Effects of excluded volume and hydrodynamic interaction on the deformation, orientation and motion of ring polymers in shear flow

A ring polymer is a classical model to explore the behaviors of biomacromolecules. Compared with its linear counterpart in shear flow, the ring polymer should be more sensitive to excluded volume and hydrodynamic interaction attributed to the absence of chain ends. We carried out multiparticle collision dynamics combined with molecular dynamics simulation to study the effects of excluded volume and hydrodynamic interaction on the behaviors of ring polymers in shear flow. The results show that in the absence of the strong excluded volume interaction, the ring polymer prefers a two-strand linear conformation with high deformation and orientation in the flow-gradient plane, and the tank-treading motion is nearly negligible. Ring polymers without excluded volume show no significant difference from linear polymers in the scaling exponents for the deformation, orientation and tumbling motion. We also observed that the hydrodynamic interaction could efficiently slow down the relaxation of ring polymers while the scaling exponents against the Weissenberg number have rarely been affected

Dual-shape memory effect in radiation crosslinked thermoplastic blends: fabrication, optimization and mechanisms

Recently, as an important class of mechanically active smart materials, thermoplastic dual-shape memory polymers (SMPs) have attracted notable attention and can be fabricated in many different manufacturing techniques. Here in this paper, we present experimental results, demonstrating a cost-effective manufacturing technique to enable thermoplastic SMPs with enhanced properties for a wide variety of applications. Thermoplastic SMPs based on low density polyethylene (LDPE) and polypropylene (PP) with various compositions were prepared by melt compounding, followed by a post-processing of e-beam irradiation at 5, 10, 15, 25, 50 and 100 kGy. SEM, DSC, tensile test, rheological properties measurement, sol/gel analysis and shape memory test were performed sequentially to investigate the relationship between the phase morphologies, the content fluctuations, the e-beam irradiation and the shape memory performances. In addition, we also optimized the fabrication process and studied mechanisms of shape memory performances. It was found that the melting point associated to the LDPE soft phase T-m,T-LDPE is almost independent of the content fluctuations. At the same time the mechanical properties (determined at 25 degrees C) and rheological properties (measured at 180 degrees C) can be varied systematically by controlling the structure and radiation dose. More importantly, the results also revealed that (1) irradiated LDPE-rich blends were more suitable and effective than both irradiated PP-rich and nonirradiated blends to be dual-SMPs with advantageous shape memory properties, and (2) increased radiation dose could give rise to enhanced shape recovery capacity without significantly weakening the shape fixity

Achieving grazing-incidence ultra-small-angle X-ray scattering in a laboratory setup

A grazing-incidence sample stage was designed for realizing grazing-incidence scattering measurements, especially in the ultra-small-angle regime, in a modified Xenocs Xeuss system in the laboratory. The designed sample stage, which is composed of four separate motorized positioning stages, allows the sample to be moved along four different directions to locate it in the proper position for scattering measurement. In an effort to realize grazing-incidence ultra-small-angle scattering (GIUSAXS) measurements, both the separation of the collimation slit systems and the sample-to-detector distance have been lengthened. At a separation of the collimation slit systems of 2400mm and a sample-to-detector distance of 6558mm, the effective smallest scattering vector magnitude q(min) reaches 0.01nm(-1). A colloidal crystalline thin film obtained from drying a polystyrene latex dispersion on silicon substrate was measured in the setup in GIUSAXS mode at different beam sizes. The resultant GIUSAXS patterns at smaller beam sizes reveal fine crystalline structures in the film

Luminescence properties of a novel reddish orange long-lasting phosphorescence phosphor Zn2P2O7:Sm3+, Li+

In this article we synthesized a series of new reddish orange long-lasting phosphorescence phosphors by co-doping Li+ ions into Sm3+ activated alpha-Zn2P2O7, characterized their luminescence properties, and evaluated the effect of Li+ co-doping on both photoluminescence and Phosphorescence. The results showed that both the photoluminescence and Phosphorescence originated from characteristic reddish orange emissions of Sm3+ from its 4f-4f transitions of (4)G(5/2)-H-6(5/2), (4)G(5/2)-H-6(7/2) (4)G(5/2)-H-6(9/2) and (4)G(5/2)-H-6(11/2). Besides markedly enhancing the photoluminescence intensity of Sm3+, the Li+ entering into the crystal lattice also promoted the long lasting phosphorescence performance via modifying the defect levels in the phosphors. The optimal long afterglow material was achieved when the Li+ concentration is 2 mol%. This phosphor shows bright reddish orange phosphorescence which could last for more than 3 hours in the dark. Four peaks appeared in its thermoluminescence curve, and the one at around 350 K was proved to be responsible for the occurrence of long lasting phosphorescence. The release of the captured electrons in the defect levels corresponding to this TL peak in room temperature to emission centers of Sm3+ underwent a tunneling process

A Monte Carlo study on LCCC characterization of graft copolymers at the critical condition of side chains

Liquid chromatography at the critical condition (LCCC) has been used to characterize graft copolymers based on the assumption that one of the copolymer blocks becomes chromatographically "invisible" at the critical condition of the corresponding homopolymer. We investigate the validity of this assumption with lattice Monte Carlo simulations of A-g-B graft copolymers modeled as either random walk (RW) or self-avoiding walk (SAW) chains composed of multiple invisible B blocks grafted to an A backbone that is either in size-exclusion chromatography (SEC) or liquid adsorption chromatography (LAC) mode. The simulations show that, in agreement with recent experimental results, the B blocks have a small, but noticeable, impact on the overall elution of the graft copolymer. This influence exists even when the chains are modeled as RWs, indicating that its fundamental origin is due to chain connectivity, not excluded volume interactions. In general, both models show that grafting B blocks to an A backbone in SEC mode tends to increase copolymer retention, while grafting B blocks to an A backbone in LAC mode tends to decrease copolymer retention. When the copolymer is modeled as a SAW, the excluded volume interaction increases the entropic penalty associated with the addition of a B block and, therefore, the addition of B blocks in SAW chains is more likely to result in a decrease in the retention time of the copolymer when the A backbone is in LAC mode. (C) 2015 Elsevier Ltd. All rights reserved

Polyaniline electrospinning composite fibers for orthotopic photothermal treatment of tumors in vivo

A nanocomposite fabricated by electrostatic spinning, which incorporated polyaniline nanoparticles into poly(epsilon-caprolactone) and gelatin (PG), was used to form nanofiber fabrics. Polyaniline nanoparticles have a strong optical absorption at near-infrared (NIR) wavelengths and can convert optical energy into thermal energy under 808 nm laser irradiation, allowing them to ablate tumor cells thermally. Pieces of the nanocomposite were surgically implanted into tumors in mice, and orthotopic photothermal therapy was performed. The experimental results in vivo suggested that polyaniline PG can inhibit tumor growth efficiently by converting optical energy into thermal energy to ablate tumor cells

A study on the effective substance of the Wu-tou formula based on the metabonomic method using UPLC-Q-TOF-HDMS

The Wu-tou formula (WTF) is a Chinese medicine formula which has been applied to treat rheumatic arthritis (RA) and pain of joints for more than a thousand years. In this study, a pharmacodynamics combined urinary metabonomic study using UPLC-Q-TOF-HDMS was performed to assess the holistic efficacy of the Traditional Chinese Medicine (TCM) Wu-tou formula for treating RA in rats. Eighty male Sprague-Dawley rats were randomly divided into eight groups, named as the healthy control group (HG), the model group (AIA), the WTF group and five single herb groups. The treatment groups and the model group were induced for treating rheumatoid arthritis by using complete Freund's adjuvant. Histological results assessed the joint damage and several biochemical parameters such as IL-1 beta, TNF-alpha, SOD and MDA were used to evaluate inflammation injury and oxidative stress. Based on the results, a metabonomic investigation was conducted to study the mechanism of the WTF and single herb treatment groups for treating RA. Multivariate statistical analyses such as PCA and OPLS-DA were used to identify potential biomarkers in urine. As a result, twenty-six potential biomarkers have been found by comparison with the model and the WTF treatment group. The potential biomarkers mainly affect the phenylalanine, tyrosine and tryptophan biosynthesis pathway and the taurine and hypotaurine metabolism pathway. Aconiti Radix Preparata and Ephedrae Herba showed better effects on treating RA from the integrated evaluation by histological results, biochemical parameters and pattern recognition analysis. A comprehensive evaluation of the different therapeutic effects and the mechanism of each herb in the WTF for treating RA was performed in this research

稀土发光材料的研究进展

稀土发光材料已在众多领域获得广泛的应用,并且已成为稀土应用的主要领域之一。本文归纳了白光LED用稀土荧光粉、稀土光转换材料、稀土上转换发光材料、稀土纳米发光材料、真空紫外发光材料、稀土配合物电致发光材料和稀土闪烁体等的研究最新进展,并对未来发展趋势进行了展望

磷酸酯钕催化体系对异戊二烯聚合的影响

以Nd(P204)3(简称Nd)/Al(i-Bu)2H(简称Al)/Al(i-Bu)2Cl(简称Cl)为催化剂,对异戊二烯(Ip)进行聚合,考察了Ip聚合的影响因素,并通过傅里叶变换红外光谱表征了聚合物的微观结构。结果表明,随着Al/Nd(摩尔比)的增大,聚合收率增大,聚合物的数均分子量减小,分子量分布变宽,顺式-1,4-结构摩尔分数下降,但均在98%以上;随着Cl/Nd(摩尔比)的增大,聚合收率先增大后减小,聚合物的重均分子量(珚Mw)减小,分子量分布变宽,顺式-1,4-结构摩尔分数略有下降,但均超过96%;随着三元陈化时间的延长,聚合收率减小,聚合物的珚Mw增大,分子量分布变窄,顺式结构无明显变化;随着聚合温度的升高,聚合收率先增大后减小,聚合物的珚Mw减小,分子量分布变宽,顺式-1,4-结构含量下降;在Al/Nd为5,Cl/Nd为2.5,三元陈化时间为60 min,聚合温度为30℃的最佳反应条件下所得聚合物的顺式-1,4-结构摩尔分数达到98.74%