Subsurface investigation of the surface modification of polydimethylsiloxane by 172‐nm vacuum ultraviolet irradiation using ToF‐SIMS and VUV spectrometry

We investigate the mechanism of polydimethylsiloxane (PDMS) surface modification by 172‐nm vacuum ultraviolet (VUV) light. Time‐of‐flight secondary ion mass spectrometry and optical spectrometry are used to measure the chemical composition and VUV transmittance of the PDMS before and after surface modification, respectively. For modified samples of bulk PDMS, the VUV transmittance and the depth of the modified region increased with increasing VUV dose. This can be explained by the following self‐reinforcing cycle of (1) modification of PDMS by VUV light to a more silica‐like composition, (2) improvement of the VUV light transparency, and (3) deeper modification. For thin‐film samples of PDMS formed on sapphire substrates, the transmittance at 172 nm also increased with increasing VUV dose and exceeded that of sapphire in the region from 172 to 300 nm. Finally, thin‐film samples of PDMS formed on silicon substrates, which function as a VUV reflector, were also investigated. For these samples, the secondary ion depth profiles for several chemical species in the PDMS were oscillatory, probably due to the interference of the incident and reflected VUV light. These results strongly suggest that the photon energy of the VUV light plays an important role in modifying PDMS.     

Effects of a chemically modified multiwall carbon nanotubes on electro-optical properties of PDLC films

Polymer dispersed liquid crystal (PDLC) films are fabricated by well-known polymerization-induced phase separation method. In this paper, the dispersion of multi-walled carbon nanotubes (MWCNT) in liquid crystals has been enhanced by chemical modification and we have investigated their effects on the morphology, electro-optical properties and conductivity of the PDLC films. Results indicated that the threshold voltage and the saturation voltage of PDLC films decreased with the increase of the doping concentration of MWCNT or chemically modified MWCNT, because carbon nanotubes can enhance the electric field by reducing the resistivity of the medium and increasing the capacitance of the cells. It can be viewed obviously that the contrast ratio of the PDLC films doped with the chemically modified MWCNT is higher than that of the MWCNT.     

Functionalizable Stereocontrolled Cyclopolyethers by Ring‐Closing Metathesis as Natural Polymer Mimics

Whereas complex stereoregular cyclic architectures are commonplace in biomacromolecules, they remain rare in synthetic polymer chemistry, thus limiting the potential to develop synthetic mimics or advanced materials for biomedical applications. Herein we disclose the formation of a stereocontrolled 1,4‐linked six‐membered cyclopolyether prepared by ring‐closing metathesis (RCM). Ru‐mediated RCM, with careful control of the catalyst, concentration, and temperature, selectively affords the six‐membered‐ring cyclopolymer. Under optimized reaction conditions, no metathetical degradation, macrocycle formation, or cross‐linking was observed. Post‐polymerization modification by dihydroxylation afforded a novel polymer family encompassing a poly(ethylene glycol) backbone and sugar‐like functionalities (“PEGose”). This strategy also paves the way for using RCM as an efficient method to synthesize other stereocontrolled cyclopolymers.     

Non‐Oxidative Methane Conversion Using Lead‐ and Iron‐Modified Albite Catalysts in Fixed‐Bed Reactor

Raw and modified albite catalysts, including Pb/Albite and Fe/Albite catalysts, have been investigated for methane conversion to C₂ hydrocarbons under non‐oxidative conditions. Introduction of Pb to albite improved the activity and selectivity to non‐coke products. Based on characterization, it was found that Pb entered into the alkali and alkaline‐earth metal sites of albite, while partial Fe doped in the tetrahedron sites and the other loaded on the surface of albite. At the reaction temperature of 1073 K, methane gas hourly space velocity (GHSV) of 2 L·gcat^–1·h^–1, catalyst dosage of 0.25 g (300 mesh), the methane conversion catalyzed by raw albite in the fixed‐bed micro reactor exhibited a methane conversion of 3.32%. Notably, introducing a Pb content of 3.4 wt% into albite greatly enhanced the conversion of methane up to 8.19%, and the selectivity of C₂ hydrocarbons reached 99% without any coke under the same reaction conditions. While Fe‐doping could weakly heighten the methane conversion to 3.97%, and coke was formed. Thus, a comparison of Pb/Albite and Fe/Albite catalysts demonstrates that the catalytic activity of albite is mainly decided by alkali and alkaline‐earth metal sites, and lead‐modification can effectively improve the catalytic activity of albite.     

Composites of poly(L‐lactide‐trimethylene carbonate‐glycolide) and surface modified SBA‐15 as bone repair material

This work aims to develop novel composites from a poly(L ‐lactide‐co‐trimethylene carbonate‐co‐glycolide) (PLTG) terpolymer and mesoporous silica (SBA‐15) nanofillers surface modified by post‐synthetic functionalization. SBA‐15 first reacts with a silane coupling agent, γ‐aminopropyl‐trimethoxysilane to introduce ammonium group. PLLA chains were then grafted on the surface of SBA‐15 through ammonium initiated ring‐opening polymerization of L ‐lactide. Composites were prepared via solution mixing of PLTG terpolymer and surface modified SBA‐15. The structures and properties of pure SBA‐15, γ‐aminopropyl‐trimethoxysilane modified SBA‐15 (H₂N‐SBA‐15), PLLA modified SBA‐15 (PLLA‐NH‐SBA‐15), and PLTG/PLLA‐NH‐SBA‐15 composites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, N₂ adsorption‐desorption, differential scanning calorimetry, contact angle measurement, and mechanical testing. The results demonstrated that PLLA chains were successfully grafted onto the surface of SBA‐15 with grafting amounts up to 16 wt.%. The PLTG/PLLA‐NH‐SBA‐15 composites exhibit good mechanical properties. The tensile strength, Young's modulus, and elongation at break of the composite containing 5 wt.% of PLLA‐NH‐SBA‐15 were 39.9 MPa, 1.3 GPa, and 273.6%, respectively, which were all higher than those of neat PLTG or of the composite containing 5 wt.% of pure SBA‐15. Cytocompatibility tests showed that the composites present very low cytotoxicity.     

Preparation,Post‐Modification,and Antibacterial Application of Gelatin Electrospun Membranes

Two bis(diaryldiazomethane)s substituted with amino groups are synthesized and used for the surface modification of membranes electrospun from gelatin. These membranes are then reacted with tolylene‐2,4‐diisocyanate to give urea‐functionalized materials, so that hydrogen peroxide can be reversibly bound onto their surface. These membranes are characterized by scanning electron microscopy, XPS, differential scanning calorimeter, and tensile test to show their surface properties and bulk properties. The surface modification with amino‐substituted diazomethanes and the subsequent cross‐linking reaction with diisocyanates contribute to high loadings of hydrogen peroxide, and greatly increase the antibacterial activity of gelatin‐derived membranes, which open a new horizon in the preparation of high loading antiseptic/antibacterial biomacromolecular surfaces and interfaces.     

石墨烯材料生物降解的策略研究

自2004年被发现以来,前沿新材料石墨烯及其衍生物由于其独特的电学、光学和力学性能被广泛关注,在许多领域都展露了光彩,包括新型电池、传感器、新能源和生物医学等领域,尤其在生物医药领域发展迅速.石墨烯及其衍生物良好的生物相容性使其在生物领域中具有重要的应用前景.为了实现石墨烯材料的体内应用,材料的可降解性是值得深入研究的焦点,研究其生物降解行为有助于提高其对环境、生命系统的安全性.到目前为止,石墨烯的生物降解研究主要集中在材料的生物酶促降解,利用一系列方法如异质原子掺杂、表面功能化修饰等对石墨烯材料进行改性,可以调控石墨烯材料的降解.综述了近年来石墨烯材料及其衍生物在生物应用上的降解的研究进展,重点介绍石墨烯的酶促降解和其在生物医学领域的应用前景,为进一步促进石墨烯材料的体内研究提供重要的研究基础和指导意义.     

氧化铈改性多级孔Hβ分子筛催化对二甲苯与苯乙炔烯基化反应（英文）

烯基芳香化合物是重要的精细化学品及中间体,在医药、染料、农药、香料、新型高分子材料和天然产品等化学工业领域得到广泛应用.传统工艺采用芳香化合物与烯基化合物的反应合成烯基芳香化合物.但是,传统过程存在许多不足:(1)芳环需预活化,如卤代等;(2)伴生氢卤酸等废物,污染环境;(3)原子经济性差.因此,研究烯基芳香化合物的清洁、高原子经济性合成备受关注.采用芳香化合物与炔基化合物的烯基化,可以100%原子经济性地合成烯基芳香化合物,且芳环无需预活化,不产生废弃物.因此,通过芳香化合物与炔的烯基化路线来合成烯基芳香化合物引起了人们的极大兴趣.尤其是固体酸催化烯基化,工艺成本低,清洁无污染,颇具工业前景.然而,固体酸催化烯基化不同于烷基化,烯基阳离子稳定性很差,比碳正离子易于聚合,进而导致催化剂积碳失活.微孔沸石分子筛用于烯基化存在底物适用范围窄、催化效率低、选择性差和炔聚合严重的问题.本研究组开展了硫酸化的镧锆氧化物介孔固体超强酸、担载磷钨酸介孔固体酸催化烯基化.采用前者,合成有序的介孔镧锆氧化物较为困难;而采用后者,催化剂的再生需要大量有机溶剂,会造成环境污染.硅铝分子筛固体酸易于制备,且可以通过简单的焙烧来再生.多级孔分子筛具有微孔分子筛和介孔分子筛的双重优势,用于烯基化反应可望获得良好效果.本文采用碱、酸对商业微孔β沸石分子筛进行处理,通过脱硅、脱铝过程来合成多级孔β分子筛,并进行稀土金属铈改性,从而制备了氧化铈改性的多级孔β分子筛,研究了其催化对二甲苯与苯乙炔的烯基化反应.通过改变碱浓度和酸浓度,对所制备的多级孔β分子筛的织构性质和酸性质进行调控,在优化的条件下获得了良好的烯基化催化性能,得到95.8%的苯乙炔转化率和95.1%的目标产物α-2,5-二甲苯基苯乙烯的选择性,总的烯基化产物(α-和β-烯基芳香化合物)的选择性达到98%.相对于微孔β分子筛,所制备的多级孔β分子筛展示了显著增强的催化活性和稳定性,目标产物选择性也有所提高.显著提高的催化性能归因于多级孔分子筛的传质强化和酸性位的增多.氧化铈的改性使得多级孔β分子筛的弱、中等和强酸中心的数目减少,可能源于减少了表面暴露的B酸位,从而导致了催化稳定性的显著提高.可见,本文所制备的氧化铈改性多级孔β分子筛用于烯基化反应具有一定前景.     

通过SAPO-34分子筛笼中引入金属物种提升甲醇制烯烃反应中乙烯选择性

低碳烯烃(乙烯、丙烯)是化学工业极其重要的基本原料.甲醇制烯烃(MTO)反应是重要的烯烃生产石油替代路线.其中,磷酸硅铝类SAPO-34分子筛在MTO反应中表现出优异的低碳烯烃选择性.与丙烯相比,乙烯具有更高的经济附加值,因此提升MTO反应中乙烯的选择性有着重要的意义.本文采用传统离子交换法(CIE)、模板辅助离子引入法(TII)和醇相离子交换法(AIE)对SAPO-34分子筛进行金属Zn、Cu改性,利用多种表征手段对金属Zn、Cu改性SAPO-34分子筛的物理结构、化学组成、金属物种状态与分布、酸性及扩散性质等进行表征.首先,对金属Zn、Cu改性SAPO-34分子筛的物理结构和化学组成进行分析.X射线衍射表明,相比AIE法,CIE法和TII法改性基本保持SAPO-34分子筛的结晶度.X射线荧光分析表明,相比Co、Ni,金属Zn、Cu更易引入SAPO-34分子筛.N2物理吸附-脱附表明,CIE法改性能够保持SAPO-34分子筛的BET比表面积和微孔孔容.其次,考察了金属Zn、Cu改性SAPO-34分子筛中金属物种的状态.氢气-程序升温还原(H2-TPR)和X射线光电子能谱(XPS)结果表明,Zn物种主要以孤立态的Zn2+阳离子形式存在.H2-TPR、XPS、紫外-可见光谱和电子顺磁共振谱结果表明,Cu物种主要以孤立态的Cu2+阳离子以及部分CuO形式存在.继而对金属Zn、Cu改性SAPO-34分子筛中金属物种的分布进行表征.XPS表明,Zn阳离子改性的SAPO-34表层富硅、富Zn,呈类核壳结构;XPS和扫描式电镜-能量色散X射线光谱结果表明,Cu物种在Cu改性SAPO-34分子筛中均匀分布.进一步研究了金属Zn、Cu改性SAPO-34分子筛中酸性的变化.氨气-程序升温脱附和核磁共振氢谱结果表明,Zn、Cu改性SAPO-34酸性位点的酸量降低.最后,对金属Zn、Cu改性SAPO-34分子筛的扩散性质进行分析.智能重量分析表明,Zn、Cu阳离子的引入降低探针分子(乙烷、丙烷)的扩散系数,推断Zn、Cu阳离子的引入增加对MTO反应产物的扩散限制.热重表明,Zn阳离子改性SAPO-34分子筛反应初期积炭量略微增加.综上所述,Zn阳离子改性SAPO-34催化剂表层富硅、富Zn,呈现类核壳结构.Zn阳离子的引入增加对MTO反应产物的扩散限制,而且Zn阳离子的引入促进MTO反应初始阶段的碳沉积.因此,Zn阳离子改性SAPO-34分子筛显著增加MTO反应产物的扩散限制,对分子尺寸较大的反应产物的扩散限制更为明显,从而提高MTO反应初始阶段的乙烯选择性,增大乙烯/丙烯比.     

Visible light-induced thione-ene cycloaddition reaction for the surface modification of polymeric materials

A feasible method for the surface modification of polymeric materials with LDPE films as model substrates based on visible light-induced thione-ene cycloaddition reaction is proposed.