Stark absorption spectroscopy of indole and 3-methylindole

Indole and 3-methylindole (3-MI) doped into a polymethylmethacrylate (PMMA) film are studied by the Stark absorption (electroabsorption) spectroscopy. The 1La and 1Lb absorption bands are distinguished and the change in permanent dipole moment on 1La excitation is determined by a model fit to the measured absorption and electroabsorption spectra. Analysis of the spectra, measured at normal incidence and magic angle conditions, proved the essential role of the electric-field-induced orientation/alignment effects for polar indole and 3-MI molecules in the PMMA environment at room temperature.     

Growth of organic n-conductors on thin polymer films for use in organic field effect transistors

Thin films of different polymers - poly(styrene) (PS), poly(methylmethacrylate) (PMMA), poly(vinylcarbazole) (PVCz), poly(vinylchloride) (PVC) and poly(vinylidene fluoride) (PVDF) - were deposited by spin-coating or by vapor deposition. On these polymers, thin films of (hexadecafluorophthalocyaninato)-oxovanadium (F₁₆PcVO) were prepared by physical vapor deposition. The growth of these films was monitored in situ by optical spectroscopy. The optical absorbance spectra were analyzed based on the coupling of transition dipoles to obtain information on the intermolecular arrangement of chromophores in the films. In all of these samples, the molecules are oriented with their molecular plane preferentially perpendicular to the substrate surface. This gives the desired overlap of the π-systems for electric conductance parallel to the substrate. Differences in the interactions were detected when deposition temperatures below or above the glass transition temperature of a given polymer were compared. The morphology of the polymer films and the deposited semiconductors were investigated by atomic force microscopy and scanning electron microscopy. The influence of the chosen substrate on the film structure is determined. The optical and electric properties of the films could thereby be influenced and the applicability of such films as active layers in organic thin film transistors is discussed.     

High breakdown strength and low loss binary polymer blends of poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) and poly(methyl methacrylate)

Dielectric materials with high breakdown strength and low loss are of crucial importance in capacitive energy storage electronics. Herein, a kind of polymer blend composed of poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) ferroelectric terpolymer and linear dielectric poly(methyl methacrylate) (PMMA) is presented. The polymer blend shows a breakdown strength of 733 MV/m and a charge‐discharge efficiency over 90% at 200 MV/m with optimized PMMA content, which are 101% and 28% higher than that of neat terpolymer. Moreover, microsecond discharge time of 2.26 μs, along with a power density that is 3.6 times that of the current commercially available biaxially oriented polypropylene, as well as great cyclic performance, has been achieved under an electric field of 200 MV/m. The findings of this research demonstrate that the incorporation of linear dielectric PMMA into poly(vinylidene fluoride)‐based ferroelectric polymer provides a new strategy in designing high breakdown strength low loss dielectric materials for reliable compact flexible film capacitors.     

Optical Spectra of Polygermane/Mesoporous Silica Nanocomposites

Summary: The monitoring of poly(di-n-hexylgermane) (PDHG) optical spectra in a variety of structures ranging from a bulk film to a nanosize polymer confined into a nanopore of SBA-15 was performed using the fluorescence and fluorescence excitation spectra in the temperature range from 5 to 240 K as well as the absorption and FTIR spectra at room temperature. The observed data were compared with those obtained for poly(di-n-hexylsilane). It was shown that PDHG film absorption and fluorescence spectra strongly depend on the polymer thickness and consist of a number of bands which were assigned to centers with different amount of trans- and gauche- conformers of the polymer chains. Conformations of the polymer chains found in a thin film and in a 10 nm pore are similar while differing from the conformations of a thick film. Optical spectra of the confined PDHG are blue-shifted relative to those of a thin film. The PDHG polymer chain conformation becomes disordered with the decrease of the polymer film thickness and the nanopore size from 10 to 6 nm.     

Theoretical foundation of electroabsorption spectroscopy: Self-contained derivation of the basic equations with the direction cosine method and the Euler angle method

Self-contained derivation of the electroabsorption (E-A, Stark effect) equations of Liptay and Czekalla, which describe the external electric field effects on absorption spectra of a mobile ensemble of light-absorbing molecules at thermal equilibrium, is reported. Two mathematically different ways for obtaining the ensemble averages, the “direction cosine method” and the “Euler angle method”, are compared. Some examples illustrating the application of E-A equations in the analysis of electroabsorption spectra are presented.     

