Effect of microwave irradiation on crystalline structure and dielectric property of PVDF/PZT composite

The crystalline structure change and dielectric performance of microwave-irradiated PVDF/PZT composites were studied by FTIR, DSC, DMTA, and DEA. The dielectric analysis suggests that the dielectric permissivity and loss reduce, which is useful for improving the sensitivity of composites used in passive transducers. The structure analysis results show that the microwave irradiation promotes crystalline transformation of PVDF from α to β; The crystallinity of PVDF in PVDF/PZT composites increases and ΔT decreases; the DMTA measurements illustrate that the value of E′ and tanδ peak increases after irradiation.     

Polypropylene/SiO<Subscript>2</Subscript> nanocomposites filled with different nanosilicas: thermal and mechanical properties,morphology and interphase characterization

Untreated and surface-treated SiO₂ nanoparticles with different alkyl chain length (described as C0, 3C1, C8 and C16 according to the number of carbon atoms) on particle surface were used as fillers for isotactic polypropylene (iPP). The iPP/SiO₂ composites containing 2.3 vol% of nanoparticles were prepared by melt blending and injection moulding. The dispersion quality of nanoparticles in matrix was examined using scanning electron microscopy (SEM). The crystallization behaviour of iPP was examined using differential scanning calorimetry (DSC). The mechanical properties of all samples were characterized by tensile test, compact tension (CT) test and dynamic mechanical thermal analysis (DMTA). The particle–matrix interphase behaviour was also examined and discussed. SEM images show that different silicas show different dispersion quality in matrix due to different hydrophobicity. The crystallinity and spherulite size of matrix are overall decreased in composites. The tensile properties of iPP/SiO₂ composites show clear relationship with alkyl chain length on particle surface, i.e. increasing alkyl chain length leads to decreased tensile modulus but increased tensile yield strength and strain, indicating increased interfacial interactions with increased alkyl chain length. The 3C1-composite shows the highest fracture toughness with an improvement by 9% compared to neat iPP, whereas the other composites show decreased values of fracture toughness.     

Evaluation of residual strains in epoxy with different nano/micro-fillers using embedded fiber Bragg grating sensor

The influence of SiO₂ nanoparticles and rubber micro-fillers on the mechanical and thermal responses of an epoxy based composite is investigated using classical quantitative thermo-mechanical testing (tensile tests, DMTA, TMA), microstructural analysis (Micro-CT, TEM, SEM microscopy) as well as distributed optical sensing in order to determine different residual strain fields generated during processing. The results show that the tensile modulus of the compounds increases with the addition of SiO₂ and decreases with the rubber content, following estimates of the Hashin–Shtrikman model. The coefficient of thermal expansion appears to be insensitive to the particles’ content in the temperature range investigated. The residual strains generated during processing are influenced by the rubber content that introduces a strong relief, with respect to the one generated by the neat resin, whereas the silica content tends to increase their level.     

Poly(vinylidene fluoride)/poly(methyl methacrylate)/TiO2 blown films: preparation and surface study

Blown films of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) blends and PVDF/PMMA/TiO₂ composites were prepared by melting-extrusion for the first time. The crystalline structure and surface morphology PVDF/PMMA (DFMA) blown films were investigated using differential scanning calorimeter (DSC), atomic force microscope (AFM), and X-ray diffractometry (XRD). PVDF/PMMA/TiO₂ blown films were further prepared and underwent surface treatment. The results show that PVDF/PMMA/TiO₂ blown films present good mechanical properties, and acrylic acid surface-grafted films exhibit good adhesion capability and long-lasting hydrophilicity, making them attractive as encapsulation materials.     

Preparation and investigation of PVDF/PMMA/TiO2 composite film

Polyvinylidene fluoride (PVDF)/Polymethylmethacrylate (PMMA)/Titanium dioxide (TiO₂) composite, and its films was prepared and studied in detail. The structure, morphology, crystalline behavior, thermal, and mechanical properties of PVDF/PMMA/TiO₂ film were investigated through FT-IR/ATR, SEM, XRD, DSC, TGA, and Py-GC/MS, respectively. The results showed that the blended material and its film have favorable thermal and mechanical properties. The TiO₂ particles finely dispersed in the composite featured by crystalline regions of PVDF and homogeneous amorphous regions consisted of PVDF and PMMA, resulting in an advantageous properties and improvement of tensile strength and elongation at break of the PVDF/PMMA film. However, the TiO₂ can greatly narrow the thermally stable margin of PVDF in PVDF/PMMA/TiO₂ composite for at least 100 °C with catalysis decomposition effect.     

