Polymer adsorption in the grafting reactions of hydroxyl terminal polymers with multi-walled carbon nanotubes

Melt stirring of non-functional polymers such as poly(ethylene oxide) dimethylether (PEO-Me) and polystyrene (PS-H) with multiwalled carbon nanotubes (MWNTs) in the absence of solvent for 48 h induced a substantial amount of polymer adsorption on the MWNTs. The chloroform extraction of the reaction products using centrifugation yielded black colored solutions exhibiting UV absorbance corresponding to the presence of MWNTs. The adsorption of polymer was confirmed on the surfaces of solvent washed residual and recovered MWNTs from the reactions using thermogravimetric analysis (TGA) and FT-IR spectroscopy. Covalent grafting reactions carried out using hydroxyl-terminated PEO-OH and PS-OH with acid chloride containing MWNTs under identical melt stirring condition produced similar results. The presence of polymer on the residual and recovered MWNTs irrespective of the nature of the terminal groups indicates that the adsorption of polymers poses a problem in accurately determining the grafting efficiency. FT IR spectra of the PEO-g-MWNTs shows a substantial shift in CH stretching vibrations indicating a plausible weak intermolecular interaction with π electrons of the MWNTs.     

Examination of the fundamental relation between ionic transport and segmental relaxation in polymer electrolytes

Replacing traditional liquid electrolytes by polymers will significantly improve electrical energy storage technologies. Despite significant advantages for applications in electrochemical devices, the use of solid polymer electrolytes is strongly limited by their poor ionic conductivity. The classical theory predicts that the ionic transport is dictated by the segmental motion of the polymer matrix. As a result, the low mobility of polymer segments is often regarded as the limiting factor for development of polymers with sufficiently high ionic conductivity. Here, we show that the ionic conductivity in many polymers can be strongly decoupled from their segmental dynamics, in terms of both temperature dependence and relative transport rate. Based on this principle, we developed several polymers with “superionic” conductivity. The observed fast ion transport suggests a fundamental difference between the ionic transport mechanisms in polymers and small molecules and provides a new paradigm for design of highly conductive polymer electrolytes.     

Molecular weights of polyethylene and polypropylene by vapor pressure osmometry at elevated temperatures

The Wescan Model 232-A VPO was modified with a 12 volt regulated power supply for supplying bridge current and with thermocouples to allow for direct digital readout of the syringe box and measuring chamber temperatures. The modified instrument was used to measure M _n of standard (NBS) polyethylenes. Agreement with NBS values was good (within 10%) for M _n < 3 × 10⁴ and fair (within 20%) for M _n = 1 × 10⁵. Results on M _n of commercial polypropylenes are also reported.     

Adaptive control of a hybrid electric vehicle

A decentralized adaptive control system (ACS) for a four motor-generator four-wheel drive hybrid electric vehicle (HEV) is designed and its ability to deal with unknown tire dynamics, changing road surfaces, and vehicle loading is evaluated. A system composed of four separate adaptive controllers is designed to control the vehicle's speed, steering, side slip, and energy management system. A nonlinear simulation model for the vehicle dynamics and its power train components is developed and used to evaluate the performance of the ACS, while the vehicle is simultaneously turning and accelerating or braking under varying loading and icing conditions.     

Zr–Al共掺对ZnO光催化剂结构和催化性能的影响

利用水热处理结合焙烧的方法分别制备了Zr、Al掺杂及Zr–Al共掺的ZnO光催化剂。研究了制备的光催化剂样品的相结构和光谱性能;以紫外光（λ=254nm）为光源,酸性橙Ⅱ为降解对象,进行光催化活性测试;考察了Zr、Al掺杂对ZnO光催化剂反应活性的影响。研究表明,制备的产物均为六方晶系纤锌矿结构的ZnO;Zr、Al掺杂及Zr–Al共掺的ZnO样品的光催化活性相对于纯ZnO均有较大程度的提高,而且Zr–Al共掺的ZnO的光催化性能明显优于单一掺杂的。Zr–Al共掺可以明显改善ZnO表面状态,使ZnO具有更丰富的表面羟基,同时可以抑制光生电子–空穴对的复合,从而有利于光催化活性和稳定性的提高。     

爱上不起眼的宝贝

<正>他掌管整个香港食品供应,玩的却是火柴盒、冷门的化石甚至戏院的门票,60余年乐此不疲并自成一家。对香港人而言,李广林这名字并不陌生。每逢罐头加价,或米价下调时,屏幕前就会见到他,为大家关心的食品价格来个解说。他和港人的日常生活关系如此密切——他是港九罐头洋酒伙食行商会副理     

Effect of Solvent Quality on Pure and Mixed Brushes

We investigate, theoretically and experimentally, the effect of solvent quality on pure, one-component, and two-component brushes. Both mean-field and self-consistent field models are developed, and their predictions compared to surface forces experiments on polystyrene and mixed polystyrene–polybutadiene brushes. We find that in pure brushes the structure and interactions between surfaces are highly sensitive to solvent quality. In a good solvent, the brush is extended and the interactions are repulsive, while in a poor solvent the brush is “collapsed” and the interactions are strongly attractive. Mixing two incompatible chains significantly reduces the sensitivity of the brush to solvent properties. While one of the chains collapses in a selective solvent, the other chain remains solvated, thus providing long-range repulsive interactions between surfaces. Our experiments show that the interactions between surfaces carrying a 1:1 mixed brush of styrene–butadiene are repulsive even in hexane, a poor solvent for polystyrene. Theoretically, we calculate that incorporating only 10% of an equi-molecular-weight chain into a collapsed brush can eliminate attractive interactions between surfaces.     

Quantitative Characterization of the Fracture Surface of Si Single Crystals by Confocal Microscopy

Experiments are conducted to study the dislocation nucleation conditions at the crack tip in {110}〈110〉 oriented Si single crystals. Specimens with surface cracks are first statically loaded at elevated temperatures for a prolonged period of time to initiate and move dislocations away from the crack tip, then cooled down to room temperature and loaded to fracture to measure the fracture toughness. Fractographic analysis of the fracture surfaces is performed. Distinct wavy patterns on the fracture surface at the initial cleavage crack front are observed, which is attributed to the existence of local mixed mode I/mode III stresses resulting from the inhomogeneous dislocation activity. Confocal microscopy is employed to quantify the fracture surface roughness. The results show that the increase of fracture toughness is directly associated with the increased area of the rough surface, which is characterized by the roughness number or the fractal dimension increment. Our results also demonstrate that dislocation nucleation can occur only at discrete sites. The spacing between these dislocation nucleation sources is of the order of 1 μm. A simple model is developed for the relationship between the fracture toughness and the surface roughness parameters, which is in good agreement with the experimental results.