石墨烯/聚乙烯醇/聚偏氟乙烯基纳米复合薄膜的介电性能

石墨烯由于具有良好的力学性能、高的电子传递能力以及相对较低的生产成本等优势而受到广泛关注,但现在多将其直接分散在聚合物中提高聚合物的介电性能.本工作中,制备出了还原氧化石墨烯/PVA/聚偏氟乙烯(PVDF)的三相纳米复合薄膜.首先把聚乙烯醇(PVA)和氧化石墨烯(GO)分散于二甲基亚砜(DMSO)中,得到PVA非共价键修饰的GO,再将PVDF溶于该混合液体中,通过溶液浇注以及低温加热过程得到三相纳米复合薄膜.实验结果表明,在120?C下,GO可以被热还原成还原氧化石墨烯(RGO),且可以促进PVDF的α相向β相转变.PVA修饰RGO比单纯RGO在PVDF基体中分散性要好,且使PVDF的球晶尺寸大大降低,复合薄膜的介电性能大幅提高.RGO/PVA/PVDF复合膜的渗流阈值f*_(vol)约为8.45 vol.%,在10~2Hz时RGO/PVA/PVDF复合膜的介电常数大约是纯PVDF的238倍.本工作为制备介电性能高、生产成本低、操作简单的聚合物纳米复合材料提供了一种好的方法.     

聚偏氟乙烯在不同衬底上的结晶行为研究

利用滴涂法制备聚偏氟乙烯(PVDF)薄膜,分别以载玻片、铜片、聚四氟乙烯(PTEF)为衬底研究衬底、退火时间和退火温度对PVDF薄膜结晶行为的影响。实验表明PVDF在PTEF基体上更容易结晶,这是因为PTEF是非极性基体,PVDF分子链运动在界面不受限制,能够充分地重排,利于晶体的生长;延长退火时间,PVDF分子链能够充分进行重排,形成规整的结构,提高结晶性;同时提高退火温度也有利于PVDF薄膜的结晶。另外,基体作用、退火时间和退火温度不会改变PVDF晶体结构,但会不同程度地影响α和β相的含量。     

掺杂浓度与溶剂对偶氮聚合物薄膜全光开关

用重复旋转涂膜法制备了乙基红(ER)偶氮染料与聚甲基丙烯酸甲酯(PMMA)掺杂聚合物薄膜和乙基橙(EO)与聚乙烯醇(PVA)掺杂聚合物薄膜.测量了两种聚合物薄膜样品全光开关特性,比较分析了薄膜样品的掺杂浓度和溶剂对全光开关效应的影响,实验结果表明:增加掺杂浓度和溶剂,极性薄膜样品的全光开关效应增强且开关的本底信号增大,但对开关的响应速度影响很小;选择合适的掺杂浓度和强极性溶剂,在室温和几个mW的弱功率控制光条件下聚合物薄膜具有毫秒级开关响应时间和40%以上的开关调制深度,最大的调制深度达72%以上.     

POSS纳米复合物链运动的固体NMR研究

利用固体NMR技术、并结合TEM技术研究了POSS掺杂到不同聚合物体系后POSS复合物的链段运动及结构特点,其中聚合物包括聚甲基丙烯酸正丁酯（PBMA）和聚甲基丙烯酸甲酯（PMMA）. 实验结果表明：POSS能很好的分散在这2种聚合物中,形成纳米结构的复合物;其中POSS在PBMA中形成的复合物表现出较强的链段运动性,而在PMMA中则表现出较低的运动性;同时,2D HETCOR的结果表明这2种聚合物本身结构特点不同,POSS/PBMA复合物中聚合物部分与POSS部分间的距离较近,而在POSS/PMMA中则较远.     

高质量钙钛矿量子点薄膜制备及性能研究

对聚甲基丙烯酸甲酯(PMMA)和聚苯乙烯-聚乙烯-聚丁烯-聚苯乙烯嵌段共聚物(SEBS)高分子聚合物材料包裹钙钛矿量子点进行了研究.利用一步包裹法制备了高质量的钙钛矿量子点薄膜,在连续365nm紫外激发下和LED远程封装时,PMMA钙钛矿薄膜衰减率分别约是SEBS薄膜的4倍和6倍,证明了SEBS包裹的钙钛矿量子点薄膜稳定性优于PMMA.进一步对SEBS钙钛矿薄膜分别在空气、水等环境下的稳定性进行研究,相比钙钛矿量子点溶液4h衰退约18%,SEBS钙钛矿薄膜在空气中和水中衰退约18%延长至约55h和240h,说明SEBS包裹之后增强了钙钛矿量子点的稳定性,对钙钛矿量子点封装应用有着重要的意义.     