Characterization of Poly (ethylene terephthalate)/SiO2 nanocomposites prepared by Sol–Gel method

Poly (ethylene terephthalate) (PET)/SiO₂ nanocomposites were synthesized via the Sol–Gel method that involves two steps: terephthalic acid was first reacted with excess ethylene glycol to form bis (hydroxyethyl) terephthalate (BHET); then the tetraethoxysilane (TEOS) were transferred to the BHET followed by the Sol–Gel reactions at high temperature to form silica nanonetworks concurrent with polycondensation of BHET to produce the PET matrix. Transmission electron microscopy (TEM) showed that silica particle size was at nanoscale, and the nanoparticles were uniformly dispersed in the polymer matrix. Thermogravimetric analysis (TGA) results indicated that the activation energy of thermal degradation of the composites was largely improved. The flame retardancy of the composites was found to be improved according to cone calorimeter (CONE). The nonisothermal crystallization ability of the composites was found to be depressed according to differential scanning calorimetry (DSC).     

Preparation and performance of silica/polypropylene composite separator for lithium-ion batteries

In an effort to improve thermal stability and mechanical properties of porous polypropylene (PP) separators for lithium-ion battery, SiO₂/PP/SiO₂ composite separators were prepared by introducing SiO₂ layer on both sides of PP separator through a dip-coating process, with polyvinylidene fluoride–hexafluoropropylene (PVDF–HFP) as binder. SiO₂ nanoparticles are evenly distributed and closely packed in the coated layer, which features a porous honeycomb structure. This unique porous structure was quantitatively analyzed by Gurley value, and it can retain liquid electrolyte, leading to higher electrolyte uptake and ionic conductivity of the composite separator. The introduction of SiO₂-coated layers can not only suppress thermal shrinkage but also improve mechanical properties of the composite separator. C-rate capability and cycle performance of composite separator were also investigated, and compared to those of pristine PP separator.     

Synthesis of silver-integrated silica nanostructures using rice hulls and their electrochemical performance for supercapacitor application

We report the synthesis of silver-integrated silica nanostructures using rice hulls and silver chloride through a facile thermal combustion process. The formation of mesoporous silica nanomatrix embedded with silver nanoparticles (SiO₂:Ag 5 wt% and SiO₂:Ag 10 wt%) was confirmed by XRD, FTIR, EDX, BET, and TEM analysis. Also, the obtained results from the above studies revealed that the concentration of silver ions significantly increases the particle size and number of silver nanoparticles formed in the silica matrix. The electrochemical performance was studied using silver-integrated silica nanostructures as a working electrode in KOH electrolyte. The maximum specific capacitance of SiO₂:Ag 5 wt%- and SiO₂:Ag 10 wt%-coated electrode was found to be 517 and 580 F/g at current density of 1 A/g. It was also found that SiO₂:Ag 10 wt% electrode exhibit an excellent stability with the capacitance retention of 94% than SiO₂:Ag 5 wt% (capacitance retention of 85%) after 1000 cycles at a current density of 1 A/g. These results may be attributed to the inherent characteristic of more silver nanoparticles present in the silica nanomatrix in SiO₂:Ag 10 wt%. The intrinsic characteristic of rice hull-derived silica nanostructures such as high surface area and mesoporous structure along with the advantage of silver nanoparticles (conductivity) can facilitate the Faradic redox processes at electrode surface which are responsible for the supercapacitive behavior of the prepared silver-integrated silica nanostructures.

     

Swelling properties and bioactivity of silica gel/pHEMA nanocomposites

A novel hydrogel based on 2-hydroxyethyl- methacrilate and SiO₂ nanoparticles was prepared. The filler was added at a concentration of 30% w/w of silica nanoparticles to the mass of polymer. The composite material was characterised as far as concerns swelling behaviour in comparison to pHEMA. Swelling ratio of modified pHEMA was higher. Bioactivity of both SiO₂ nanoparticles and the modified hydrogel was evaluated by soaking samples into a simulated body fluid (SBF). FT-IR spectroscopy, scanning electron microscopy (SEM) and energy dispersive system (EDS) results suggest silica nanoparticles keep bioactive in the polymer. SiO₂ filler in a p(HEMA) matrix makes the composite bioactive. Therefore, these composites can be used to make bioactive scaffold for bone engineering.     

