Swift heavy ion induced ordering and piezoelectric β-phase in poly(vinylidene fluoride)

Ion flux dependent swift heavy ions (SHI) induced structural changes have been reported for pristine poly(vinylidene fluoride) (PVDF). Ordering phenomena has been observed first followed by its transformation from α to β-form (polar metastable piezoelectric phase). The ordering of (020) plane become prominent at higher ion flux SHI irradiation and its further increase induces structural change from α to β phase as revealed by XRD and FTIR analyses. Structural changes are also supported by morphological evidence and thermal studies before and after SHI irradiation.     

Composition-dependent physical properties of poly[(vinylidene fluoride)-co-trifluoroethylene]–poly(ethylene oxide) blends

Polymer blends based on poly(vinylidene fluoride-co-trifluoroethylene) copolymers, P(VDF-TrFE), and poly(ethylene oxide), PEO, with varying compositions have been prepared by solvent casting. In this way, P(VDF-TrFE) crystallizes from the solution while solvent evaporates, while PEO crystallizes from the melt during cooling to room temperature. The surface morphology of the polymer blends indicates the transition from the fibrillar microstructure typical of PVDF-TrFE to the spherulite structure characteristic of PEO. The vibration mode characteristics of P(VDF-TrFE) are not influenced by the presence of PEO in the polymer blend. Confinement of PEO in the P(VDF-TrFE) phase change the conformation of PEO from trans to helix, increasing this transformation for increasing P(VDF-TrFE) content in the polymer blends. Sequential crystallization of the two polymers produce separated amorphous phases whose independent cooperative conformational motions are revealed by two main dynamic-mechanical relaxations. No chemical interaction seems to exist between the polymers within the blend.     

Enhanced dielectric permittivity and breakdown strength of poly(vinylidene fluoride) nanocomposites containing core–shell BaTiO3@TiO2 nanofibers

Journal of Materials Science: Materials in Electronics - Dielectric capacitor has been rapidly developed in recent years, and the ceramics nanofibers/polymer nanocomposites with improved dielectric...     

Isothermal crystallization kinetics of poly(vinylidene fluoride) in the α-phase in the scope of the Avrami equation

Isothermal melt crystallization of poly(vinylidene fluoride) (PVDF) at different crystallization temperatures was studied by differential scanning calorimetry. Analysis by the two different approaches of the Avrami equation was performed: first the classical double logarithmic approximation was used, but a non-linear least squares search showed to clearly improve the fit of the model to the experimental isotherms. The differences found by both methods in the Avrami parameters are discussed. The limitation of the Avrami equation in this polymer has to do not only with the fitting procedure to determine the parameters but also with the lack of a consistent physical interpretation of their temperature evolution. The melting behavior of the samples was analyzed and an equilibrium melting temperature of 190.9 °C was obtained by the Hoffmann–Weeks extrapolation. The samples crystallize in a spherulitic structure, as observed by optical microscopy with polarized light (OMPL). Lauritzen–Hoffmann theory was applied to analyze the crystallization kinetics and the Regime III was found for the crystallization of α-PVDF.     

Piezoelectric and pyroelectric properties of (Bi0.5Na0.5)0.94Ba0.06TiO3/P(VDF-TrFE) 0–3 composites

Bismuth sodium barium titanate [(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ or BNBT] ceramic powder have been incorporated into a polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE) 70/30 mol%] copolymer matrix to form 0–3 composites. With the composition near the MPB region, BNBT has relatively high piezoelectric and dielectric properties. P(VDF-TrFE) ferroelectric copolymer films can be poled to give piezoelectric and pyroelectric performance without prior mechanical stretching. The composites were prepared using solvent casting to disperse the ceramic powder homogeneously in the copolymer matrix. Composites with BNBT volume fraction ϕ ranging from 0.05 to 0.30 were fabricated using a hot-press method. The piezoelectric and pyroelectric coefficients of the composites were studied as a function of ϕ under different poling conditions. As BNBT has a low relative permittivity, so it is relatively easy to pole the BNBT ceramic inclusion. Hence, the BNBT 0–3 composites were found to have better pyroelectric properties than that of the lead zirconate titante PZT/P(VDF-TrFE) 0–3 composites.     

