Quan-Ping Zhang

The coupling relation between chain architectures and secondary flow field determined by an unusual dependence of shish-kebabs on molecular weight of high-density polyethylene

Selecting high molecular weight has become a quite popular approach for effective tuning of more shish-kebabs in semi-crystalline polymers. However, here, an unusual dependence of shish-kebabs on molecular weight of high-density polyethylene (HDPE) is found under the injection molding with a secondary flow. Characterization with electron microscope and X-ray scattering of the crystal structures reveals that the richest shish-kebabs develop in the HDPE with medium high molecular weight (HMW) chains rather than in the HDPE with more HMW chains. Both macroscopic scales (fluid behaviors related to the intensity of flow) and molecular scales (rheological properties related to orientation and relaxation) need to be overall considered and a physical model has been proposed to explain how the coupling between the chain architectures and the secondary flow field contributes to the unusual phenomenon. The factors, such as molecular parameters, interfaces between dispersed phase, and matrix as well as the properties of filler, profoundly influence both the two scales, which can be employed to tune the morphology related to physical properties. These significant results provide a simple but effective morphology control technique under a secondary flow field.

One-dimensional lead borate nanowhiskers for the joint shielding of neutron and gamma radiation: controlled synthesis, microstructure, and performance evaluation

Lead borate nanowhiskers have been successfully prepared by a facile solvothermal method. The morphologies and crystal sizes of the lead borate nanowhiskers are controlled by adjusting the amount of added ammonia hydroxide in the solvothermal reaction. The morphology evolution and structure changes are tracked during the growth process by field SEM, TEM, and XRD, respectively. The as-prepared lead borate nanowhiskers are 60–90 μm in length and 150–500 nm in diameter and possess typical single-crystal attributes. The influence of lead borate nanowhiskers on the mechanical properties, thermal conductivity, and radiation shielding performance of polymer composites is also discussed. The results show that lead borate nanowhiskers can significantly improve these properties of the composites. The excellent integrated properties contribute to the application of the materials for shielding mixed neutron and gamma radiation.

Hierarchical crystalline morphologies induced by a distinctly different melt penetrating process

Recently, a melt penetrating process which allows one kind of polymer melt to penetrate another polymer melt has been achieved on our home-made multi-melt multi-injection molding (MMMIM) instrument. It is the first time that hierarchically crystalline morphologies induced by melt penetration of the melt with different interactions are reported. In this work, high density polyethylene (HDPE) melt was penetrated by a distinctly different polypropylene (PP) melt and also by the same HDPE melt for comparison. The crystalline morphologies were observed using SEM and PLM, and the lamellar structures were characterized using a synchrotron 2D-SAXS/WAXD. The results showed that β-form transcrystallization occurred along the interface of the PP penetrating sample, and only α-iPP spherulites were observed in the core layer. Interestingly, shish–kebabs with flat lamellae were found in the subskin layer of the PP penetrating sample, while spherulites and cylindrites consisting of a banded-structure were observed in the sample at the penetration of the HDPE melt.

Tailoring chain length and cross-link density in dielectric elastomer toward enhanced actuation strain

Adding ceramic or conductive fillers into polymers for increasing permittivity is a direct and effective approach to enhance the actuation strain of dielectric elastomer actuators (DEAs). Unfortunately, the major dielectric loss caused by weak interfaces potentially harms the electro-mechanical stability and lifetime of DEAs. Here, we construct a desired macromolecular network with a long chain length and low cross-link density to reduce the elastic modulus of silicone elastomers. Selecting a high molecular weight of polymethylvinylsiloxane and a low dose of the cross-linker leads the soft but tough networks with rich entanglements, poor cross-links, and a low amount of defects. Then, a ductile material with low elastic modulus but high elongation at break is obtained. It accounts for much more excellent actuation strain of Hl in comparison to that of the other silicone elastomers. Importantly, without other fillers, the ultralow dielectric loss, conductivity, and firm networks possibly promote the electr...

Graphene oxide promoted synthesis of p -phenylenediamine antioxidants

Three p-phenylenediamine antioxidants (p-phenylenediamine-N,N,N′,N′-tetrapropionic acid tetramethyl ester, p-phenylenediamine-N,N,N′-tripropionic acid trimethyl ester, and p-phenylenediamine-N, N′-dipropionic acid dimethyl ester) were successfully synthesized via atom-economic aza-Michael addition of pphenylenediamine to methyl acrylate p-romoted by graphene oxide in water. The synthesized compounds were characterized by NMR, ESI-MS spectra, and elemental analyses. The effects of the solvent and graphene oxide on the reaction were investigated.

