Promoted formation of stereocomplex in enantiomeric poly(lactic acid)s induced by cellulose nanofibers

Stereocomplex (SC) crystallization between enantiomeric poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) is believed to yield poly(lactic acid) (PLA) with superior physiochemical properties. However, homocrystallization (HC) crystallites are inevitably generated in the PLLA/PDLA blends. Herein, we report a simple approach to fabricate PLLA/PDLA racemic blends with high contents of SC crystallites by introducing cellulose nanofibers (CNFs). The isothermal crystallization results revealed that the half-crystallization time of the PLLA/ PDLA blend was significantly decreased by adding CNFs. Additionally, with the incorporation of 3 wt% modified CNFs, the PLLA/PDLA blend was overwhelmingly crystallized into SC crystallites with no HC crystallite formation. Based on Fourier transform infrared spectroscopy findings, it was speculated that the preferred SC crystallization of PLLA/PDLA/CNF was caused by enhanced interchain molecular interactions between CNFs and PLA. This work presents a feasible and efficient method to fabricate PLA with exclusively SC crystallites, which possesses great potential for producing high-performance PLA materials

Theoretical insights into the substitution effect of phenanthroline derivative ligands on the extraction of Mo (VI)

With the rapid development of nuclear medical imaging, the production of Mo-99 has attracted much attention, because the important medical isotope Tc-99m can be obtained from Mo-99. N,N'-diethyl-N,N'-ditolyl-2,9-diamidel,10-phenanthroline (Et-Tol-DAPhen) has been proven to be an excellent ligand for the extraction of U (VI), while there are still few reports on the extraction of Mo(VI) using this ligand. To investigate the coordination structures of MoO22+ with Et-Tol-DAPhen, we carried out theoretical calculations using scalar relativistic density functional theory (DFT). The analyses of Wiberg indices (WBIs), quantum theory of atoms in molecules (QTAIM) and natural orbitals of chemical valence (NOCV) indicate that the MoO22+ have stronger complexation ability with O atoms compared to N atoms. The bonds between MoO22+ ions and ligands are mainly ionic interactions. The analyses of EDA and the most negative binding energy indicates that complex [MoO2L(NO3)](+) is energetically favorable and Et-Tol-DAPhen has also good extraction ability for MoO22+. Moreover, although both the electron-donating and electron-withdrawing groups have slightly effect on the electronic structures of the [MoO2L(NO3)](+) complexes, Et-Tol-DAPhen modified by the electron-donating group can enhance the extraction ability of MoO22+. This study is helpful to understand the complexation behavior of Et-Tol-DAPhen with MoO22+ and provides useful structural and thermodynamic information for the MoO22+ extraction with phenanthroline derivative ligands

Correlation between dynamic magnetization process and dynamic domains of high saturation induction FeSiBNbCuMo nanocrystalline alloy with dual anisotropies

Improving the high-frequency properties of the relatively high saturation induction alloys is significance for widening the frequency range of the noise suppression of common mode chokes. Herein, transverse magnetic field annealing after having been nano-crystallized (TA) was performed to the as-quenched Fe76Si13B8Nb1.5Cu1Mo0.5 alloy, and the dynamic properties, microstructure, and dynamic domains were in detail studied comparing with those annealed without magnetic field (NA). It was found that TA at 400 degrees C caused an increase in permeability at 50 kHz by 41% and a decrease in core loss at 0.2 T and 50 kHz by 30%, in comparison with those of NA. TA at 400 degrees C induced the ratio of field induced anisotropy constant K-u to average random anisotropy constant to be similar to 1.3 and inhomogeneous rotation, leading to the promoted domain refinement with increasing frequency and improved high-frequency properties, compared with that of NA bears only similar to 5.4 J/m(3). Moreover, the role of dual anisotropies on the magnetic domain structures, dynamic magnetization process and magnetic performances were obtained and its correlation model based on the experimental results was established. These results could provide a good guide for performance optimization to meet higher frequency requirements of common mode chokes application. (C) 2021 Elsevier B.V. All rights reserved

