Fracture mechanisms in rigid core-shell particle modified high performance epoxies

The fracture mechanisms of a high performance epoxy system modified with two types of preformed rigid core-shell particles (RCSP) were investigated. The use of the preformed RCSP anables the control of the dispersion of the toughener phase in the epoxy, which, in turn, allows the mechanical properties of the modified epoxy to be optimized. The toughening effect via the RCSP modification is found to be as good as that via the core-shell rubber modification. The moduli andT _g of these RCSP-modified epoxies are virtually unaltered via the RCSP modification, when compared with the neat epoxy resin equivalent. The toughening mechanisms in these toughened systems appear to be predominantly crack deflection, crack bifurcation, and microcracking. Approaches for effective toughening of high performance polymers via rigid polymers are discussed.     

单分散二氧化钛超微粒子的制备

以四丁氧基钛为原料，采用溶胶－凝胶法制备了超微二氧化钛粉末．改变热处理气氛、升温速率、水与四丁氧基钛的摩尔比以及溶剂，分别得到７ｎｍ球形单相锐钛矿以及四方形（４０ｎｍ×１０ｎｍ）、球形（４４ｎｍ）的主相金红石超微粒子．     

1H-NMR Relaxation of Water Molecules in the Aqueous Microcrystalline Cellulose Suspension Systems and Their Viscosity

An intensive study for aqueous microcrystalline cellulose (MCC) suspensions was carried out in view of the relationship between a viscosity and a 1H spin-spin relaxation time (T2) of water. An investigation was carried out for four suspension systems with the different particle size distributions. The proton mole ratio () of bound water against MCC particles and T2 of bound water (T2,b) were evaluated from the T2 values obtained by Carr-Purcell- Meiboom-Gill (C.P.M.G) method and those by solid echo method, respectively. As a result of these analyses, the T2,b value for the aqueous MCC suspension was evaluated as 5 × 10–3 s and it was found that the system having a larger tended to show a higher viscosity. By relating the above results to the observation of the suspensions by an optical microscope, it was concluded that a network formed by MCC particles plays an important role in generating a high viscosity of MCC suspension, and that an averaged mobility of water molecules is sensitively affected by the network structure.     

Robust interface on ENR-50/TiO2 nanohybrid material based sol-gel technique: Insights into synthesis,characterization and applications in optical

In this work, the sol–gel technique was used to prepare a new organic–inorganic hybrid from Epoxidized Natural Rubber (ENR-50) and Titanium dioxide (TiO₂) by blending different content of titania precursors (10, 30, and 50 wt%) with an ENR-50 matrix. A wide range of analyses was conducted to understand the nature of this hybrid and also to evaluate its potential uses in applications required high refractive index such as micro optical and optoelectronic devices. Results indicated that the ring-opening reaction of epoxide groups in ENR-50 increased with the increase of titania content in the hybrid resulting a strong bonding between titania and ENR-50 through TiOC bond, which was observed in FTIR spectrum at 1027–1028 cm⁻¹. It is also observed a slight decrease in the intensity of the amorphous peak along with a new crystalline peak appeared at 2θ = 23 and 27° due to the crystalline nature of titania. The hybrids showed three thermal degradation steps in the range of temperature 76 to 769 °C due to the existence of the Ti moieties with the mixture of polymer chains, which in turn shifted the T_g at 24.3, 26.9 and 28.1 °C for the hybrid at 10, 30, and 50 wt% TiO₂ compared to the T_g of ENR-50 at −18.4 °C respectively. The morphology of the ENR-50 showed clear changes during of the synthesis of ENR-50/TiO₂ hybrids, these changes were proven by SEM, TEM, and AFM analyses. Uv–Vis results showed that the higher wavelength peak at 293 nm has shifted to 296, 298 and 300 nm for the hybrid at 10, 30, and 50 wt% TiO₂ respectively due to the strong interaction between titania precursors and ENR-50 matrix. Furthermore, the hybrids showed good optical transparency in the visible light range.     