Thermal and photo-induced phenomena in γ-irradiated poly(methyl methacrylate)

ESR spectra and optical absorption spectra of γ-irradiated poly(methyl methacrylate) (PMMA) at 77°K and the photo- and thermal bleaching behavior have been studied. γ-Irradiation of PMMA yields a singles spectrum with a line width of 6 G which is bleachable with visible light. This species is assigned to the polymer cation. The unbleached species consists mainly of a four-line spectrum and is assigned to a polymer radical having a different CH₂ conformation from the usual nine-line spectrum. On subsequent warming to room temperature, the spectrum changes into the nine-line spectrum. γ-Irradiation of PMMA containing biphenyl as an additive at 77°K gives biphenyl cation. Yield of polymer radical is reduced by the addition of biphenyl and 2-methyltetrahydrofuran. A mechanism is proposed which is consistent with the experimental results.     

External electric field effects on fluorescence of pyrene butyric acid in a polymer film: concentration dependence and temperature dependence

Fluorescence spectra and electrofluorescence spectra (plots of the electric field-induced change in fluorescence intensity as a function of wavelength) have been measured at different temperatures for pyrene butyric acid (PBA) in a PMMA film at different concentrations. At a low concentration of 0.5 mol % where fluorescence emitted from the locally excited state of PBA (LE fluorescence) is dominant, LE fluorescence spectra show only the Stark shift in the presence of an electric field (F), which results from the difference in molecular polarizability between the ground and emitting states. At a high concentration of 10 mol % where the so-called sandwich-type excimer fluorescence (EX(1)) is dominant, both EX(1) and LE fluorescence are quenched by F. Another fluorescence assigned to a partially overlapped excimer (EX(2)) also exists at room temperature, and this emission is enhanced by F. As the temperature decreases, three fluorescence emissions whose electric field effects are different from each other become clear besides EX(1) and LE fluorescence, indicating that at least five fluorescence components exist at high concentrations at low temperatures. At a medium concentration of 5 mol % where EX(1) is comparable in intensity to the LE fluorescence, the intensity of EX(1) is not affected by F at any temperature, but LE fluorescence and EX(2) are markedly influenced by F at room temperature, and four fluorescence emissions are confirmed at low temperatures.     

单色化X射线对薄膜表面高分子降解行为的影响

采用聚甲基丙烯酸甲酯(PMMA)和苯乙烯-丙烯腈无规共聚物(SAN)薄膜体系, 在不同的实验温度下, 研究了单色化的X射线对其中一个组分(PMMA)降解行为的影响.     

Fluorescence characteristics and photostability of benzoxazole derived donor-acceptor dyes in constrained media

The spectroscopic properties and photoreactivity of 2-(4-dimethylaminostryl)benzoxazole and its butadienyl analogue (abbreviated as DMASBO and BODB, respectively) were investigated in thin films of PS, PMMA and PVA polymer matrices as well as immobilized on silica surface. The experimental results showed that the investigated benzoxazole derivatives are sensitive to the polarity of its microenvironment even in the glassy matrices and in the solid state. The micropolarity of PVA and silica surface is greater than that of PMMA and PS. The combined results of fluorescence quantum yield and photoisomerization indicated that the size of the free volume within the polymer matrix influence strongly the photochemical reactivity of the used dyes. In PVA, which offers the smaller free volume, the photoreaction is totally blocked while the fluorescence yield is extremely enhanced relative to those in solutions and other polymer matrices. This is associated with an emission of green laser from DMASBO-PVA doped film when pumped by nitrogen laser (337 nm). The results showed that the present dyes are excellent probes for non-fluorescent systems presenting constrained geometry. The spectra of amorphous solid thin films of both dyes were also measured and show large red shifts relative to those in solutions indicating symmetric aggregation of molecules in the solid crystals.     

Edge-excitation red shift of the fluorescence of flexible solute molecules in a poly(methyl methacrylate) polymer matrix

An excitation wavelength dependence of the fluorescence of tert-butyl and methyl esters of 9-anthroic acid and of tetraphenylbutadiene and tetraphenylmethylbutadiene in a poly(methyl methacrylate) (PMMA) polymer matrix is explained in terms of the presence of conformers that experience different free volumes at 77 K relative to room temperature.     