新型含咔唑聚芴类共轭聚电解质及其前驱体的合成与光电性能

采用Suzuki偶合反应成功地合成了一系列在主链上具有不同含量苯并噻二唑单元的聚咔唑和含胺基芴的衍生物:聚[3,6-(N-(2-乙基己基))咔唑-2,1,3-苯并噻二唑-9,9-双(N,N-二甲基胺丙基)芴](PCzN-BTDZ);通过对所得聚合物的季铵盐化后处理得到了其相应的聚电解质衍生物:聚[3,6-(N-(2-乙基己基))咔唑-2,1,3-苯并噻二唑-9,9-(双(3′-(N,N-二甲基)-N-乙基铵)丙基)芴]二溴(PCzNBr-BTDZ)。通过对它们的电致发光性能的研究,发现所有的聚合物用高功函数铝作阴极的器件具有和用钡/铝作阴极的器件相近的发光性能,说明这类聚合物具有良好的电子注入性能。不同比例的2,1,3-苯并噻二唑(BTDZ)的引入使聚合物中发生有效的能量转移,调节了聚合物的发光颜色;同时也提高了聚合物的器件性能。其中聚合物PCzN-BTDZ1在器件结构为ITO/PEDOT/PVK/Polymer/BaAl时的效率达0.99%,高于PCzN在相同器件结构时的效率(0.14%)。     

聚甲基丙烯酸甲酯和聚碳酸酯各向异性光学性质理论研究

作为重要的光学薄膜材料,聚甲基丙烯酸甲酯(PMMA)和聚碳酸酯(PC)在诸多工业领域已得到广泛应用.本文利用密度泛函理论结合分子动力学方法深入系统地研究了这两种聚合物的各向异性光学性质,并对比分析了不同分子链长度和微观结构对其各向异性光学性质的影响.计算结果表明PMMA和PC都具有较高的本征双折射率,且分子链长度对本征折射率的影响显著.在可见光范围内,单体单元PMMA本征双折射率在10%以上,而三单元结构本征折射率则不到4%.对于体相结构多聚体,从立方结构拉伸到厚度仅有6?的过程中,PC不同方向折射率最大差异高达6%,而同样情况下PMMA不同方向折射率差异仅有1.3%.此项研究有助于理解PMMA和PC聚合物各向异性光学特征产生的原因和影响因素,从而进一步指导和促进其在更多领域的发展与应用.     

采用密度泛函理论与分子动力学对聚甲基丙烯酸甲酯双折射性的理论计算

双折射性是各种光学材料的重要性能之一,具有高双折射率的光学材料在诸多研究及工业领域的应用越来越广泛.然而,作为常用的光学薄膜及光波导材料之一的聚合物材料的双折射性通常却很弱,只能通过实验对其双折射率进行大致的表征,缺乏对其双折射率的系统性理论计算,从而限制了提高聚合物双折射性的研究.本文建立了从聚合物的单体分子结构到多分子链的系统性的双折射率理论计算方法,并借助此方法研究了导致聚合物弱双折射性的限制因素.以聚甲基丙烯酸甲酯(PMMA)为研究对象,运用密度泛函理论研究了其本征双折射率,这里的本征双折射率是指分子链完全取向时其单体单元的双折射率.计算结果表明其本征双折射率高达0.0738左右,并且通过计算给出了PMMA单体单元的平均双折射率色散曲线.采用分子动力学方法研究了该聚合物(包含20个分子链)的材料双折射率.理论计算结果表明,尽管该聚合物具有较大的本征双折射率,但是由于聚合物中分子链取向度极低,聚合物材料最终表现出来的双折射率只有0.00052.本文建立的研究方法及研究结果为研究增强聚合物材料双折射性提供了理论依据.     