Dual-Phase structure of polymer electrolytes comprised of NBR/SBR latex films swollen with lithium salt solution

Dual-phase polymer electrolytes (DPE) that have high ionic conductivity (> 10^?3 S/cm) and good mechanical strength were prepared by mixing NBR and SBR latices and casting films. The latex films absorbed large quantities of lithium salt solution (e.g., 1M lithium perchlorate in γ-butyrolactone) to obtain DPE films but did not dissolve with swelling. The NBR phase is polar and was impregnated selectively with the polar lithium salt solution, whereas the SBR phase is nonpolar and formed a mechanically-supportive matrix. Transmission electron microscopic (TEM), electron energy loss spectral (EELS), and energy-dispersive x-ray (EDX) analyses showed microscopically the dual-phase structure. Evidence for swelling by lithium salt solution was found only in the NBR phase and not in the SBR phase by EDX microanalysis. Ionic conductivity as a function of NBR content or swelling degree showed clearly that a percolation threshold for ionic conductivity exists. © 1994 John Wiley & Sons, Inc.     

Laser Doppler anemometry under plasma conditions. Part II. Measurements in an inductively coupled r.f. plasma

Laser Doppler anemometry is used for the measurements of the plasma and particle velocity profiles in the coil region of an inductively coupled r.f. plasma. Results are reported for a 50 mm i.d. induction plasma torch operated at atmospheric pressure with argon as the plasma gas. The oscillator frequency is 3 MHz and the plate power is varied between 4.6 and 10.5 kW. Plasma velocity measurements are obtained using a fine carbon powder as a tracer. Measurements are also given for larger silicon particles ( ) centrally injected into the discharge under different operating conditions.Nomenclature d _p particle diameter - P ₀ plasma power - Q ₁ powder carrier gas flow rate - Q ₂ plasma gas flow rate - Q ₃ sheath gas flow rate - r distance in the radial direction - V axial plasma velocity - V _p axial particle velocity - Z distance in the axial direction - standard deviation     

Cation-crown ether complex formation in water. II. Alkali and alkaline earth cations and 12-crown-4, 15-crown-5, and 18-crown-6

The stability constants and the partial molal volume and isentropic partial molal compressibility changes of complex formation between cations and crown ethers in water at 25°C are presented. The cations involved are Na⁺, K⁺, Rb⁺, Cs⁺, Ca²⁺, and Ba²⁺, and the crown ethers are 12-crown-4, 15-crown-5, and 18-crown-6. Values of V of complex formation have been discussed in terms of two simple models, one based on the scaled particle theory, and the others on the Drude-Nernst continuum model. The results indicate that the charge of the potassium cation in 18-crown-6 is especially well screened from the water. On this basis hydration numbers of complexed cations have been calculated. This shows that the size of the cation compared to the crown ether hole is important for the contacts between complexed cations and water.     

WATER STATES IN SBR BASED WATER SWELLING RUBBER

Water swelling rubber (WSR) was prepared by reaction blending SBR andsodium polyacrylate (PAANa). The existing states of water in the WSR was studied bymeans of DSC and TG. It was found that water exists in three states: nonfreezing water,bound freezable water and free water. The relationships between water states and structureof PAANa were investigated. The results showed that the amount of non-freezing waterwas related to total water content, and the ratio of non-freezing water versus -COONagroups on PAANa (mol/mol) was about 4. However, total water content slightly affectedthe content of bound freezable water and remarkably affected the amount of free waer.     

类球形正交LiMnO2的制备、微结构和电化学性能

以共沉淀法得到的类球形MnCO₃为前驱物，制备了类球形正交LiMnO₂(So-LiMnO₂)，采用XRD、SEM和N₂吸附技术对样品进行表征；与非球形正交LiMnO₂(No-LiMnO₂)进行了对比研究。结果表明：o-LiMnO₂的堆垛层错度、结晶状况、颗粒形貌和大小与前驱物的微结构密切相关；在80次电化学循环测试过程中，So-LiMnO₂经15次循环可达最大的放电容量152 mAh·g^-1，其容量衰减平均每次循环0.58 mAh·g^-1；而No-LiMnO₂要经过38次循环才能达到最大放电容量128 mAh·g^-1，容量衰减平均每次循环高达1.24 mAh·g^-1。TEM和EDS分析证明：由一次粒子团聚的类球形So-LiMnO₂能有效地抑制电解液对材料的腐蚀、减少Mn的溶解，从而提高了电化学循环能力。     

硅氧烷乳液聚合过程中大颗粒形成机理研究：Ⅰ.阳离子型乳液的耐电解质…

探讨了二甲基聚硅氧烷阳离子型乳液耐电解质稳定性的影响因素。结果表明，加入少量的非离子型表面活性剂与阳离子型乳化剂并用进行乳液聚合，可以保护乳液粒子，防止由于电解质引的乳液粒子的相互凝聚而形成大颗粒。