Pt-Sn/Poly(triazine imide)-碳纳米管复合材料的电催化性能

以不同质量比poly(triazine imide)(PTI)-碳纳米管(carbon nanotubes, CNTs)复合物为载体,通过乙二醇还原Pt/Sn前驱体制备了Pt-Sn/PTI-CNTs催化剂。通过X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)对制备的催化剂结构、形貌和成分进行表征。结果表明,Pt-Sn纳米粒子在载体上高度分散,粒径分布在2.6～3.7 nm之间,其主要以金属Pt和SnO_x的形式存在。循环伏安(CV)测试表明,PTI的引入对Pt-Sn/PTI-CNTs复合物的催化活性具有明显提升作用,但是加入的量过多会导致电催化性能下降。当加入20%(质量分数)的PTI时,催化剂具有最大的电化学活性面积(ECSA)46.20 m~2/g,乙醇电催化性能最佳。     

Dielectric and Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3–PbTiO3–Pb(Mg1/2W1/2)O3 Ceramics

Data are presented on the phase composition, crystal structure, microstructure, and dielectric and piezoelectric properties of (1 – y)[(1 – x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃]–yPb(Mg_1/2W_1/2)O₃ (x = 0.30–0.36; y = 0, 0.05, 0.10) ceramics. It is shown that the use of fine-particle magnesia as a starting reagent ensures the formation of single-phase materials. The ceramics with a rhombohedral structure are found to exhibit relaxor behavior. Increasing the content of the Pb(Mg_1/2W_1/2)O₃ perovskite leads to ordering of the domain structure of poled ceramics and increases their piezoelectric charge coefficient d ₃₁ and the width of their phase transitions.     

Poly(ε-caprolactone)-based membranes with tunable physicochemical,bioactive and osteoinductive properties

In contrast to currently used materials, membranes for the treatment of bone defects should actively promote regeneration of bone tissue beyond their physical barrier function. What is more, both material properties and biological features of membranes should be easily adaptable to meet the needs of particular therapeutic applications. Therefore, the role of preparation methods (non-solvent-induced phase separation and thermal-induced phase separation) of poly(ε-caprolactone)-based membranes and their modification with gel-derived bioactive glass (BG) particles of two different sizes (<45 and <3 μm) in modulating material morphology, polymer matrix crystallinity, surface wettability, kinetics of in vitro bioactivity and also osteoblast response was investigated. Both surfaces of membranes were characterised in terms of their properties. Our results indicated a possibility to modulate microstructure (pore size ranging from submicron to hundreds of micrometres), wettability (from hydrophobic to fully wettable surface) and polymer crystallinity (from 19 to 60%) in a wide range by the use of various preparation methods and different BG particle sizes. Obtained composite membranes showed excellent in vitro hydroxyapatite forming ability after incubation in simulated body fluid. Here we demonstrated that bioactive layer formation on the surface of membranes occurred through ACP–OCP–CDHA–HCA transformation, that mimic in vivo bone biomineralization process. Composite membranes supported human osteoblast proliferation, stimulated cell differentiation and matrix mineralization. We proved that kinetics of bioactivity process and also osteoinductive properties of membranes can be easily modulated with the use of proposed variables. This brings new opportunities to obtain multifunctional membranes for bone regeneration with tunable physicochemical and biological properties.     