不同制备条件对聚偏氟乙烯纳米线生长的影响

为提高铁电聚合物聚偏氟乙烯(PVDF)的压电性能,利用纳米限域效应,采用模板直接浸润法,将多孔氧化铝(AAO)模板在不同浓度的PVDF的DMF溶液中自然浸润,并添加聚乙烯吡咯烷酮(PVP)作为表面修饰剂,制备了一维材料PVDF纳米线。分别研究了浸润温度、溶液浓度及表面修饰剂等因素对PVDF纳米线生长过程的影响。通过FTIR、SEM、XRD等对样品的形貌结构及性能进行了表征,进一步讨论了AAO模板中PVDF纳米线的生长机制。结果表明:模板法生长的PVDF纳米线形貌主要受溶液浓度的影响,并且当浓度为0.10 g/m L时形貌较优,其平均长度为50μm,平均直径为180 nm,与AAO模板孔径尺寸相当;表面修饰剂PVP可在一定程度上防止纳米线团聚并且优化其尺寸均一性;AAO模板中生长的PVDF纳米线由于纳米限域效应优先向β晶相结晶,并且在生长过程中PVDF并未参与任何化学反应。     

SiO2固态电解质中的质子特性对氧化物双电层薄膜晶体管性能的影响

本文采用等离子体增强化学气相沉积技术(PECVD)在室温条件下制备了具有双电层效应的二氧化硅(SiO₂) 固体电解质薄膜, 并以此SiO₂薄膜作为栅介质制备了氧化铟锌(IZO)双电层薄膜晶体管. 本文系统地研究了SiO₂固体电解质中的质子特性对双电层薄膜晶体管性能的影响, 研究结果表明, 经过纯水浸泡的SiO₂固体电解质薄膜可以诱导出较多的可迁移质子, 因此表现出较大的双电层电容. 由于SiO₂固体电解质薄膜具有质子迁移特性, 晶体管的转移特性曲线呈现出逆时针方向的洄滞现象, 并且这一洄滞效应随着栅极电压扫描速率的增加而增大. 进一步对薄膜晶体管的偏压稳定性进行测试, 发现晶体管的阈值电压的变化遵循了拉升指数函数(stretched exponential function)关系.     

Effect of PMMA on crystallization behavior and hydrophilicity of poly(vinylidene fluoride)/poly(methyl methacrylate) blend prepared in semi-dilute solutions

Films of poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend were derived from a special procedure of casting semi-dilute solutions. Hydrophilic character and crystallization of PVDF were optimized by variation of PMMA concentration in PVDF/PMMA blends. It was found that a PVDF/PMMA blend containing 70 wt% PMMA has a good performance for the potential application of hydrophilic membranes via thermally induced phase separation. The films presented β crystalline phase regardless of PMMA content existed in the blends. Thermal analysis of the blends showed a promotion of crystallization of PVDF with small addition of PMMA which induced larger lamellar thickness of PVDF, leading to the largest spherulitic crystal of PVDF (10 wt% PMMA) is about 8 μm. SEM micrographs illustrated no phase separation occurred in blends, due to the high compatibility between PVDF and PMMA.     

β-Phase of poly(vinylidene fluoride) formation in poly(vinylidene fluoride)/poly(methyl methacrylate) blend from solutions

The effect of single and mixed solvent on the crystallization behavior of the PVDF/PMMA blend from solutions was investigated. The films cast from the good solvent N,N-dimethylformamide (DMF) dominantly yielded the β-phase crystal with the highest crystallinity of PVDF. Those deposited from the methyl ethyl ketone (MEK) and tetrahydrofuran (THF) exhibited a mixture of α- and some extra β-phase crystals and presented the low crystallinity of PVDF. The crystallization behavior and morphology of the films cast from the mixed solvent (THF/DMF) revealed an enormous dependence on the DMF content. The increased DMF content in the mixed solvent enhanced the interactions between polymers and solvents, and favored the β-crystal of PVDF formation but hindered the α-phase of PVDF formation. Thus, the total crystallinity of PVDF in the blend film was decreased with the DMF content increasing, because of the decreased α-phase of PVDF. In addition, the morphological feature revealed that the voids between the PVDF spherulites were eliminated remarkably by blending with PMMA. The average size of the connected spherulite on top surface of the film can grow into larger as DMF content increased.     

Crystallizaion and surface morphology of poly(vinylidene fluoride)/poly(methylmethacrylate) films by solution casting on different substrates

The dependence of surface structure of the poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA) films by solution casting on properties of seven substrates was investigated by wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR), scanning electron microscope (SEM) and differential scanning calorimetry (DSC). It was revealed that the polyblend films obtained by casting onto each substrate contained exclusively β phase PVDF. Higher crystallinity of the film was obtained by casting onto ceramic, polytetrafluoroethylene (PTFE), copper (Cu), stainless steel and glass substrates than that by casting onto aluminium (Al) and polypropylene (PP) substrates, depending on the degree of close lattice matching. The surface crystalline structure of PVDF was strongly affected by the wettability of substrate. The largest size of PVDF spherulitic crystal structure with about 6 μm presented in the casting film grown at the air/solution interface on glass substrate, while the smallest spherulite size with about 3 μm was generated by casting onto PTFE, stainless steel and PP substrates. It implied that the higher surface tension the substrate had, the larger PVDF spherulite grew at the air/solution interface.     

