A theory of plasticity for carbon nanotube reinforced composites

Carbon nanotubes (CNTs) possess exceptional mechanical properties, and when introduced into a metal matrix, it could significantly improve the elastic stiffness and plastic strength of the nanocomposite. But current processing techniques often lead to an agglomerated state for the CNTs, and the pristine CNT surface may not be able to fully transfer the load at the interface. These two conditions could have a significant impact on its strengthening capability. In this article we develop a two-scale micromechanical model to analyze the effect of CNT agglomeration and interface condition on the plastic strength of CNT/metal composites. The large scale involves the CNT-free matrix and the clustered CNT/matrix inclusions, and the small scale addresses the property of these clustered inclusions, each containing the randomly oriented, transversely isotropic CNTs and the matrix. In this development the concept of secant moduli and a field fluctuation technique have been adopted. The outcome is an explicit set of formulae that allows one to calculate the overall stress-strain relations of the CNT nanocomposite. It is shown that CNTs are indeed a very effective strengthening agent, but CNT agglomeration and imperfect interface condition can seriously reduce the effective stiffness and elastoplastic strength. The developed theory has also been applied to examine the size (diameter) effect of CNTs on the elastic and elastoplastic response of the composites, and it was found that, with a perfect interface contact, decreasing the CNT radius would enhance the overall stiffness and plastic strength, but with an imperfect interface the size effect is reversed. A comparison of the theory with some experiments on the CNT/Cu nanocomposite serves to verify the applicability of the theory, and it also points to the urgent need of eliminating all CNT agglomeration and improving the interface condition if the full potential of CNT reinforcement is to be realized.     

Crystallization of propylene–ethylene random copolymers

Of the three melting peaks typical of a propylene–ethylene random copolymer (with 5.1 wt % ethylene) crystallized between 110 and 140 °C, the two higher peaks result from primary and secondary isothermal crystallization, whereas the material crystallized on cooling gives the lowest peak. In contrast to polypropylene homopolymers, which show strong morphological changes developing from the center of a spherulite, copolymer specimens are uniformly crosshatched. The highest melting peak is related to an open crosshatched framework of primary lamellae, and the next lower peak is related to later forming subsidiary lamellae filling the intervening space. The origin and nature of these double peaks are discussed in terms of the fractional crystallization and the ensuing constraints placed on isothermal lamellar thickening as a result of the exclusion of the comonomer from the polypropylene lattice. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3318–3332, 2004     

Luminescent Property of a Supramolecular Silver(I)‐Thiolate Complex Based on Secondary Ag‐S Interactions and Hydrogen Bonds

The supramolecular silver(I)‐thiolate complex [Ag(μ₂‐SC₄N₂H₄)₂(SCN)]_n has been prepared from the reaction of AgSCN and pyrimidine‐2‐thiol in DMF. X‐ray diffraction analysis shows that the supramolecular structure exhibits one‐dimensional chain through the secondary Ag‐S interactions and the chains are further linked by strong hydrogen bonds to form a three dimensional network. The luminescence effect from the silver‐centered state of S→Ag LMCT in solid state is different from that in solution due to the secondary Ag‐S interactions.     

Di­methyl 2‐(4‐bromo­phenyl)‐10,11‐di­methoxy‐2,3,7,8‐tetra­hydro­spiro­[azepino[2,1‐a]­iso­quinoline‐3,9′‐fluorene]‐4,5‐di­carboxyl­ate

The title compound, C₃₈H₃₂BrNO₆, is a new photochromic tetra­hydro­azepinoiso­quinoline (THAI). The longest spiro bond [1.589 (4) Å] can be broken very easily by UV light, leading to ring opening. This explains the photochromic behaviour.     

Developing a novel alkaline anion exchange membrane derived from poly(ether‐imide) for improved ionic conductivity

We have developed a novel alkaline anion exchange membrane derived from poly(ether‐imide) for improved ionic conductivity. The effects of several important parameters on the chloromethylation of the membrane were investigated. These parameters included reaction temperature, reaction time, concentration of chloromethylation agent, concentration of polymer, and the amount of catalyst. The quaternization of the synthesized chloromethylated polymer was studied as well. The results show that all the studied parameters exhibited significant impacts on chloromethylation. Among them, the concentration of the chloromethylation agent played a key role in increasing the chloromethyl functional group attachment onto the polymer. It was found that the gelation could be avoided if these reaction parameters were controlled. It was also found that using an appropriate quaternization approach could significantly improve the ionic conductivity and optimize the conductivity of the membrane even though the functional chloromethyl groups attached to the polymer are limited. Copyright © 2009 John Wiley & Sons, Ltd.