Experimental and numerical study on Mode I and Mode II interfacial fracture toughness of co-cured steel-CFRP hybrid composites

Interfacial fracture toughness of co-cured steel-carbon fiber reinforced plastic (CFRP) hybrid composites were investigated in this paper. To illustrate the effect of the interlayer on the fracture toughness, steel-CFRP hybrid composites were prepared by different manufacturing processes based on steel surface treatment (abrasion or grit blasting) and adhesive-bonding process. The experimental results of double cantilever beam (DCB) tests and end notched flexure (ENF) tests demonstrate that, the Mode I and Mode II interfacial fracture toughness of the hybrid composites can be improved by using a grit blasting surface treatment on steel and introducing an adhesive layer at the steel/CFRP interface. The hybrid composites mainly show fiber/epoxy interfacial failure of CFRP under Mode I loading conditions, while it mostly exhibits adhesive failure of steel/CFRP interface under Mode II loading condition. Moreover, the interfacial tensile strengths of steel-CFRP hybrid composites are predicted by finite element analysis, and both experimental and numerical results confirm the improvement of interfacial fracture toughness

Black phosphorene-cellulose nanofiber hybrid paper as flexible heat spreader

In this work, black phosphorene (BP) was exfoliated by solvent exfoliation of black phosphorus powders in N-methyl pyrrolidone. The BP-cellulose nanofiber (CNF) paper was prepared from the solution containing BP and CNF by vacuum filtrating. The as-prepared BP-CNF paper has a 'brick-and-mortar' structure. The BP-CNF paper has a high in-plane thermal conductivity of 22.3 W m(-1) K-1 at room temperature, benefiting from the thermal transition pathways constructed by the 'brick-and-mortar' structure. In addition, the BP-CNF possesses an excellent flexibility. Our results in this work demonstrate that BP has a great potential in the application of thermal management material

Electrostatic enhanced surface segregation approach to self-cleaning and antifouling membranes for efficient molecular separation

Membranes with excellent antifouling properties and persistent high permeance are eternal pursuits in membrane technology. Herein, we proposed an electrostatic enhanced surface segregation approach toward the antifouling and self-cleaning membranes for molecular separation. A copolymer containing quaternary ammonium (QA) segments was designed as the surface segregation agent in the casting solution, while polysulphonic acid (PSA) was designed as the crosslinking agent in the coagulation bath. Driven by the electrostatic interactions between the positively charged QA and negatively charged sulphonic groups, the copolymer and PSA were in-situ assembled during the non-solvent induced phase separation (NIPS) processes, generating a selective separation layer on the polymeric matrix. The segregation of copolymer was enhanced, leading to a high surface coverage of ionic QA and sulphonic groups and a significantly improved surface hydrophilicity. Accordingly, the membrane exhibited a high water permeance up to 124 Lm(-2) h(-1) bar(-1) with dye rejection over 95%. Moreover, the membrane exhibited excellent antifouling performance with the ultralow total permeance decline of 1.2% and the ultrahigh permeance recovery ratio of 99.8% against emulsified oil, as well as the self-cleaning property against crude oil. Hopefully, this study can afford a novel and generic approach to antifouling and self-cleaning membranes for diverse separations

Atomic Structures and Mechanical Properties of Magnetron Co-Sputtered Zr-V-N Coatings

Zr-V-N coatings with varying Zr and V content were deposited by magnetron sputtering. Transmission electron microscopy (TEM) cross-section images of the coatings show a dense structure with tightly packed V-shaped columns. x-ray diffraction (XRD) and x-ray absorption fine spectroscopy (XAFS) were carried out to characterize the microstructure of the Zr-N-V thin films. The structural models derived from XAFS reveals segregation of metal domains within the Zr-V-N films. The Zr-V-N sample with Zr/V molar ratios around 3.5:1, which has a higher hardness and more stable wear resistance compared with other Zr-V-N coatings, is a promising material for industrial applications

