准一维共聚物的电子结构研究

在紧束缚近似下,建立了共聚物 (- PPP_x )—( PA_y)- 的物理模型,研究了组成共聚物的均聚物单体对体系晶格结构、能带结构等的影响,发现共聚物的带隙可通过改变均聚物的配比或均聚物之间的相互作用来加以调制. 关键词： 共聚物 界面耦合 带隙     

一维共聚物链的色散关系研究

研究了一维共聚物链的晶格振动，得到了不同均聚物构型的色散关系，并分析了其振动模的结构特点.调整界面耦合，得到了界面模，其频率位于声频与光频或光频之间的带隙中.从晶格振动的角度分析了共聚物的量子阱或超晶格特征. 关键词： 共聚物 界面耦合 晶格振动     

13C及29Si核磁共振研究苯乙烯-二甲基硅氧烷嵌段共聚物的弛豫及分子运动

用¹³C及²⁹Si核磁共振研究了苯乙烯(S)及二甲基硅氧烷(Si)嵌段共聚物中硅氧烷软段的固体及溶液谱的自旋-晶格弛豫时间T₁。固态嵌段共聚物主链²⁹Si及侧甲基¹³C的T₁都与均聚物的T₁相近,但在CdCl₃溶液中各种嵌段共聚物的T₁与均聚硅氧烷相差颇大。用偶极-偶极相互作用来解释高聚物的自旋-晶格弛豫。苯乙烯-二甲基硅氧烷嵌段共聚物具两相结构,所以嵌段共聚物中软段及硬段微区中链段的运动与在均聚物分子中链段的运动模式基本相同。而CdCl₃对聚苯乙烯或聚硅氧烷都是良溶剂,软段硬段之间有相互影响。所以其链段运动与均聚物不同,从而导致链段运动的相关时间τ_c变短和T₁的增长。     

聚对苯二甲酸丁二醇酯/聚(对苯二甲酸丁二醇酯-e-己内酯)二元结晶共混体系的相容性和结晶行为

聚对苯二甲酸丁二醇酯(PBT)/聚(对苯二甲酸丁二醇酯-e-己内酯)(PBT-PCl)是一个新制备的具有分子间排斥相互作用的A/AxB1?x型两元结晶共混体系. 根据两元平均场模型,报道对苯二甲酸丁二醇酯(BT)与"-己内酯(CL)结构单元的相互作用参数为0.305. DSC研究发现,此共混物呈现了与典型的共聚物/均聚物共混物不同的结晶特征. PBT-PCL影响PBT链的活动力和晶片堆积;同时PBT-PCL的结晶受到先期结晶的PBT晶粒的阻滞. 尽管拥有相同的BT单元,共混的两组分在组成变化范围内仍没有形     

三嵌段共聚物的电子结构及态密度特征

采用紧束缚近似计算方法,针对小带隙的聚乙炔(polyacetylene,(PA))和大带隙的聚对苯撑(poly(p-phenylene),(PPP)组成的三嵌段共聚物(triblock copolymer)-(PA)x-(PPP)n-(PA)y-和-(PPP)x-(PA)n-(PPP)y-性质进行了研究,发现它们具有典型的量子阱特征.对均聚物PPP和PA以及三嵌段共聚物的态密度(density of states, (DOS))进行了计算分析,发现共聚物的态密度与均聚物的态密度有着显著的区别,共聚物的带隙的大小介于大带隙的PPP和小带隙的PA之间,在共聚物中与PPP的导带和价带的子带隙以及共聚物的导带底和价带顶中,所存在的能态密度只能由PA来提供,而在共聚物的价带底和导带顶的能态密度则取决于PPP的态密度.     

红外光谱法测定聚(乳酸-苯丙氨酸)共聚物的含量

分别以苯丙氨酸和乳酸为原料合成了3-苯甲基-2,5-吗啉二酮(PMD)与丙交酯(LA),以PMD和LA作为聚合单体经开环聚合分别得到PMD均聚物(PPMD)、丙交酯均聚物(PLA)及聚(乳酸-苯丙氨酸)共聚物。对合成的均聚物进行红外分析,确定1 671.53和870.82 cm-1处的吸收峰分别为PPMD和PLA的特征峰。根据以上两种特征吸收峰并以朗伯-比耳定律为理论依据,建立了利用红外光谱法测定聚(乳酸-苯丙氨酸)共聚物含量的方法。实验测定的标准工作曲线为y=0.055 67x+0.1091,r=0.999 3。利用该标准工作曲线定量测定了共聚物组分含量,其结果与1H NMR测定值一致,相对误差在2％以内,证明红外光谱法可方便、快捷地测定聚(乳酸-苯丙氨酸)共聚物组分含量,且适用于其他聚(乳酸-氨基酸)共聚物的含量测定,具有一定的实用性及推广性。     

PET与SAN/PAN复合膜界面的 FTIR-ATR研究

应用傅里叶衰减全反射红外光谱(FTIR-ATR)技术对聚对苯二甲酸乙二酯(PET)表面形成不同厚度的超薄苯乙烯-丙烯腈共聚物(SAN)和聚丙烯腈(PAN)的共混物膜及其SAN/PAN共混物膜的厚度、界面层PET亚甲基的构像变化等进行研究,结果表明PET表面共混物膜的厚度随共混物混合液中SAN含量的增加而增加,界面层成膜物质与基材的分子链段间发生了相互渗透和扩散,分子链的极性越相近,越容易成膜.对PET红外光谱吸收峰的A1340/A1410进行定量研究表明,在成膜过程中,PET分子链的亚甲基构像由反式向旁式转变,引起界面层PET的结晶度降低.FTIR-ATR是分析复合膜界面层结构信息的有效方法.     

无规共聚物与均聚物共混体系的相容性

用核磁共振方法(NMR)及差示扫描量热法(DSC)测定了苯乙烯-丙烯腈(SAN)无规共聚物与均聚物系列聚甲基丙烯酸甲酯(PMMA),聚甲基丙烯酸乙酯(PEMA),聚甲基丙烯酸正丁酯(PnBMA),聚甲基丙烯酸异丁酯(PiBMA)共混体系的有关参数,比较全面地研究了影响SAN与聚甲基丙烯酸酯类(PMAs)相容性的因素,对它们相容性的本质进行了探讨,得出了一些重要结论.     

聚（偏二氟乙烯-三氟乙烯）压电圆管水听器

提出了高灵敏度压电共聚物圆管水听器设计方法,论述了聚(偏二氟乙烯-三氟乙烯)[P (VDF-TrFE)]材料结构与压电特性的关系,利用解析法和有限元法,分析了多振动模式耦合特性对压电共聚物圆管水听器灵敏度响应的影响规律,仿真分析了圆管水听器的耐静水压特性和噪声特性,与相同结构的压电陶瓷和压电均聚物水听器相比,压电共聚物圆管水听器低频段灵敏度分别可提高20 dB和5 dB以上,研制了尺寸为Φ14 mm × 55 mm的压电共聚物圆管水听器样品,经测试,在10 Hz~1 kHz频段内水听器灵敏度响应达到-181.8 dB±1 dB,等效自噪声压低于零级海况海洋环境噪声,与理论模型结果有良好的一致性。结果表明,该设计显著提升了圆管水听器的低频接收灵敏度,并为其耐静水压性能提升提供了思路。      

一维导电共聚物中极化子输运的动力学研究

利用非绝热动力学方法,理论上研究了一维导电共聚物[-(PT)x-(PPP)y]z-(PT)x-中的极化子在外电场作用下的动力学输运性质.研究发现,极化子在共聚物中不易传输,其运动敏感地依赖于嵌段间界面的耦合;嵌段尺度对于极化子的运动具有重要的影响.所得结果与相关实验一致.     

Electronic confinement in quasi—one—dimensional triblock copolymers

A tight-binding calculation to describe the triblock copolymer xPA(polyacetylene)/nPPP (poly(p-phenylene))/yPA or xPPP/nPA/yPPP is presented. The interfacial coupling between homopolymer segments is attributed to the hopping of π-electrons and the coupling of σ-bonds. The dependence of the band gap of triblock copolymers on the interfacial couplings or on the composite segment lengths is studied. The influence of composite segment lengths on the electron density is also studied. For nPPP/xPA/nPPP structures, the band gap varies with PA segment length over a wide range of 1.32－2.74eV. For nPA/xPPP/nPA structures,the band gap is invariant with PPP segment length. It is found that a spontaneous tunnelling phenomenon could take place in nPA/xPPP/nPA structures. Furthermore, the polaron caused by doping an electron into nPA/xPPP/nPA will tend to be confined in one of the well (PA) parts. This kind of confinement may increase the electron－hole recombination probability.     

Influence of Grafting Density of Diblock Copolymers on Interfacial Assembly Behavior and Interfacial Shear Strength of Glass Fiber/Polystyrene Composites

To investigate the influence of the grafting density and the molecular structure of block copolymers on the interfacial assembly behavior and interfacial shear strength, macromolecular coupling agents, hydroxyl-terminated poly(n-butyl acrylate-b-styrene) (HO-P(BA-b-S)) were synthesized by atom transfer radical polymerization, and then chemically anchored on the glass fiber surfaces to form a well-defined monolayer. The phase separation and 'hemispherical' domain morphologies of diblock copolymer brushes at the polystyrene/glass fiber interface were observed. The interfacial assembly morphology differs with changes in the grafting density of diblock copolymers. When the grafting density is greatest, the highest height difference of the hemispherical domain and the largest surface roughness are achieved, as well as the best interface shear strength. It was also found that the copolymer brush with a PBA block of the polymerization degree (Xn) about 77 is the optimal option for the interfacial adhesion of PS/GF composites. Thus, the grafting density and molecular structure of diblock copolymers determines the interfacial assembly behavior of copolymer brushes, and therefore the interfacial shear strength.     

An estimation of the magnetic disorder at Fe/Cr interfaces in coupled and non-coupled Fe/Cr multilayers

The antiferromagnetic coupling at the Fe/Cr interfaces, inferred from the orientation of the Cr magnetic moments, is used to estimate the magnetic disorder resulting from the interfacial roughness in Fe/Cr multilayers. A crossover from in-plane to out-of-plane orientation of Cr moments depends on the energy cost in either case: (i) to break the interfacial Fe–Cr antiferromagnetic coupling or (ii) having sites with frustrated Cr–Cr antiferromagnetic coupling in the Cr interlayers. A quantitative model of the magnetic frustration due to interfacial disorder in Fe/Cr multilayer systems is described. The step edge density, or terrace size, required to break the interfacial Fe–Cr coupling and destroy the Fe–Fe interlayer exchange coupling is estimated.     

Electronic and Optical Properties of Some Polysulfone-Polydimethylsiloxane Copolymers in Thin Films

Polysulfone (PSF)-polydimethylsiloxane (PDMS) block copolymers (PSF-b-PDMS) with various compositions were prepared by condensing chloro-terminated polysulfone oligomers with α, ω -dihydrogensilyl-polydimethylsiloxane in refluxing chlorobenzene solution in the presence of urea as a hydrogen chloride acceptor. The temperature dependences of the electrical conductivity and thermoelectric power (Seebeck coefficient) of copolymers were studied using thin films deposited from a dimethylformamide solution (spin coating method) onto glass substrates. It was established that the various copolymers showed typical semiconducting properties. Some correlations between these properties (activation energy, ratio of carrier mobilities, etc) and molecular structure of the copolymers were found. A model based on band gap representation was found to be suitable for explanation of the electronic transport mechanism through the studied copolymers in thin films. The study of the transmission and absorption spectra (in the spectral range from 300 nm to 1400 nm) evidenced that the indirect allowed optical transitions were predominant. The values of the optical energy band gap (ranged between 1.50 eV and 1.70 eV) are in agreement with values of width of the forbidden band calculated from the temperature dependence of the electrical conductivity.     

Energy band alignment of 2D/3D MoS2/4H-SiC heterostructure modulated by multiple interfacial interactions

The interfacial properties of MoS₂/4H-SiC heterostructures were studied by combining first-principles calculations and X-ray photoelectron spectroscopy. Experimental (theoretical) valence band offsets (VBOs) increase from 1.49 (1.46) to 2.19 (2.36) eV with increasing MoS₂ monolayer (1L) up to 4 layers (4L). A strong interlayer interaction was revealed at 1L MoS₂/SiC interface. Fermi level pinning and totally surface passivation were realized for 4H-SiC (0001) surface. About 0.96e per unit cell transferring forms an electric field from SiC to MoS₂. Then, 1L MoS₂/SiC interface exhibits type I band alignment with the asymmetric conduction band offset (CBO) and VBO. For 2L and 4L MoS₂/SiC, Fermi level was just pinning at the lower MoS₂ 1L. The interaction keeps weak vdW interaction between upper and lower MoS₂ layers. They exhibit the type II band alignments and the enlarged CBOs and VBOs, which is attributed to weak vdW interaction and strong interlayer orbital coupling in the multilayer MoS₂. High efficiency of charge separation will emerge due to the asymmetric band alignment and built-in electric field for all the MoS₂/SiC interfaces. The multiple interfacial interactions provide a new modulated perspective for the next-generation electronics and optoelectronics based on the 2D/3D semiconductors heterojunctions.     

Sorption properties of the interfacial layer in polyester-polysiloxane block copolymers (inverse gas chromatography)

The fine supramolecular structure of multiblock polyester-polysiloxane copolymers has been studied. A method is proposed for quantitatively estimating the sorption properties of interfacial layers in block copolymers, which are difficult to determine.     

Two-dimensional intrinsic ferromagnetism at nitride-boride interfaces

We predict theoretically novel two-dimensional interface ferromagnetism at AlN/MgB(2)(0001) using first-principles calculations, where the interface is employed as an ordered structure of spin sites instead of point defects. Although N dangling bonds are apparently saturated, interfacial states exhibit spin polarization. Hund's coupling of the two N p(∥) orbitals as well as low density of states at the Fermi energy contribute to strong band ferromagnetism. Furthermore, first-principles electron transport calculations demonstrate that this interfacial spin polarization is responsible for quantum spin transport. The magnetization can be controlled by applied gate bias voltages.     

Effect of interfacial coupling on rectification in organic spin rectifiers

The effect of interfacial coupling on rectification in an organic co-oligomer spin diode is investigated theoretically by considering spin-independent and spin-resolved couplings respectively. In the case of spin-independent coupling, an optimal interfacial coupling strength with a significant enhanced rectification ratio is found, whose value depends on the structural asymmetry of the molecule. In the case of spin-resolved coupling, we found that only the variation of the interfacial coupling with specific spin is effective to modulate the rectification, which is due to the spin-filtering property of the central asymmetric magnetic molecule. A transition of the spin-current rectification between parallel spin-current rectification and antiparallel spin-current rectification may be observed with the variation of the spin-resolved interfacial coupling. The interfacial effect on rectification is further analyzed from the spin-dependent transmission spectrum at different biases.     

Maleated wood-fiber/high-density-polyethylene composites: Coupling mechanisms and interfacial characterization

Chemical coupling of maleated polyethylene (MAPE) copolymers at the interface in wood-fiber/high-density-polyethylene (HDPE) composites was investigated in this study. FTIR and ESCA analyses presented the evidence of a chemical bridge between the wood fiber and polymeric matrix through esterification. The feature peak of esterification occurred in the range between 1800 and 1650 cm^?1 at FTIR spectra. Succinic and half succinic esters were the two primary covalent bonding products to cross-link the wood fiber and thermoplastic matrix. Maleated composites had a remarkable shift on most O1s and C1s spectra in respect to the wood, HDPE, and untreated composites. The binding energy of maleated composites at C1s and O1s spectra was around 282 eV and 530 eV, respectively. The mass concentration of chemical components at the interface was related to the coupling agent type, structure, and concentration. According to the FTIR and ESCA analyses, the coupling mechanisms of MAPEs were proposed. The interfacial morphology in wood-fiber/HDPE composites was illustrated with the pinwheel models based on SEM observations.