Preparation of Poly(vinylidene fluoride)/Poly(methyl methacrylate) Blend Microporous Membranes via the Thermally Induced Phase Separation Process

The thermally induced phase separation (TIPS) process was employed to prepare poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blend microporous membranes. The effect of PMMA content on the dynamic crystallization temperature of the PVDF/PMMA/sulfolane system was analyzed. The effects of PMMA weight fraction and cooling rate on the cross-sectional morphology, crystallinity, crystal structure, thermal stability, and porous structure of the resulting membranes were investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and a mercury porosimeter, respectively. The mechanical properties of the membranes were evaluated by tensile tests. It was found that solid–liquid phase separation occurred in the PVDF/PMMA/sulfolane system. Scanning electron microscopy revealed that either increasing PMMA weight fraction or decreasing cooling rate will lead to a macroscopical phase separation between PVDF and PMMA. PMMA weight fraction and cooling rate had some influence on the crystallinity, porous structure, and mechanical properties, but no influence on the polymer crystal structure of the membranes. PMMA weight fraction influenced thermal stability of the final membranes but cooling rate did not.     

Nonisothermal Crystallization Kinetics of Poly(Vinylidene Fluoride) in a Poly(Vinylidene Fluoride)/Poly(Methyl Methacrylate)/Dipropylene Glycol Dibenzoate System via Thermally Induced Phase Separation

The nonisothermal crystallization kinetics of poly(vinylidene fluoride) (PVDF) in PVDF/polymethyl methacrylate (PMMA)/dipropylene glycol dibenzoate (DPGDB) blends, where DPGDB served as a diluent, via solid–liquid (S-L) phase separation during a thermally induced phase separation process was investigated through differential scanning calorimetry (DSC) measurements. It was found that the Ozawa model could only describe the nonisothermal crystallization behavior of PVDF/PMMA/DPGDB system to some extent. The influence of the cooling rate and PMMA/PVDF weight ratio in the PVDF/PMMA/DPGDB system on the crystallization mechanism was also examined based on the Avrami–Jeziorny method and Mo method. Primary crystallization and secondary crystallization were observed in the Avrami–Jeziorny analysis. The analysis by the Avrami–Jeziorny and Mo models indicated that the increase of PMMA/PVDF weight ratio decreased the crystallization rate during the primary crystallization stage. The results showed that the Mo method could well explain the kinetics of the primary PVDF crystallization. The Avrami–Jeziorny method, however, could not well describe the nonisothermal crystallization process of PVDF in the primary crystallization stage. The activation energy, determined by the Kissinger method, was not suitable to reflect the PVDF crystallization process in the PVDF/PMMA/DPGDB system.     

Effect of amphiphilic hyperbranched-star polymer on the structure and properties of PVDF based porous polymer electrolytes

An amphiphilic hyperbranched-star polymer (HPE-g-MPEG) was synthesized by grafting methoxy poly(ethylene glycol) to the end of the hyperbranched polyester (HPE) molecule using terephthaloyl chloride (TPC) as the coupling agent. The synthesized amphiphilic hyperbranched-star polymer was blended with poly(vinylidene fluoride) (PVDF) to fabricate porous membranes via typical phase inversion process, and then the membranes were filled and swollen by a liquid electrolyte solution to form polymer electrolytes. The influences of HPE-g-MPEG on the morphology, crystallinity, liquid electrolyte uptake, mechanical properties of the porous membranes and the electrochemical properties of the activated membranes were investigated. It was found that the addition of HPE-g-MPEG resulted in a significant increase in porosity and a considerable reduction in crystallinity of the blend membranes, which favored the liquid electrolyte uptake and, consequently, led to a remarkable increase in ion conductivity at ambient temperature. The maximum ion conductivity observed in this study was 1.76 × 10^? 3 S/cm at 20 °C for the blend membrane with a HPE-g-MPEG/PVDF ratio of 3/10 (w/w).     