Numerical simulation and experimental study of PbWO4/EPDM and Bi2WO6/EPDM for the shielding of γ-rays*

The MCNP5 code was employed to simulate the γ-ray shielding capacity of tungstate composites. The experimental results were applied to verify the applicability of the Monte Carlo program. PbWO4 and Bi2WO6 were prepared and added into ethylene propylene diene monomer (EPDM) to obtain the composites, which were tested in the γ-ray shielding. Both the theoretical simulation and experiments were carefully chosen and well designed. The results of the two methods were found to be highly consistent. In addition, the conditions during the numerical simulation were optimized and double-layer γ-ray shielding systems were studied. It was found that the γ-ray shielding performance can be influenced not only by the material thickness ratio but also by the arrangement of the composites.The MCNP5 code was employed to simulate the {\gamma}ray shielding capacity of tungstate composites. The experimental results were applied to verify the applicability of the Monte Carlo program. PbWO4 and Bi2WO6 were prepared and added into ethylene propylene diene monomer (EPDM) to obtain the composites, which were tested in the {\gamma}ray shielding. Both the theoretical simulation and experiments were carefully chosen and well designed. The results of the two methods were found to be highly consistent. In addition, the conditions during the numerical simulation were optimized and double-layer {\gamma}ray shielding systems were studied. It was found that the {\gamma}-ray shielding performance can be influenced not only by the material thickness ratio but also by the arrangement of the composites.

PbWO4 nanofibers for shielding gamma radiation: crystal growth, morphology and performance evaluation

Assembling anisotropic structures with versatility such as good thermal conductivity and mechanical loading for radiation shielding has recently attracted widespread attention. Herein, a facile strategy with (3-mercaptopropyl)trimethoxysilane (KH590) as a surfactant is used to synthesize one-dimensional (1D) PbWO4 structures. Their morphology evolution and crystal phase transition are traced during the growth process by SEM, TEM, and XRD techniques, respectively. The results show that monoclinic PbWO4 nanofibers with typical single-crystal attributes and high production are obtained with the addition of 5 wt% KH590. In addition, although PbWO4 nanoparticles display a slightly high attenuation coefficient for gamma radiation, 1D PbWO4 structures exhibit better thermal conductivity, tensile strength and elongation at break. These findings indicate that the prepared 1D PbWO4 structures have a very promising prospect in the application of state-of-the-art shielding materials for gamma radiation.

Improved hydrogen adsorption of 5A molecular sieves by enhancing its thermal conductivity

Understanding the hydrogen adsorption of porous materials is crucial to the design of high-efficiency hydrogen isotope separation materials. Much importance has been attached to tailoring the structures of materials, while the thermal management during the adsorption is often ignored. Here, we have experimentally found that the hydrogen adsorption capacity of a 5A molecular sieve (5A) is improved by enhancing its thermal conductivity. It can be facilely achieved by constructing rich and firm thermally conductive networks by filling graphite. 5A with 30 wt. % graphite shows a high thermal conductivity of 0.97 W m−1 K−1 and a fast thermal response. Notably, it also displays an enhancement of 15.6 ml/g normalized hydrogen adsorption capacity compared to the neat 5A. This indicates that there is a close relationship between thermal conductivity and hydrogen adsorption. The above demonstrations show that thermal management plays a significant role in hydrogen adsorption and should be seriously considered for designing the materials of hydrogen isotope separation.Understanding the hydrogen adsorption of porous materials is crucial to the design of high-efficiency hydrogen isotope separation materials. Much importance has been attached to tailoring the structures of materials, while the thermal management during the adsorption is often ignored. Here, we have experimentally found that the hydrogen adsorption capacity of a 5A molecular sieve (5A) is improved by enhancing its thermal conductivity. It can be facilely achieved by constructing rich and firm thermally conductive networks by filling graphite. 5A with 30 wt. % graphite shows a high thermal conductivity of 0.97 W m−1 K−1 and a fast thermal response. Notably, it also displays an enhancement of 15.6 ml/g normalized hydrogen adsorption capacity compared to the neat 5A. This indicates that there is a close relationship between thermal conductivity and hydrogen adsorption. The above demonstrations show that thermal management plays a significant role in hydrogen adsorption and should be seriously considered for d...