pH敏感性含糖共聚水凝胶Poly(AM/IA/VBG)的制备与性能

用4-乙烯基苄基胺与葡萄糖内酯反应合成了4-乙烯苄基葡萄糖酰胺单体(VBG)，然后以亚甲基双丙烯酰胺(BisA)为交联剂，与丙烯酰胺(AM)、衣康酸(IA)共聚得到含糖结构的三元共聚水凝胶。用热重分析对水凝胶的稳定性进行了表征。水凝胶的膨胀比随着VBG或IA含量的增加而下降；在低pH值或高pH值时水凝胶的膨胀比下降。随氯化钠浓度的提高，水凝胶的膨胀比下降。随着温度的升高水凝胶的膨胀比出现不同的变化，凝胶中VBG含量的增加，水凝胶的膨胀比随着温度的升高而下降，凝胶中IA含量的增加，水凝胶的膨胀比随着温度的升高反而升高。     

溶胶-凝胶法制备纳米TiO_2-ZrO_2/Poly(MMA-co-MSMA)复合材料

以钛酸异丙酯(Ti(OPri)4)、锆酸正丁酯(Zr(OC4H9)4)为无机前驱物原料,γ-甲基丙烯酰氧基丙基三甲氧基硅烷(MSMA)为偶联剂,通过原位溶胶-凝胶法成功制备了透明的纳米TiO2-ZrO2/Poly(MMA-co-MSMA)复合材料。通过红外(FTIR)、紫外(UV)、椭圆偏振光谱仪、扫描电镜(SEM)和热重分析仪(TGA)等手段对纳米复合材料进行了表征。研究发现,复合材料的折射率显著提高,随着TiO2-ZrO2无机氧化物含量的增加,633 nm处折射率从1.491升高到1.579。随着无机组分的增加,紫外吸收增强,复合材料中纳米粒子粒径增大,从20~30nm增加到80~90 nm,但复合材料块体始终保持透明。复合材料的热稳定性有明显提高,800℃最高残炭率随着无机物含量的增加而增大,最高达71%。     

Dielectric and Piezoelectric Properties of (Na0.5Bi0.5)(Ti1–xMnx)O3 (x = 0–0.1) Modified Ceramics

Inorganic Materials - We have studied the crystal structure and dielectric and local piezoelectric properties of (Na0.5Bi0.5)(Ti1–xMnx)O3 (x = 0–0.1) modified sodium bismuth...     

Poly(phenylene sulphide) and poly(ether ether ketone) composites reinforced with single-walled carbon nanotube buckypaper: I – Structure,thermal stability and crystallization behaviour

Single-walled carbon nanotube (SWCNT) buckypaper (BP) reinforced-poly(phenylene sulphide) (PPS) and poly(ether ether ketone) (PEEK) composite laminates were manufactured through hot-press processing. Scanning and transmission electron microscopies were used for morphological characterization and qualitative evaluation of the impregnation degree of the BP. The thermal stability, resin and void content of the composites were evaluated through thermogravimetric analysis; a strong increase in the degradation temperatures of the polymers was found. Raman spectra revealed the existence of strong filler–matrix interactions. The glass transition temperature, crystallization and melting behaviour of the composites were investigated through differential scanning calorimetry and their crystalline structure was analyzed by wide angle X-ray diffraction. This investigation confirms that SWCNT-BPs can be used to fabricate high-loading CNT/thermoplastic composites with improved thermal properties.     

Piezoelectric and dielectric properties of 0.98(Na0.5K0.5)NbO3–0.02Ba(ZrxTi(1−x))O3 ceramics

Lead-free 0.98(Na_0.5K_0.5)NbO₃–0.02Ba(Zr_xTi_(1?x))O₃ (0.98NKN–0.02BZT) ceramics with Zr contents were fabricated by a conventional mixed-oxide method. The results indicate that the Zr/Ti ratio significantly influences the structural, piezoelectric, dielectric, and ferroelectric properties of 0.98NKN–0.02BZT ceramics. For the 0.98NKN–0.02BZT (x = 0) ceramics sintered at 1090 °C, the bulk density increased as the Zr contents decreased and showed a maximum value at x = 0. The Curie temperature of the 0.98NKN–0.02BZT ceramics slightly decreased as the Zr contents increased. The dielectric constant, piezoelectric constant, and electromechanical coupling factor of samples were maximized at x = 0, which might be due to the increase in density. A high d₃₃ = 194 pC/N, k_p = 38% were obtained for the 0.98NKN–0.02BZT ceramics sintered at 1090 °C for 4 h.     