可分散性纳米二氧化硅增强硅橡胶

采用表面经过硅烷偶联剂原位修饰的纳米二氧化硅增强硅橡胶。通过扫描电子显微镜和Payne 效应考察了纳米二氧化硅在硅橡胶中的分散特性; 用DSC 分析了复合体系的低温结晶行为; 考察了填料对硅橡胶力学性能的影响。结果表明, 由于修饰后纳米颗粒表面非极性有机基团的存在和表面能的降低, 无须加入分散剂, 纳米颗粒就能在硅橡胶中有较好的分散; 在各自最优添加量时, DNS-3 链状纳米二氧化硅增强的硅橡胶相对于气相法二氧化硅增强的硅橡胶在拉伸强度、撕裂强度及断裂伸长率上有显著提高; DNS-2 纳米二氧化硅增强性能与气相法二氧化硅的相当, 但前者混炼胶黏度较小, 有较好的加工性。      

Diatom Frustules Decorated with Co Nanoparticles for the Advanced Anode of Li-Ion Batteries

Silica is regarded as a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity. However, large volume variation and poor electrical conductivity are limiting factors for the development of SiO₂ anode materials. To solve this problem, combining SiO₂ with a conductive phase and designing hollow porous structures are effective ways. In this work, The Co(II)-EDTA chelate on the surface of diatom biosilica (DBS) frustules and obtained DBS@C-Co composites decorated with Co nanoparticles by calcination without a reducing atmosphere is first precipitated. The unique three-dimensional structure of diatom frustules provides enough space for the volume change of silica during lithiation/delithiation. Co nanoparticles effectively improve the electrical conductivity and electrochemical activity of silica. Through the synergistic effect of the hollow porous structure, carbon layer and Co nanoparticles, the DBS@C-Co-60 composite delivers a high reversible capacity of >620 mAh g⁻¹ at 100 mA g⁻¹ after 270 cycles. This study provides a new method for the synthesis of metal/silica composites and an opportunity for the development of natural resources as advanced active materials for LIBs.     

Tunable BT@SiO2 core@shell filler reinforced polymer composite with high breakdown strength and release energy density

Barium titanate@silicon dioxide (BT@SiO₂) core@shell fillers with an average diameter of 100 nm were prepared by a facile sol–gel synthesis. The thickness of SiO₂ shell can be easily tuned by varying different mass ratio of BT to tetraethyl orthosilicate (TEOS). Polyvinylidene fluoride (PVDF) based composite films reinforced by BT and BT@SiO₂ were fabricated via a solution casting method. The effects of SiO₂ shell on morphology structure, wettability, interfacial adhesion, dielectric, electrical and energy performances of composites were investigated. Compared with BT/PVDF, BT@SiO₂/PVDF composites show significantly increased breakdown strength due to enhanced interfacial adhesion and suppressed charge carrier conduction. Benefiting from enhanced breakdown strength and reduced remnant polarization induced by SiO₂ shell, BT@SiO₂/PVDF shows increased release energy density (energy density which can be fully discharged and applicable). Especially, BT@SiO₂/PVDF with SiO₂ thickness of 4 nm exhibits the highest release energy density of 1.08 J/cm³ under applied electric field of 145 kV/mm.     

Engineering a High-Selectivity PVDF Hollow-Fiber Membrane for Cesium Removal

In this study, a copper ferrocyanide/silica/polyvinylidene fluoride (CuFC/SiO₂/PVDF) hollow-fiber composite membrane was successfully synthesized through a facile and effective crosslinking strategy. The PVDF hollow-fiber membrane with embedded SiO₂ was used to fix the dispersion of CuFC nanoparticles for cesium (Cs) removal. The surface morphology and chemical composition of the composite membrane were analyzed using scanning electron microscopy and X-ray photoelectron spectroscopy (XPS). The composite membrane showed a high Cs rejection rate and membrane flux at the three layers of CuFC and 0.5% SiO₂, and its Cs rejection rate was not affected by variation in the pH (pH = 4–10). The modified membrane could be effectively regenerated many times using ammonium nitrate (NH₄NO₃). The Cs selectivity performance was verified by an efficient Cs rejection rate (76.25% and 88.67% in 8 h) in a solution of 100 μg·L⁻¹ of Cs with 1 mmol·L⁻¹ of competing cations (K⁺ and Na⁺). The CuFC/SiO₂/PVDF hollow-fiber composite membrane showed a particularly superior removal performance (greater than 90%) in natural surface water and simulated water with a low Cs concentration. Therefore, the CuFC/SiO₂/PVDF hollow-fiber composite membrane can be used directly in engineering applications for the remediation of radioactive Cs-contaminated water.     