Photo‐alignment material with azobenzene‐functionalized polymer linked in film

Application of a new azo‐polymer as a photo‐alignment material for liquid crystals (LCs) was demonstrated. 4‐(Vinyloxyethyloxy)azobenzene (VAZO), which has thermally reactive vinyl ether groups, reacted with the ? OH groups of poly(4‐hydroxystyrene) (PHS) during the baking process. The azo‐attached polymer (PHS‐VAZO) film showed anisotropic spectra after exposure to 365‐nm linear polarized light (LPL) unlike the VAZO‐doped poly(methylmethacrylate) (PMMA) film. The anisotropy of the film was small at high concentration of the azo‐chromophore because of thermal randomization of the polarized state. In the evaluation of photo‐alignment of the LC, the LC hybrid cell using the PHS‐VAZO film achieved high LC alignment. The azo‐attached polymer using the thermal reaction of vinyl ethers is useful for a photo‐alignment material. Copyright © 2002 John Wiley & Sons, Ltd.     

电场条件下高分子共混物组分浓度梯度化的研究

研究了聚乙烯醇/聚丙烯酸高分子共混物水溶液中,共混物各组分在电场诱导条件下沿电场方向的浓度梯度分布情况.通过测定不同时刻PVA/PAA高分子共混物水溶液在电场的不同区域内的pH值,研究了电场诱导下共混物各组分沿电场方向的迁移过程.结果表明,PAAn-向电场正极迁移,同时由于浓差梯度,PVA向负极迁移,并形成浓度梯度分布.随时间的延长,高分子共混物的组分梯度程度逐渐加大.     

Electron irradiation induced microstructural modifications in BaCl2 doped PVA: A positron annihilation study

Thin films of pure and 10 wt% BaCl₂ doped poly(vinyl alcohol) (PVA) were prepared by solution casting method. These films were subjected to electron irradiation for different doses ranging from 0 to 400 kGy in air at room temperature. The effect of electron irradiation on the optical and free volume related microstructures of these polymer films was studied using positron annihilation lifetime spectroscopy, FTIR and UV-vis techniques. The FTIR spectral studies indicate that the electron irradiation induces chemical modifications within the doped PVA, which results in chain scission as well as cross-linking of the polymer. The positron lifetime study on these irradiated polymers shows that the chain scissions and cross-linking within the polymer matrix affect the free volume content and hence the microstructure. The UV-vis optical absorption studies show that the induced microstructural change by electron irradiation also modifies the optical properties. Using UV-vis spectra, the optical energy band gap was estimated and it decreases with increase in electron dose. A correlation between positron results and optical results is obtained and electron irradiation induced microstructure modifications within the doped polymer are understood. The results highlight the usefulness of positron annihilation technique in the study of the microstructure of irradiated polymers.     

Synthesis and Characterization of a Diblock Copolymer of Methyl Methacrylate and Vinyl Acetate by Successive Photo‐Induced Charge Transfer Polymerization Using Ethanolamine as the Parent Compound

Communication: A diblock copolymer consisting of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) with hydroxyl group at one end is prepared by successive charge transfer polymerization (CTP) under UV irradiation at room temperature using ethanolamine and benzophenone as a binary initiation system. The diblock copolymer PMMA‐b‐PVAc could be selectively hydrolyzed to the block copolymer of poly(methyl methacrylate) and poly(vinyl alcohol) (PVA) using sodium ethoxide as the catalyst. Both copolymers, PMMA‐b‐PVAc and PMMA‐b‐PVA, are characterized in detail by means of FTIR and ¹H NMR spectroscopy, and GPC. The effect of the solvent on CTP and the kinetics of CTP are discussed.     

Optical properties of Rh 6G dye in liquid and solid polymer

Rhodamine 6G dye doped in liquid MMA (monomer) and solid polymer (PMMA) has been studied and its spectra compared with the one dissolved in n-BA solvent. The effect of temperature and laser power on the emissive characteristics of dye in polymer and in solvent has also been compared.     