Tailored interface with varied electrical performance in core–shell BaTiO3@C/poly(vinylidene fluoride-chlorotrifluoroethylene) dielectric composite film

Journal of Materials Science: Materials in Electronics - Polymer film capacitor with large power density is potentially embedded in energy suppliers and wearable devices. Currently, the strategy of...     

Is It Possible to Obtain Solvent-Free,Li+-Conducting Solid Electrolytes Based on Pure PVdF? Comment on “Self-Suppression of Lithium Dendrite in All-Solid-State Lithium Metal Batteries with Poly(vinylidene difluoride)-Based Solid Electrolytes”

Is It Possible to Obtain Solvent-Free, Li⁺-Conducting Solid Electrolytes Based on Pure PVdF? Comment on “Self-Suppression of Lithium Dendrite in All-Solid-State Lithium Metal Batteries with Poly(vinylidene difluoride)-Based Solid Electrolytes”     

Effect of Poly (Ethylene Glycol) Molecular Weight and Microparticle Size on Oral Insulin Delivery from P(MAA‐g‐EG) Microparticles

Five years of successful work in our lab have shown that graft copolymer networks of poly(methacrylic acid‐g‐ethylene) [P(MAA‐g‐EG)], are very promising candidates for oral drug delivery. In an acidic environment, these copolymers form interpolymer complexes, protecting the active agent from the harsh environment of the gastrointestinal tract. At high pH, these complexes dissociate, causing the polymer to swell and release the drug. Films of P(MAA‐g‐EG) with a monomer ratio of 1:1 (MAA:EG) were prepared by free radical solution UV‐polymerization, washed in order to remove the unreacted monomer, and crushed to form microparticles with different particle size distribution. Previous studies in our lab have focused on using polymer disks in their swelling studies. The swelling properties of polymer disks vs. crushed particles were investigated via equilibrium swelling experiments in this study. Another goal in this study is to compare different PEG chain length (MW‐400 and MW‐1000) and different particle size (150–212 microns, 90–150 microns and 25–90 microns) in their loading and release behavior. After 6 hours of exposing the polymer with the insulin solution we achieved approximately 90% of insulin loading.     

Spark Discharge Doping—Achieving Unprecedented Control over Aggregate Fraction and Backbone Ordering in Poly(3-hexylthiophene) Solutions

The properties of semiconducting polymers are strongly influenced by their aggregation behavior, that is, their aggregate fraction and backbone planarity. However, tuning these properties, particularly the backbone planarity, is challenging. This work introduces a novel solution treatment to precisely control the aggregation of semiconducting polymers, namely current-induced doping (CID). It utilizes spark discharges between two electrodes immersed in a polymer solution to create strong electrical currents resulting in temporary doping of the polymer. Rapid doping-induced aggregation occurs upon every treatment step for the semiconducting model-polymer poly(3-hexylthiophene). Therefore, the aggregate fraction in solution can be precisely tuned up to a maximum value determined by the solubility of the doped state. A qualitative model for the dependences of the achievable aggregate fraction on the CID treatment strength and various solution parameters is presented. Moreover, the CID treatment can yield an extraordinarily high quality of backbone order and planarization, expressed in UV–vis absorption spectroscopy and differential scanning calorimetry measurements. Depending on the selected parameters, an arbitrarily lower backbone order can be chosen using the CID treatment, allowing for maximum control of aggregation. This method may become an elegant pathway to finely tune aggregation and solid-state morphology for thin-films of semiconducting polymers.