Carbon-loaded porous composites produced by matrix carbonization of poly(vinylidene fluoride)

Using poly(vinylidene fluoride) (PVDF) carbonization at 750° C in fine-particle silica and its mixtures with graphite, we have prepared carbon-loaded porous composites which offer benzene absorption from 0.90 to 1.52 ml/g, compressive strength of 6 MPa, and Brinell hardness of up to 18 MPa. We observed the formation of various nanostructures (spheres, spherical segments, and layered platelets) and sizes (several to hundred nanometers). X-ray photoelectron and energy dispersive x-ray spectroscopy data indicate the presence of C-C, C =C, CO, COO, and CHF groups on the carbon surface. X-ray emission spectroscopy data show that the silica matrix composite prepared via PVDF carbonization contains small carbon clusters weakly bonded to the matrix. The silica/graphite matrix composite contains multilayer carbon films strongly bonded to the matrix. The OK _α spectra of both composites are similar to the spectrum of pure SiO₂.     

Fabrication and characterization of three dimensional woven carbon fiber/silica ceramic matrix composites

Carbon fiber reinforced fused silica composites exhibit the advantages of excellent mechanical properties, high heat resistance, low thermal expansion and low density, but low impact resistance or toughness. A novel modified slurry impregnation and hot pressing (SIHP) method was adopted to fabricate a new type of three dimensional orthogonal woven structure carbon fiber reinforced silica ceramic matrix composites (3D Cf/SiO₂ CMCs) with higher density and lower porosity. Physical characterization, flexural behavior, impact performance and toughening mechanism of the composites were investigated by three-point bending tests, impact tests, and scanning electron microscopy analysis. The 3D Cf/SiO₂ CMC showed a higher flexural strength in both warp (201.6%) and weft (263.6%) directions than those of pure SiO₂ and failed at a non-brittle mode due to the fiber debonding and pullout, and a delaminated failure of the 3D preform. The maximum impact energy absorption of the 3D Cf/SiO₂ CMC was 96.9 kJ/m², almost 4 times as much as those for typical other carbon fiber reinforced CMCs.     

Improvements in transmittance,mechanical properties and thermal stability of silica–polyimide composite films by a novel sol–gel route

Sol–gel process has been frequently employed for preparation of silica/polyimide composite films. In this article, a novel sol–gel route is introduced to prepare silica (SiO₂)/polyimide (PI) (PS2 system) composite films and to enhance the compatibility between the polyimide and silica. The transmittance, mechanical properties, thermal stability, and morphology of the PS2 composites are studied and compared with the PS1 films prepared by the traditional sol–gel route. The results show that the transmittance, mechanical properties and thermal stability of the PS2 composites are significantly improved especially at high silica contents when compared with those of their counterparts prepared by the traditional sol–gel route. This is explained in terms of the silica particle size and dispersion in the two composites. In addition, the effect of silica particle size on the thermal expansion of silica/PI films is also examined.     

Self-assembled natural rubber/silica nanocomposites: Its preparation and characterization

A novel natural rubber/silica (NR/SiO₂) nanocomposite is developed by combining self-assembly and latex-compounding techniques. The results show that the SiO₂ nanoparticles are homogenously distributed throughout NR matrix as nano-clusters with an average size ranged from 60 to 150 nm when the SiO₂ loading is less than 6.5 wt%. At low SiO₂ contents (4.0 wt%), the NR latex (NRL) and SiO₂ particles are assembled as a core-shell structure by employing poly (diallyldimethylammonium chloride) (PDDA) as an inter-medium, and only primary aggregations of SiO₂ are observed. When more SiO₂ is loaded, secondary aggregations of SiO₂ nanoparticles are gradually generated, and the size of SiO₂ cluster dramatically increases. The thermal/thermooxidative resistance and mechanical properties of NR/SiO₂ nanocomposites are compared to the NR host. The nanocomposites, particularly when the SiO₂ nanoparticles are uniformly dispersed, possess significantly enhanced thermal resistance and mechanical properties, which are strongly depended on the morphology of nanocomposites. The NR/SiO₂ has great potential to manufacture medical protective products with high performances.     

Multiscale reinforcement and interfacial strengthening on epoxy-based composites by silica nanoparticle-multiwalled carbon nanotube complex

The multiscale reinforcement and interfacial strengthening on epoxy-based composites by nanoscale complex composed of zero-dimensional silica nanoparticles (SiO₂) and one-dimensional multiwalled carbon nanotubes (MWCNTs) was examined. The SiO₂–MWCNT complex was successfully prepared by multi-step functionalization, which was characterized with FTIR, XPS and TEM. Mechanical properties of epoxy (EP) composites were significantly enhanced by SiO₂–MWCNTs rather than other functionalized MWCNTs, due to synergy reinforcing effect of MWCNTs and SiO₂ as well as enlarged interfacial areas by SiO₂. The chemically bonded nanoscale interfacial area between glass fiber and matrix was generated and bridged by SiO₂–MWCNTs, making glass fiber like a branched reinforcement, resulting in strong interfacial adhesion and effective stress transfer. Mechanical properties of SiO₂–MWCNT/EP composites and GF/SiO₂–MWCNT/EP composites were even higher than those predicted by Halpin–Tsai model and rule of mixtures, resulting from strengthened interfacial adhesion in the composites, high chemical reactivity of SiO₂–MWCNTs and additional reinforcing effect of SiO₂.     

Dielectric and magnetic properties of ferrite/poly(vinylidene fluoride) nanocomposites

Particulate composite films of poly(vinylidene fluoride) and CoFe₂O₄ and NiFe₂O₄ were prepared by solvent casting and melt processing. The well-dispersed ferrite nanoparticles nucleate the piezoelectric β-phase of the polymer, but the different ferrites nucleate the whole polymer crystalline phase at different filler concentrations. The macroscopic magnetic and dielectric response of the composites demonstrates a strong dependence on the volume fraction of ferrite nanoparticles, with both magnetization and dielectric constant increasing for increasing filler content. The β-relaxation in the composite samples is similar to the one observed for β-PVDF obtained by stretching. A superparamagnetic behavior was observed for NiFe₂O₄/PVDF composites, whereas CoFe₂O₄/PVDF samples developed a hysteresis cycle with coercivity of 0.3 T.     

Characterization of di-phasic nanoscale composites derived from xerogels

Di-phasic xerogel-derived composites, such as SiO₂AgCl, SiO₂-AIPO₄, SiO₂-CePO₄, SiO₂ -Nd₂O₃, SiO₂-CdS, SiO₂CrPO₄, SiO₂-BaSO₄ and SiO₂-PbCrO₄ have been characterized in detail by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED) techniques. The SiO₂-AgCl photochromic composites with small amounts of AgCl did not show any crystallinity either by XRD or by SAED. Thin edges of these SiO₂-AgCl composites did not reveal discrete AgCl particles because these are too small to be resolved even by TEM and are expected to be in the range 1.5 to 2.5 nm in size based on the pore size of silica gel. A few large AgCI-Ag particles precipitated on the outside of silica gel were, however, detected by TEM-SAED in silica gels with higher concentrations of AgCl. The SiO₂-AIPO₄ and SiO₂-Nd₂O₃ composites are noncrystalline and did not show any periodic structure by TEM and SAED. Heat treatments to 400 or 600° C did not crystallize the AIPO₄ or Nd₂O₃ phases. On the other hand, SiO₂-CePO₄ and SiO₂-CdS composites showed lath-like particles of CePO₄ and irregular particles of presumably CdS on the surfaces of silica gels. The SiO₂-BaSO₄ and SiO₂-PbCrO₄ composites showed crystals of BaSO₄ and PbCrO₄ which are too large to be incorporated in the silica gel pores. These results show that the size and crystallinity of a second phase within silica gels can be controlled by the appropriate manipulation of the different parameters, and to do so is an important advantage for this new class of diphasic nanoscale composite xerogel materials.