic relaxation time (τ_d) and breakup time (t_b) of the SiO₂-filled PA6 droplets with corresponding theoretical values were made. The results of comparison were discussed in terms of viscoelasticity and interfacial tension. It was proposed that the alternation of the viscoelastic properties of PA6 droplets in stead of the interfacial tension change of the blends was responsible for the phenomena observed.     

Novel polyacrylonitrile nanocomposites containing Na-montmorillonite and nano SiO2 particle

Polyacrylonitrile (PAN)/Na-montmorillonite (Na-MMT)/SiO₂ nanocomposites were prepared via in situ emulsion polymerization. X-ray diffraction (XRD) results suggest that the Na-MMT layers are exfoliated during the polymerization process. As evidenced by the transmission electron microscope (TEM), the Na-MMT and nano SiO₂ particles exhibit good dispersion in the polymer matrix. It was found that the PAN/Na-MMT/SiO₂ nanocomposites exhibit considerably enhanced mechanical properties compared with the PAN/Na-MMT and PAN/SiO₂ nanocomposites.     

Synthesis of 100 μm uniform porous spheres by SPG emulsification with subsequent swelling of the droplets

100 μm porous p(styrene-co-divinylbenzene) (PS-DVB) microspheres were synthesized by employing a particular membrane emulsification technique, and subsequent swelling of the seed droplets. DVB dissolving a water-insoluble substance, hexadecane (HD), and an initiator was permeated through a SPG (Shirasu porous glass) membrane, and the uniform (seed) droplets were released to a stabilizer solution acting as the continuous phase. The average droplet size was around 30 μm, and this emulsion was mixed with a secondary emulsion of much smaller size consisting of more hydrophilic components, a mixture of styrene, middle chain alcohol (C6 to C8), dichlorobenzene, and isoamyl acetate, which promotes the degradative diffusion process of the components. After all the droplets in the secondary emulsion virtually disappeared, the seed droplets were swollen to a maximum 110 μm. Polymerization was carried out at 348 K under a nitrogen atmosphere. Uniform porous spheres of 100 μm with the coefficient of variation less than 10% were obtained. Specific surface area was 350 m²/g. Careful controlling of the specific gravity of swollen droplets and the choice of solvents balancing between the good solvency for the polymer and polarity (solubility in water) proved vital in order that the polymerization may proceed without an extensive phase separation in the early stage, which eventually induces breakup of the droplets. The three component system, isoamyl acetate-hexanol-o-dichlorobenzene, provided an adequate cosolvent for these purposes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 931–942, 1997     

Thermal properties of single-phase Y2SiO5

Y₂SiO₅ is a promising candidate for oxidation-resistant or environmental/thermal barrier coatings (ETBC) due to its excellent high-temperature stability, low elastic modulus and low oxygen permeability. In this paper, we investigated the thermal properties of Y₂SiO₅ comprehensively, including thermal expansion, thermal diffusivity, heat capacity and thermal conductivity. It is interesting that Y₂SiO₅ has a very low thermal conductivity (～1.40 W/m K) but a relatively high linear thermal expansion coefficient ((8.36 ± 0.5) × 10^?6 K^?1), suggesting compatible thermal and mechanical properties to some non-oxide ceramics and nickel superalloys as ETBC layer. Y₂SiO₅ is also an ideal EBC on YSZ TBC layer due to their close thermal expansion coefficients. As a continuous source of Y³⁺, it is predicted that Y₂SiO₅ EBC may prolong the lifetime of zirconia-based TBC by stopping the degradation aroused by the loss of Y stabilizer.     