Effects of bulky 2,2 '-substituents in dianhydrides on the microstructures and gas transport properties of thermally rearranged polybenzoxazoles

The chain interactions of hydroxyl polyimide (HPI) precursors, such as chain packing and 7C-7C stacking interactions, significantly affect the microstructures and gas separation performance of the resulting thermally rearranged polybenzoxazoles (TR-PBOs). In this study, HPIs with various 2,2'-substituents in their anhydrides (BPDA-AP, PBPDA-AP, and 12FPBPDA-AP) were prepared through polycondensation of three dianhydrides (4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,2'-diphenyl-4,4',5,5'-biphenyltetracarboxylic dianhydride (PBPDA), and 2,2'-bis(3 '',5 ''-ditrifluommethylphenyl)-4,4',5,5'-biphenyltetracarboxylic dianhydride (12FPBPDA)) with 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (AP). The dihedral angles and rotational barriers for PBPDA and 12FPBPDA were considerably larger than those for BPDA. Thus, the inter- and intra-molecular chain interactions were more pronounced for BPDA-AP than for PBPDA-AP and 12FPBPDA-AP. Consequently, the glass transition and TR temperatures of the HPIs were in the order of BPDA-AP > PBPDA-AP > 12FPBPDA-AP, whereas fractional free volume (FFV) and interchain distances followed the opposite trend. After TR, the FFV and interchain distances of the TR-PBO from BPDA-AP increased more than those from PBPDA-AP and 12FPBPDA-AP, whereas the pi-pi stacking interactions in BPDA-AP were well maintained. Consequently, BPDA-AP-450 exhibited the highest increase in gas permeability relative to its HPI precursor but the poorest plasticization resistance among fully converted TR-PBOs. This work demonstrated that chain packing played a crucial role in the TR behavior, microstructures, and gas transport properties of TR-PBOs

Comparison of the in vitro corrosion behavior of biodegradable pure Zn in SBF, 0.9% NaCl, and DMEM

Zn-based alloys are considered to be the new biodegradable implant materials due to their suitable degradation rate and good biocompatibility. The biocorrosion behavior of pure Zn in 0.9% NaCl, simulated body fluid, and Dulbecco's modified Eagle's medium (DMEM) was investigated by electrochemical and immersion tests. These tests revealed that pure Zn has the lowest corrosion rate in DMEM and the highest in 0.9% NaCl. Aggressive Cl- has an important effect on the corrosion process. Buffering agents, amino acids, and glucose have a close connection with corrosion resistance. Among the three solutions, DMEM with a similar ion concentration and necessary nutriments is recommended as the more suitable choice for estimating biodegradable alloys' in vitro degradation

Laser-induced dynamic alignment and nonlinear-like optical transmission in liquid suspensions of 2D atomically thin nanomaterials

Nonlinear optical property of atomically thin materials suspended in liquid has attracted a lot of attention recently due to the rapid development of liquid exfoliation methods. Here we report laser-induced dynamic orientational alignment and nonlinear-like optical response of the suspensions as a result of their intrinsic anisotropic properties and thermal convection of solvents. Graphene and graphene oxide suspensions are used as examples, and the transition to ordered states from initial optically isotropic suspensions is revealed by birefringence imaging. Computational fluid dynamics is performed to simulate the velocity evolution of convection flow and understand alignment-induced birefringence patterns. The optical transmission of these suspensions exhibits nonlinear-like saturable or reverse saturable absorptions in Z-scan measurements with both nanosecond and continuous-wave lasers. Our findings not only demonstrate a non-contact controlling of macroscopic orientation and collective optical properties of nanomaterial suspensions by laser but also pave the way for further explorations of optical properties and novel device applications of low-dimensional nanomaterials. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen