Synthesis,characterization, and tribological properties of two‐dimensional Ti3C2

We report on the preparation of two‐dimensional (2D) Ti₃C₂ and its friction and wear properties. Laminated Ti₃AlC₂ was synthesized by pressureless sintering using Ti, Al, and graphite, followed by HF exfoliation and sonication treatment to form 2D‐layered Ti₃C₂, which exhibited individual layer or stack of several layers. Analysis of microstructure and composition was used to confirm the successful exfoliation of laminated Ti₃AlC₂. The tribological behaviors of the as‐prepared 2D Ti₃C₂ as a lubrication additive in base oil were investigated. Results indicate that 2D‐layered Ti₃C₂ can greatly enhance the friction‐reducing and anti‐friction properties of base oil, especially with 1.0 wt% Ti₃C₂. This novel 2D‐layered Ti₃C₂ would be a good candidate for lubricating materials to meet emerging needs in practical applications.     

三元复合材料PANI/Ag/MWNT的电化学行为和比电容

通过原位聚合的方式在银纳米粒子/多壁碳纳米管(Ag/MWCNT)复合材料的表面成功聚合苯胺单体制备了聚苯胺/银纳米粒子/多壁碳纳米管(PANI/Ag/MWCNT)三元复合材料苯．通过对三元复合材料的结构以及表面形貌进行分析,表明聚苯胺层完全包覆了Ag/MWCNT复合材料,形成了核壳式结构．同时银纳米粒子则以单质晶体的形态存在于多壁碳纳米管与聚苯胺层之间．三元复合材料电极在1 mol/L的KOH溶液中具有极低的阻抗,而与聚苯胺电极相比,这些复合材料电极则表现出更低的电阻、更高的电化学活性和更好的循环稳定性．尤其是当苯胺和Ag:MWCNTs质量比为5:5时,该复合材料电极在0.25 A/g的电流密度下表现出最大的比电容值为160 F/g．     

Hydrogels from phospholipid vesicles

It is shown that phospholipid dispersions with a few percent of diacylphosphocholine PC in water can be swollen to single-phase lyotropic liquid crystalline L_α-phases by the addition of co-solvents like glycerol, 1,3-butyleneglycol BG or 1,2-propyleneglycol PG. The birefringent L_α-phases contain small unilamellar and multilamellar vesicles if the temperature of the samples is above the Krafft-Temperature T_m of the phospholipid. When such transparent birefringent viscous samples are cooled down below T_m the samples are transformed into birefringent gels. Cryo-TEM and FF-TEM measurements show that the bilayers of the vesicles are transformed from the liquid to the crystalline state during the transformation while the vesicle structure remains. The bilayers of the crystalline vesicles form adhesive contacts in the gel. Pulsed-field gradient NMR measurements show that two different kinds of water or co-solvent can be distinguished in the gels. One type of solvent molecules can diffuse like normal solvent in a continuous bulk phase. A second type of water diffuses much more slowly. This type of solvent is obviously trapped in the vesicles. The permeability of the crystalline vesicles for water and solvent molecules is much lower in the crystalline state than in the fluid state.     

Transport of water in polyvinyl alcohol films: Effect of thermal treatment and chemical crosslinking

Data on sorption and transport of water in polyvinyl alcohol films, modified by thermal treatment above T_g, or by chemical crosslinking with glutaraldehyde at different crosslinking degrees, are presented. Equilibrium swelling is constrained by both treatments, except for low degrees of crosslinking where the said reduction is counterbalanced by the partial loss of crystallinity. Analysis of the resulting water uptake kinetics indicates that viscous relaxation effects are, at least partly, responsible for the observed non-Fickian kinetic behavior. Thermodynamic diffusion coefficients of water, D_W, and relaxation frequencies of the swelling polymer, β_W, are determined by application of a theoretical model accounting for relaxation-dependent sorption kinetics in glassy polymers. The results indicate that the effect of both heat-treatment and chemical crosslinking is more intense on the macromolecular relaxation process than on the diffusion coefficient of water. Comparison of the release kinetics of a model drug from as-prepared, non-crosslinked and from crosslinked matrices indicate that the retardation of macromolecular relaxations process induced by crosslinking results in a more uniform release rate.     

Fast synthesis of temperature-sensitive PNIPAAm hydrogels by microwave irradiation

A novel method, microwave irradiation synthesis, is proposed for the preparation of thermo-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels. The PNIPAAm hydrogels were separately synthesized by using microwave irradiation method and water-bath heating method. Chemical groups, lower critical solution temperature (LCST) and surface morphology of these PNIPAAm hydrogels were characterized by FT-IR, DSC and SEM. Swelling ratios of the gels were measured gravimetrically in the temperature range from 10.0 to 60.0 °C. Results showed that (1) the use of microwave irradiation can greatly shorten the reaction time required for PNIPAAm hydrogel synthesis from several hours to several minutes in comparison with water-bath heating method, and obviously improve the yields of the PNIPAAm gels, which were up to 99% after a short reaction time; (2) SEM micrographs and textural measurement revealed that the gels synthesized using microwave irradiation had more porous structure, and their average pore sizes and specific surface areas were larger than those of the gels synthesized using water-bath heating method; and (3) the PNIPAAm hydrogels synthesized using microwave irradiation had much higher swelling ratios at 10.0 °C below the LCST, and had lower swelling ratio at 60.0 °C above the LCST compared to the hydrogels synthesized by water-bath method.     