Oriented polymer dispersed discotic liquid crystals

Polymer dispersed discotic liquid crystals (PDDLCs) were prepared using the hexa-n-octanoate of rufigallol (RHO) and three polymer matrices: polystyrene (PS), poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA). The molecular orientation of RHO in stretched PDDLC films was characterized by means of infrared dichroism. It was found that the stretching of films that contain RHO in both the columnar D1 and crystalline phase can effectively align columns of RHO along the stretching direction, with the short axes of the rigid cores lying in the plane of the film. By contrast with stretched polymer dispersed nematic liquid crystals, no orientation of RHO is induced for films stretched with RHO in the isotropic phase, followed by rapid cooling to room temperature. However, if stretched films are cooled under strain into the columnar D1 phase, orientation of RHO can develop with time.     

Oriented polymer dispersed discotic liquid crystals

Polymer dispersed discotic liquid crystals (PDDLCs) were prepared using the hexa-n-octanoate of rufigallol (RHO) and three polymer matrices: polystyrene (PS), poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA). The molecular orientation of RHO in stretched PDDLC films was characterized by means of infrared dichroism. It was found that the stretching of films that contain RHO in both the columnar D1 and crystalline phase can effectively align columns of RHO along the stretching direction, with the short axes of the rigid cores lying in the plane of the film. By contrast with stretched polymer dispersed nematic liquid crystals, no orientation of RHO is induced for films stretched with RHO in the isotropic phase, followed by rapid cooling to room temperature. However, if stretched films are cooled under strain into the columnar D1 phase, orientation of RHO can develop with time.     

Total‐reflection X‐ray diffraction study of friction‐transferred poly(tetrafluoroethylene) film

The orientational structure of the friction‐transferred poly(tetrafluoroethylene) (PTFE) film, which consists of highly oriented polymer strands, was evaluated with energy‐dispersive total‐reflection X‐ray diffractometry. In the film, each PTFE molecule is oriented along the friction direction, and PTFE crystallites have a preferred orientation with respect to the substrate surface. The orientational distribution of the chain direction was quantitatively evaluated. The half‐width of the distribution was determined to be about 3°. The dependence of the orientational distribution on temperature is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 432–438, 2001     

掺杂多壁碳纳米管改性聚溴甲酚绿膜修饰电极的制备、表征与应用研究

研究了掺杂多壁碳纳米管(MWNT)改性聚溴甲酚绿膜(PBG),以不同修饰方法制备了4种修饰电极,用扫描电镜、交流阻抗及循环伏安法等对电极进行表征。结果表明:4种修饰电极的电活化面积均得到明显提高,其中以层层修饰制备的聚溴甲酚绿膜/多壁碳纳米管复合膜(PBG/MWNT/GC)电极最能发挥MWNT和PBG的电活性。将电极用于8-羟基喹啉(8-HQ)电化学行为的研究,结果表明:4种修饰电极的伏安响应明显提高,且8-HQ在PBG/MWNT/GC上的氧化峰电位负移最多,峰电流最大,约为裸玻碳电极的4.5倍,电催化作用显著增强。8-HQ在PBG/MWNT/GC上电极反应的电子转移数和质子数均为1,是吸附控制的不可逆电氧化过程,氧化峰电流Ip与浓度c在4.0×10-6～3.5×10-4mol/L范围内呈良好的线性关系,r=-0.997 2,检出限(S/N=3)为1.96×10-8mol/L。PBG/MWNT/GC修饰电极可实现8-HQ的快捷、简便测定。     

Optical properties of polymer blends composed of poly(methyl methacrylate) and ethylene–vinyl acetate copolymer

Optical properties for immiscible polymer blends composed of poly(methyl methacrylate), PMMA, and ethylene–vinyl acetate copolymer (EVA) are studied employing various EVA samples with different vinyl acetate contents. PMMA/EVA shows transparency at room temperature when the difference in refractive index between both phases is small. The light transmittance, however, decreases with increasing the ambient temperature. This phenomenon is attributed to the difference in the volume expansion ratio, leading to the difference in refractive index, between PMMA and EVA. It is found that addition of tricresyl phosphate, TCP, improves the transparency and its temperature dependence. As a result, a ternary PMMA/EVA/TCP blend shows high level of transparency in the wide temperature range, although it has apparent phase separated morphology.