Tuning of shear thickening behavior and elastic strength of polyvinylidene fluoride via doping of ZnO-graphene

ZnO rice like nonarchitects are grafted on the graphene carbon core via a rapid microwave synthesis route. The prepared grafted systems are characterized via XRD, SEM, RAMAN, and XPS to examined the structural and morphological parameters. Zinc oxide grafted graphene sheets (ZnO-G) are further doped in β-phase of polyvinylidene fluoride (PVDF) to prepare the polymer nanocomposites (PNCs) via mixed solvent approach (THF/DMF). β-phase confirmation of PVDF PNCs is done by FTIR studies. It is observed that ZnO-G filler enhances the β-phase content in the PNCs. Non-doped PVDF and PNCs are further studied for rheological behavior under the shear rate of 1–100 s⁻¹. Doping of ZnO-G dopant to the PVDF matrix changes its discontinuous shear thickening (DST) behavior to continues shear thickening behavior (CST). Hydrocluster formation and their interaction with the dopant could be the reason for this striking DST to CST behavioral change. Strain amplitude sweep (10⁻³% -10%) oscillatory test reveals that the PNCs shows extended linear viscoelastic region with high elastic modulus and lower viscous modulus. Effective shear thickening behavior and strong elastic strength of these PNCs present their candidature for various fields including mechanical and soft body armor applications.     

Maskless Preparation of Spatially-Resolved Plasmonic Nanoparticles on Polydimethylsiloxane via In Situ Fluoride-Assisted Synthesis

Here, a fluoride-assisted route for the controlled in-situ synthesis of metal nanoparticles (NPs) (i.e., AgNPs, AuNPs) on polydimethylsiloxane (PDMS) is reported. The size and coverage of the NPs on the PDMS surface are modulated with time and over space during the synthetic process, leveraging the improved yield (10×) and faster kinetics (100×) of NP formation in the presence of F⁻ ions, compared to fluoride-free approaches. This enables the maskless preparation of both linear and step gradients and patterns of NPs in 1D and 2D on the PDMS surface. As an application in flexible plasmonics/photonics, continuous and step-wise spatial modulations of the plasmonic features of PDMS slabs with 1D and 2D AgNP gradients on the surface are demonstrated. An excellent spatially resolved tuning of key optical parameters, namely, optical density from zero to 5 and extinction ratio up to 100 dB, is achieved with AgNP gradients prepared in AgF solution for 12 minutes; the performance are comparable to those of commercial dielectric/interference filters. When used as a rejection filter in optical fluorescence microscopy, the AgNP-PDMS slabs are able to reject the excitation laser at 405 nm and retain the green fluorescence of microbeads (100 µm) used as test cases.     

Enhanced strains of Nb-doped BNKT-4ST piezoelectric ceramics via phase boundary and domain design

A strategy that constructs the morphotropic phase boundary and manipulates the domain structure has been used to design the component of 0.96[Bi_0.5(Na_0.84K_0.16)_0.5Ti_(1-x)Nb_xO₃]-0.04SrTiO₃ (BNKT-4ST-100xNb) to enhance the strain properties for actuator application. Non-equivalent Nb⁵⁺ donor doping modulates the phase transition from the mixture of rhombohedral and tetragonal phases to the pseudocubic phase and results in the coexistence of multiple phases. Moreover, the high-resolution TEM confirms the existence of polar nano regions that contribute to the macroscopic relaxor behaviour. The size of the domains is reduced with increasing Nb⁵⁺, resulting in an enhanced relaxor behaviour. The ferroelectric-relaxor transition temperature decreases from 85 to below 30 °C, implying a non-ergodic to ergodic relaxor transition. An improved strain of 0.56% and a giant normalized strain of 1120 pm/V were achieved for BNKT-4ST-1.5Nb, which were attributed to the unique domain structure in which nanodomains are embedded in an undistorted cubic matrix. Ferroelectric, antiferroelectric, and relaxor phases coexist. As the electric field is large enough, a reversible phase transition occurs. Furthermore, good temperature stability was obtained due to the stability of the nanodomains, and no degradation in strains was observed even after 10⁴ cycles, which may originate from the reversible phase transition and dynamic domain wall. The results show that this design strategy offers a reference way to improve the strain behaviour and that BNKT-4ST-100xNb ceramics could be a potential material for high-displacement actuator applications.     

低分子量聚丙烯酸钾的合成及其应用

采用水溶液聚合法制备了低分子量聚丙烯酸钾（PAAK），并作为新型消焰剂加入单基发射药中。通过火焰原子吸收光谱法测试了PAAK中钾的含量；用乌氏黏度计测定了特性黏度；采用DSC法研究不同pH值的PAAK与硝化棉（NC）的相容性；利用充氮氧弹法对添加PAAK、硝酸钾KNO₃、硫酸钾K₂SO₄的单基发射药的燃烧残渣进行了对比研究。结果表明，合成的PAAK中，钾的质量分数为15.21%，相对分子量在3 000左右，有利于和NC均匀混合，且在中性或微碱性（pH＝7.0~7.5）的情况与NC相容性良好。与传统的KNO₃、K₂SO₄消焰剂相比，PAAK能够和NC均匀混合，制备均质透明的单基发射药；PAAK发射药的燃烧残渣最少，占发射药质量的0.18%。     

Experimental study of crystal anisotropy based on ultra-precision cylindrical turning of single-crystal calcium fluoride

To realize ultimately efficient signal processing, it is necessary to replace electrical signal processing circuits with optical ones. The optical micro-resonator, which localizes light at a certain spot, is an essential component in optical signal processing. Single-crystal calcium fluoride (CaF₂) is the most suitable material for a highly efficient optical micro-resonator. The CaF₂ resonator can only be manufactured by ultra-precision machining processes, because its crystal anisotropy does not allow the application of chemical etching. However, the optical micro-resonator's performance depends definitely on the surface integrity.This study investigated the relationship between surface quality after ultra-precision machining and crystal anisotropy. Firstly, crack initiation was investigated on the (1 0 0), (1 1 0), and (1 1 1) planes using the micro-Vickers hardness test. Secondly, brittle-ductile transition was investigated by orthogonal cutting tests. Finally, cutting performance of cylindrical turning was evaluated, which could be a suitable method for manufacturing the CaF₂ resonator. The most difficult point in cylindrical turning of CaF₂ is that the crystalline plane and cutting direction vary continuously. In order to manufacture the CaF₂ optical micro-resonator more efficiently, analysis was conducted on crack initiation and surface quality of all crystallographic orientations from the perspective of slip system and cleavage.     

硫磷混合酸溶样重铬酸钾容量法测定全铁

介绍了硫磷混合酸溶样重铬酸钾容量法测定矿石中铁含量的方法和步骤。重点讨论了一线生产中的质量控制。     

Effects of corrosion in liquid fluoride salt on the tensile strength of domestic SiC fibers

The relationship between the tensile strength of corroded domestic second-generation (2ed-gen) SiC fibers at various temperatures for 500 h in 46.5LiF-11.5NaF-42.0KF (mol. %) eutectic salt and the typical microstructure was studied. Weibull theory was used to analyze the critical defects that caused the tensile fracture, and the microstructure of fibers before and after corrosion was characterized. It is concluded that the decrease of tensile strength after corrosion at 800 °C is caused by the surface injury of fibers, which led to the shift of critical defects from the internal defects of virgin fibers to surface defects. Moreover, corrosion at higher temperature accelerates the corrosion process and dissolve the surface O-contained layer thoroughly. This shifts the critical defects back to the internal defects and will be helpful for the recovery of tensile strength of corroded fibers at the higher temperature.     

Performance improvement of conventional and inverted polymer solar cells with hydrophobic fluoropolymer as nonvolatile processing additive

The morphology of the photoactive layer critically affects the performance of the bulk heterojunction polymer solar cells (PSCs). To control the morphology, we introduced a hydrophobic fluoropolymer polyvinylidene fluoride (PVDF) as nonvolatile additive into the P3HT:PCBM active layer. The effect of PVDF on the surface and the bulk morphology were investigated by atomic force microscope and transmission electron microscopy, respectively. Through the repulsive interactions between the hydrophilic PCBM and the hydrophobic PVDF, much more uniform phase separation with good P3HT crystallinity is formed within the active layer, resulting enhanced light harvesting and improved photovoltaic performance in conventional devices. The PCE of the conventional device can improve from 2.40% to 3.07% with PVDF additive. The PVDF distribution within the active layer was investigated by secondary ion mass spectroscopy, confirming a bottom distribution of PVDF. Therefore, inverted device structure was designed, and the PCE can improve from 2.81% to 3.45% with PVDF additive. Our findings suggest that PVDF is a promising nonvolatile processing additive for high performance polymer solar cells.     

Luminescence and scintillation properties of rare-earth-doped LuF3 scintillation crystals

The Nd-doped and Er-doped LuF₃ single crystals were grown by the micro-pulling-down method to study their scintillation properties in the vacuum-ultraviolet (VUV) region. The doubly Nd–Er codoped single crystal was grown to study possibility of scintillation performance improvement by energy transfer from Er³⁺ to Nd³⁺ ions. The LiF flux was to avoid phase transition below melting temperature. The 1%Nd-doped sample showed the highest overall scintillation efficiency under X-ray excitation which was 7 times as high as that of the LaF₃:Nd 8% standard. The leading Nd³⁺ 5d–4f emission was situated at 176 nm, while the Er³⁺ 5d–4f emission for Er-doped samples was observed at 163 nm, which better matches the sensitivity of some VUV-sensitive photodetectors. The optimum Er concentration was determined to be around 1–3 mol%. No Er³⁺ 5d–4f emission was observed for the doubly Er,Nd-codoped sample due to energy transfer from the Er³⁺ to Nd³⁺ ions. Slight improvement of the light yield was observed in the doubly-doped sample with respect to the Nd-only doped one.