The selective and enhanced adsorptive behaviors of supramolecular recrystallized 1,3,5-benzenetricarboxylic acid assembled nano-bacterial cellulose

The effluent discharge produced in the textile printing and dyeing, leather and other fields, will cause the irreversible environmental pollution and extremely threatening safety of living organisms. The appropriate and efficient disposal method of dyestuff originated wastewater has been widely concerned in the past decades. In this study, the recrystallization of 1,3,5-benzene tricarboxylic acid (RCTMA) was put forward via a hydrothermal method to form the supramolecular RCTMA-based hexamer and thereafter assembled into the porous nano-bacterial cellulose (NBC) to construct the RCTMA@NBC composite. The morphology and surface properties of RCTMA@NBC were examined by scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy. This RCTMA@NBC was employed to adsorb methylene blue (MB) adjusting the pH, temperature, and dosage of adsorbent. The result showed the maximal absorption capacity of RCTMA@NBC appeared under pH = 7.1 and higher temperature will hinder the adsorption of dyes. Moreover, the adsorption isotherms and kinetics were evaluated which was more confirmed to Langmuir model and quasi-second-order kinetic equation, and the simulated maximum adsorption capacities of MB was 1162.12 mg/g. Moreover, cationic golden XGL and anionic brilliant crocein were selected to further verify the distinct adsorptive behavior. The excellent affinity towards cationic dyes proved the easy combination was based on the chemical force originated from mutual attraction between opposite charges, π–π interactions, and H-bonding, whereas the poor attraction for brilliant crocein was due to the electrostatic repulsion between sulfonic and carboxyl groups. The synthesized RCTMA@NBC possesses higher efficiency and selective adsorption, which exhibits the promising potential in the field of precise treatment of organic dye wastewater.     

不同封装材料的中功率GaN基LED器件老化分析

针对中功率蓝光及相应的白光LED器件进行加速老化实验,并具体分析了器件中硅胶和绿红混合荧光粉等封装材料对老化行为的影响和失效机理。在测试器件的光电老化行为之后,利用反射光谱和飞行时间二次离子质谱对失效器件进行了结构分析。结果表明,温度和湿度对蓝光和白光器件老化行为具有不同的影响。对于中功率蓝光LED而言,其光衰的主要原因是由于S、Cl等元素的引入及氧化等因素引起的黄化导致了透明硅胶反射率的下降。而对于绿红混合荧光粉组成的中功率白光LED来说,其光衰和色漂问题主要归结于在高温特别是高湿环境下工作,器件中荧光粉和硅胶等封装材料发生了一些化学反应,使荧光粉发生分解,并引起了荧光转换效率的下降。     

Co γ-ray irradiation effect and degradation behaviors of a carbon nanotube and poly(ethylene-co-vinyl acetate) nanocomposites

This paper describes the process of manufacturing a new nanocomposite material, which involves adding a carbon nanotube (CNT) to improve EVA's physical characteristics such as weak radiation resistance and thermal properties. We irradiated the prepared samples with doses of 50 kGy, 100 kGy and 200 kGy at a dose rate of 5 kGy/h and examined their thermogravimetric characteristics, activation energy, degradation progress, and CNT dispersion using a thermogravimetric analyzer (TGA), chemiluminescence (CL), and a field emission scanning electron microscope (FESEM). Experimental results indicated that the samples with a CNT had higher DTG 2nd peak temperatures than those without a CNT. Activation energy of the samples reduced as the irradiation dose and the CNT content increased. In the second CL experiment, the CL intensity rapidly declined as the temperature, irradiation dose and the CNT content increased. Finally, examination of the fracture surfaces in the FESEM experiment indicated that the lamella structure of the EVA changed as the irradiation dose increased. We were also able to observe that samples with a CNT were aggregated and dispersed in numerous lumps.     

Ageing properties of polyamide-12 pipes exposed to fuels with and without ethanol

The chemical and physical properties of polyamide-12 (PA12) fuel pipes/lines, aged for ≤2400 h at 110 °C, have been investigated. The pipes, containing fuel with or without ethanol, were either of a single PA12 layer, or of two PA12 layers surrounding a poly(vinylidene fluoride) barrier layer. The molar mass of the inner surface region obtained by size-exclusion chromatography was reduced during ageing, and optical microscopy revealed a surface that was partly dissolved in the presence of ethanol. Infrared spectroscopy revealed a rapid loss of plasticiser, especially in the presence of ethanol, and the fuel contained plasticiser and other polymer related components. Immersion tests at 60 °C showed that the swelling of the pipe and the amount of dissolved material were greatest for the fuels with intermediate ethanol content (50 vol.%). Aged samples experienced an increase in melting point, presumably, to a large extent, due to the loss of plasticiser and/or PA12-related components. In addition, for several samples, the crystallinity seemed to increase with ageing.     

Splitting tendency of cellulosic fibers. Part 3: splitting tendency of viscose and modal fibers

The splitting tendency of viscose and modal fibers in aqueous alkali solutions of LiOH, NaOH, KOH and TMAH was investigated. The viscose fibers splitted up to 5–7 fibrils, whereas modal fibers splitted up to 2–4 fibrils depending on alkali type and concentration. The fibrillar structure of lyocell enables it to split more (15–20 fibrils) than viscose and modal fibers. Splitting occurs where internal stress of fiber is high due to different alkali or void distribution inside fiber. The splitting test couldn’t be achieved for viscose and modal fibers between 1 and 5 M concentration of NaOH and TMAH solutions due to breakage of fibers during test. Above 5 M concentration, no split can be observed due to even distribution of alkali inside fiber. Paper presented at the 7th World Textile Conference, AUTEX 2007, Tampere, Finland, 26–28 June 2007. Christian-Doppler Laboratory of Textile and Fiber Chemistry of Cellulosics is a Member of European Polysaccharide Network of Excellence (EPNOE), www.epnoe.org