Zinc ion conducting blended polymer electrolytes based on room temperature ionic liquid and ceramic filler

Zinc ion conducting nanocomposite gel polymer electrolytes (NCGPEs) comprising of poly(vinyl chloride) (PVC)/poly(ethyl methacrylate) (PEMA) blend, zinc triflate [Zn(OTf)₂] salt, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) ionic liquid (IL) and fumed silica (SiO₂) viz. [PVC/PEMA–Zn(OTf)₂–EMIMTFSI–SiO₂] exhibited the highest ionic conductivity value of 6.71 × 10⁻⁴ Scm⁻¹ at room temperature. The ion–filler–polymer interactions and probable conformational changes observed in the structure of the gel composites due to the entrapment of IL and dispersion of nano-sized SiO₂ were confirmed from X-ray diffraction (XRD) and Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. Scanning electron microscopic (SEM) images of NCGPEs demonstrated uniform surface with abundant interconnected micropores. The cationic transport number of NCGPE samples has been found to be appreciably enhanced up to a maximum of 0.69 thus demonstrating a considerable improvement in Zn²⁺ ion conductivity. The NCGPE film possesses an electrochemical stability window up to 5.07 V (vs. Zn/Zn²⁺) and ensures feasible zinc stripping/plating in the redox process. The addition of SiO₂ into the gel polymer electrolyte system has effectively reduced the glass-transition temperature (T_g) of the NCGPE films and also accomplished improved thermal stability up to approximately 180 °C which were ascertained from Differential scanning calorimetry (DSC) and Thermogravimetric (TG) results. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47654.     

改性纳米SiO2/聚氨酯-含氟丙烯酸酯无皂乳液合成及其胶膜性能表征

引言水性聚氨酯相对溶剂型聚氨酯具有不燃、气味小、不污染环境等优点[1-2],从而广泛用于涂料[3]、胶黏剂[4]、油墨[5]等领域。目前,常用于软包装领域的薄膜主要是表面能很低的非极性膜,而水性聚氨酯胶黏剂具有较高的表面自由能,对非极性膜的润湿性差,因此需要降低水性聚氨酯的表面张力,达到润湿非极性膜的目的。     

Polyacrylate/silica hybrids prepared by emulsifier-free emulsion polymerization and the sol–gel process

Polyacrylate/silica hybrids were prepared by emulsifier-free emulsion polymerization and the sol–gel process. The influence on the properties of polyacrylate/silica hybrids of the synthetic conditions, such as the dosage of polyvinyl alcohol, the ratio of the monomers, the dosage of tetraethoxysilane and the dosage of γ-methacryloxypropyltrimethoxysilane, was investigated. The hybrid material was characterized by Fourier transform infrared, differential scanning calorimeter, thermal gravimetric analyzer and dynamic light scattering. The results indicated that there were chemical bonds between SiO₂ and polyacrylate, that the thermal stability and the average diameter of polyacrylate emulsion particle increased with the incorporation of SiO₂, and that the glass transition temperature (T _g) of polyacrylate/SiO₂ was 8 °C higher compared with that of pure polyacrylate.     

Infrared spectra of dinitrogen adsorbed on bimetallic lanthanide (Eu or Yb)–Ni/SiO2 catalysts

Bimetallic lanthanide (Ln: Eu or Yb)–Ni/SiO₂ catalysts prepared by the use of dissolution of lanthanide metals in liquid ammonia have been studied by infrared spectroscopy for dinitrogen adsorption. The infrared spectra were measured at 133–300 K using Ln–Ni/SiO₂ obtained when the Eu or Yb metal dissolved in liquid ammonia reacted with 20 mass% Ni/SiO₂ in different ratios. Infrared spectra for Eu–Ni/SiO₂ showed absorption bands at 2336, 2265, 2254 and 2227 cm⁻¹ at 133 K, which disappeared upon evacuation. The adsorbed state was found to be all molecular from the isotope shift using ²⁸N₂ and z³⁰N₂₈. The bands at 2254 and 2227 cm⁻¹ of them were assigned to new adsorbed dinitrogen species resulting from synergetic interactions between the europium and nickel metal. The concentration of adsorbed dinitrogen on Eu–Ni/² varied markedly with the Eu/Ni ratios, and particularly, it increased in the region of high Eu content. Upon introduction of ytterbium onto nickel, new bands at 2254 and 2226 cm^−- similarly appeared. However, the dependence of dinitrogen adsorption as a function of Yb content in Yb–Ni/SiO²> was somewhat different from that for Eu–Ni/SiO₂. The effects of lanthanide on the surface of Ln–Ni/SiO₂ were discussed in connection with the variation in catalytic properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation and performance of nano‐SiO2 stabilized Pickering emulsion type sizing agent for glass fiber

The nano‐SiO₂ particles modified by silane coupling agent A‐1100 were used for preparing the vinyl ester resin (VE) Pickering emulsion. The stable emulsion could be served as the film former of sizing agent for glass fiber (GF). The influence of the wettability and the addition amount of nano‐SiO₂ on the stability of film former emulsion was explored. The effect of nano‐SiO₂ Pickering emulsion type sizing agent on the properties of GF was investigated. SEM images show that there existed a layer of sizing agent film with nano‐SiO₂ particles evenly on the GF surface. The abrasion resistance of the sized GF reached 3,579 times and the stiffness was 69 mm. The strand integrity also performed well. The fracture strength of GF bundles treated by Pickering emulsion type sizing agent increased by 28.6% to 0.504 N/Tex compared with that of the unsized GF bundles. The interlaminar shear strength (ILSS) of GF/VE composites sized by self‐made sizing agent which contained nano‐SiO₂ has improved, compared to the unsized GF reinforced VE composite. POLYM. COMPOS., 37:334–341, 2016. © 2014 Society of Plastics Engineers     

Stability of multiple emulsions under shear stress

Multiple liquid emulsions of the water in oil in water (W₁/O/W₂) type are used in a variety of consumer or technical applications, for instance in the encapsulation of certain active ingredients. The encapsulation process and release mechanisms of the inner phase of the carrier drops are important in order to properly process and formulate such liquid-liquid systems. In this work the stability and breakage of multiple W₁/O/W₂ emulsions under mechanical shear stress are investigated for emulsions with different surfactants and surfactant concentrations of the internal emulsion. Stressing the emulsions in a mechanical stirring process is compared to the membrane emulsification process. The membrane emulsification process results in higher encapsulation efficiencies than the stirring process. The emulsion droplets were subjected to shear stress below and above the critical capillary number for drop breakup. The results show that stable inner emulsions with sufficient surfactant concentrations increase the overall encapsulation efficiency for multiple emulsions subjected to shear stress, although the effect is not prominent. The depletion of the carrier oil droplets could be achieved for Ca numbers below the critical limit, reducing the encapsulation efficiency below 10 %. This shows that even a low shear stress can result in content release from the internal droplet phase. The experimental emulsion release study is supported by a numerical simulation of drop deformation and break-up under shear stress.     

Preparation and characterization of PTFE-g-GMA modified PTFE/SiO<Subscript>2</Subscript> organic–inorganic hybrids

In this paper, PTFE (polytetrafluoroethylene)/SiO₂ organic–inorganic hybrids were prepared with PTFE emulsion and tetraethoxysilanes (TEOS) through in-situ Sol–gel process, and then modified by PTFE grafted polymer. The studies included Sol–gel manufacturing process, the effects of SiO₂ content and graft polymer on the properties of the hybrids. The result showed that, cosolvent ethanol was not needed during the process of Sol–gel because it could make PTFE emulsion colloidal particles agglomerated. When the mass fraction of SiO₂ was 1.05 %, the tensile strength reached 20.96 MPa, which was nearly twice as much as that of the pure PTFE sample. Hybrids were treated by PTFE grafted glycidyl methacrylate (PTFE-g-GMA) and silane coupling agent KH-550, after which the tensile properties of hybrids were all enhanced. SEM (scanning electron microscope) images showed that SiO₂ changed the original fracture morphology of PTFE. The diameter of SiO₂ could reach 110 nm in the hybrid, and the size of SiO₂ was further refined by modification. Hybrids with different contents of SiO₂ were also analyzed with TGA (thermogravimetric analyzer), through which it could be found that decomposition temperature were improved with an increasing SiO₂ content. Furthermore, the crystallinity reached a maximum value 47.03 % measured by DSC (different scanning calorimetry) when the SiO₂ content was 2.55 %. Additionally, more SiO₂ could hinder the motion of chain segment and destroy the crystallization sequence length, so the crystallinity and crystallization velocity both decreased at the mass fraction of 7.37 %, but the crystallization behavior was enhanced after modification with graft polymer. It has been found that PTFE-g-GMA contributes to the compatibility between PTFE and SiO₂.     

Preparation of poly(methyl methacrylate)‐Silica nanoparticles via differential microemulsion polymerization and physical properties of NR/PMMA‐SiO2 hybrid membranes

Poly(methy methacrylate) (PMMA)‐SiO₂ nanoparticles were prepared via differential microemulsion polymerization. The effects of silica loading, surfactant concentration, and initiator concentration on monomer conversion, particle size, particle size distribution, grafting efficiency, and silica encapsulation efficiency were investigated. A high monomer conversion of 99.9% and PMMA‐SiO₂ nanoparticles with a size range of 30 to 50 nm were obtained at a low surfactant concentration of 5.34 wt% based on monomer. PMMA‐SiO₂ nanoparticles showed spherical particles with a core‐shell morphology by TEM micrographs. A nanocomposite membrane from natural rubber (NR) and PMMA‐SiO₂ emulsion was studied for mechanical and thermal properties and pervaporation of water‐ethanol mixtures. PMMA‐SiO₂ nanoparticles which were uniformly dispersed in NR matrix, significantly enhanced mechanical properties and showed high water selectivity in permeate flux. Thus, the NR/PMMA‐SiO₂ hybrid membranes have great potential for pervaporation process in membrane applications. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers     

Modification of polyethylene–octene elastomer by silica through a sol–gel process

In this study, tetraethoxysilane (TEOS) and a metallocene polyethylene–octene elastomer (POE) were chosen as the ceramic precursor and the continuous phase, respectively, for the preparation of new hybrids by an in situ sol–gel process. To obtain a better hybrid, a maleic anhydride‐grafted polyethylene–octene elastomer (POE‐g‐MAH), used as the continuous phase, was also investigated. Characterizations of POE‐g‐MAH/SiO₂ and POE/SiO₂ hybrids were performed by Fourier transform infrared (FTIR) and ²⁹Si solid‐state nuclear magnetic resonance (NMR) spectrometers, a differential scanning calorimeter (DSC), a thermogravimetry analyzer, and an Instron mechanical tester. The results showed that the POE‐g‐MAH/SiO₂ hybrid could improve the properties of the POE/SiO₂ hybrid because the interfacial force between the polymer matrix and the silica network was changed from hydrogen bonds into covalent Si? O? C bonds through dehydration of hydroxy groups in POE‐g‐MAH with residual silanol groups in the silica network. The existence of covalent Si? O? C bonds was proved by FTIR spectra. For the POE/SiO₂ and POE‐g‐MAH/SiO₂ hybrids, maximum values of the tensile strength and the glass transition temperature were found at 9 wt % SiO₂ since a limited content of silica might be linked with the polymer chains through the covalent bond. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 966–972, 2003     

Improved dispersion and interfacial interaction of SiO2@polydopamine fillers in polytetrafluoroethylene composites for reduced thermal expansion and suppressed dielectric deterioration

Copper-clad laminate (CCL) comprised of copper foil and polytetrafluoroethylene (PTFE) faces severe thermal expansion mismatch due to the discrepancy in coefficient of thermal expansion (CTE) between the two components. Incorporating inorganic fillers with low CTE into PTFE has been proved to be a promising way to achieve the goal. However, it is a challenge to achieve homogeneous distribution and good interfacial interaction of fillers in PTFE composites owing to the characteristics of PTFE emulsion. In this work, core@shell structured SiO₂@polydopamine fillers (SiO₂@PDA) were synthesized and incorporated into PTFE matrix to form SiO₂@PDA/PTFE composites. Due to the presence of PDA shell, SiO₂@PDA exhibited improved dispersion and interfacial interaction, contributing to the reduced CTE and suppressed dielectric deterioration of SiO₂@PDA/PTFE composites. With 40 vol% of filler, the CTE of SiO₂@PDA/PTFE composite was efficiently reduced (50%), coupled with a limited sacrifice of only 2% and 40% of increments for dielectric constant (D_k, 2.3) and dielectric loss (D_f, 2.4 × 10⁻³), respectively (@40 GHz), as compared with that of the corresponding SiO₂/PTFE composite. The fillers and composites were comprehensively characterized to verify the mechanism of CTE and dielectric properties of the composites.     

Preparation of styrene‐acrylic emulsion by using nano‐SiO2 as seeds

A styrene‐acrylic/SiO₂ nanoparticle composite emulsion was prepared by using SiO₂ nanoparticles as seeds. The effect of factors such as the level of nano‐SiO₂, reaction temperature and ultrasound treatment of nano‐SiO₂ on the stability of the polymerization reaction was investigated. Water‐resistance of the emulsion was measured. The level of nano‐SiO₂ in the emulsion was determined by inductively coupled plasma (ICP) spectrometry. The particle morphology of the emulsion with nano‐SiO₂ was observed with transmission electron microscopy (TEM). The kinetics of the polymerization was also studied at various temperatures and various levels of nano‐SiO₂. They showed that the level of nano‐SiO₂ and reaction temperature had a great influence on the monomer conversion, particle size, coagulum content and viscosity of the emulsion. Nano‐SiO₂ treated by ultrasonics can increase the coagulum content greatly, but it does not improve the water resistance of the emulsion. The level of nano‐SiO₂ in the emulsion was lower than the theoretical value. The reaction kinetics indicated that the level of nano‐SiO₂ had less influence on the reaction rate than the reaction temperature. Even a small amount of nano‐SiO₂ can decrease the reaction rate. Copyright © 2004 Society of Chemical Industry     

Effective removal of Fe(II) impurity from rare earth solution using surface imprinted polymer

Rare earth is a very important resource. But, impurities, such as Fe²⁺, have great influence on the properties of rare earth material. In this paper, a novel Fe²⁺-ionic imprinted polyamine functionalized silica gel adsorbent was prepared by a surface imprinting technique for selective adsorption of Fe²⁺ from rare earth solution. Firstly, functional macromolecule polyethyleneimine (PEI) was grafted onto the surfaces of silica gel particles, and the PEI/SiO₂ was formed. Secondly, the ionic imprinting process was carried out using Fe²⁺ ion as a template, and Cr³⁺ ionic imprinting polyamine IIP-PEI/SiO₂ was prepared. The adsorption and recognition properties of IIP-PEI/SiO₂ for Fe²⁺ were studied in detail, and the effects of main imprinting conditions, such as the amount of crosslinking agent and reaction time, on the adsorption property of the imprinted material IIP-PEI/SiO₂ were examined. The experimental results showed that the IIP-PEI/SiO₂ possesses strong adsorption affinity, specific recognition ability, and excellent selectivity for Fe²⁺. The adsorption capacity could reach to 0.334 mmol g⁻¹, and relative selectivity coefficients to Pr³⁺ and Ce³⁺ are 23.25 and 18.42, respectively. Besides, the IIP-PEI/SiO₂ was regenerated easily using diluted hydrochloric acid solution as eluent and IIP-PEI/SiO₂ possesses better reusability.     

Fabrication of covalently-bonded polystyrene/SiO<Subscript>2</Subscript> composites by Pickering emulsion polymerization

Pickering emulsion polymerization has attracted considerable attention in material fabrication due to its unique surfactant-free character and versatile association of oil, water and particles for a large set of materials. In this study, SiO₂ modified with Methacryloxypropyltrimethoxysilane (MPTMS) was employed to prepare Pickering emulsion, and subsequently covalently-bonded polystyrene/SiO₂(PS/SiO₂) composites were synthesized by Oil-in-water Pickering emulsion polymerization. Optical micrograph, contact angle, thermogravimetric analysis (TGA), Fourier transform infrared spectra (FT-IR), scanning electron microscope (SEM) and dynamic laser scattering (DLS) were employed to characterize the modified SiO₂, Pickering emulsion and prepared composites. It was found that prepared composites possess ragged surface morphology and SiO₂ concentration has an important effect on the morphology of as-prepared composites. In addition, covalent bond between PS core and SiO₂ shell was evidenced by FT-IR.