Preparation and characterizations of PMMA-PVDF based polymer composite electrolyte materials for dye sensitized solar cell

Blend polymer composite gel electrolytesare prepared using thepoly vinyledene fluoride (PVDF), polymethyl methacrylate (PMMA) with alumina (Al₂O₃) in variance of alkali metal iodide saltsystem. The alumina doped blend polymer electrolytes characterized by the XRD diffraction and FT-IR spectra. This is supportive to the conformation of the crystallinity behaviour and the composite formation.The high-resolution scanning electron microscopy (HR-SEM) have used to find the composite electrolyte membrane porous size (10 μm) and it has support to understand the morphological structure of the membrane. To analyze the ionic conductivity of the potassium iodide based composite polymer electrolyte by the impedance measurements, which is 4.62 × 10⁻³ Scm⁻¹ at room temperature. Finally, different alkali metal iodide based dye-sensitized solar cells (DSSCs) fabricated and monitored an energy conversion efficiency.     

Photoactivated surface grafting from PVDF surfaces

Economic and easy methods to tune surface properties of polymers as Poly(vinylidene fluoride) (PVDF) without altering bulk properties are of major interest for different applications as biotechnological devices, medical implant device… UV irradiation appears as one of the simplest, easy and safe method to modify surface properties. In the case of self-initiated grafting, it is generally assumed that the pre-treatment of the PVDF surface with UV irradiation can yield alkyl and per-oxy radicals originating from breaking bonds and capable of initiating the subsequent surface grafting polymerizations. Surprisingly, the present work shows that it is possible to obtain polymer grafting using low energetic UV-A irradiation (3.1-3.9 eV) without breaking PVDF bonds. An EPR study has been performed in order to investigate the nature of involved species. The ability of the activated PVDF surface to graft different kinds of hydrophilic monomers using the initiated surface polymerization method has been tested and discussed on the basis of ATR FT-IR, XPS and NMR HRMAS results.     

Morphology,Crystallization and Formation Mechanism of Poly(Vinylidene Fluoride) Membranes Prepared with Immersion Precipitation: Effect of Maturation Time

Poly(vinylidene fluoride) (PVDF) membranes were prepared by the immersion precipitation method. Effects of the maturation time of dopes on the morphology and crystallization of the prepared membranes were investigated. The analysis showed that the maturation time played an important role in determining the morphology of the prepared membranes. For the dope prepared in the initial day, liquid–liquid demixing preceded solid–liquid demixing in the process of the membrane formation. The morphology of the cross section of the prepared membrane (M1) was finger-like structures with a sponge substrate beneath the porous skin. During the maturation, the dopes underwent a microscopic phase separation and the PVDF crystallized, which resulted in the existence of micro-liquid phases and micro-solid phase crystalline areas in the dopes. In the process of the membrane formation, liquid–liquid demixing took place by nucleation and growth of droplets of the polymer rich phase in the micro-liquid phase. The micro-solid phase crystallites were connected together by the polymer chains, and formed a three-dimensional network gelation morphology. The crystal structure of M1 was mainly β crystals. With increasing maturation time of the dopes, the proportion of β decreased crystals, but that of α crystals increased for the prepared membranes.     

Influence of pyrazole on the photovoltaic performance of dye-sensitized solar cell with polyvinylidene fluoride polymer electrolytes

We investigate the influence of the pyrazole content on the polyvinylidene fluoride (PVDF)/KI/I₂ electrolytes for dye-sensitized solar cells (DSSCs). The solid polymer electrolyte films consisting of different weight percentage ratios (0 20, 30, 40, and 50 %) of pyrazole doped with PVDF/KI/I₂ have been prepared by solution casting technique using N,N-dimethyl formamide (DMF) as a solvent. The as-prepared polymer electrolyte films were characterized by various techniques such as Fourier transform infrared spectroscopy (FT-IR spectroscopy), differential scanning calorimetry (DSC), X-ray diffractometer (XRD), alternate current (AC)-impedance analysis, and scanning electron microscopy (SEM). The 40 wt% pyrazole-PVDF/KI/I₂ electrolyte exhibited the highest ionic conductivity value of 9.52?×?10^?5 Scm^?1 at room temperature. This may be due to the lower crystallinity of PVDF and higher ionic mobility of iodide ions in the electrolyte. The DSSC fabricated using this highest ion conducting electrolyte showed an enhanced power conversion efficiency of 3.30 % under an illumination of 60 mW/cm² than that of pure PVDF/KI/I₂ electrolyte (1.42 %).