拉伸速率对PVDF薄膜介电压电性能的影响

通过单轴拉伸工艺制备了PVDF压电薄膜,运用X射线衍射和FTIR分析技术分析了不同拉伸速率下薄膜的微观结构;并探讨了极化电场对薄膜压电介电性能的影响.结果表明PVDF经单轴拉伸后,体系中出现了压电性能很强的β相和γ相,而且拉伸速率越高,体系出现的β相和γ相越多.随着极化电场的升高,PVDF压电薄膜的压电应变系数升高,介电常数升高,介电损耗降低.     

热拉伸温度对聚偏氟乙烯微孔膜结构与性能的影响

采用熔体挤出拉伸法以高、低分子量混合聚偏氟乙烯(PVDF)为原料制备微孔膜,研究了不同热拉伸温度对PVDF微孔膜表面形貌及结晶行为的影响,通过扫描电子显微镜、红外光谱仪、X射线衍射仪和差示扫描量热仪等测试手段分别对微孔膜的形态、结构、晶型进行表征.结果表明,热拉伸温度对PVDF微孔膜的成孔形貌、孔隙率、结晶度及β相含量均有影响.热拉伸温度为80℃时,微孔膜结晶度为58.86％,β相的相对含量最高达到42.50％,此时微孔膜的力学性能最佳;而当热拉伸温度为120℃时,PVDF微孔膜的成孔分布更加均匀,其孔隙率可达到最大值31.51％.     

不同溶剂配比及后处理温度对电纺PVDF/PEI复合纤维薄膜β相含量的影响

β相聚偏氟乙烯(PVDF)因其具有良好的压电、热电性能而受到广泛的关注。按质量比聚偏氟乙烯(PVDF)/聚醚酰亚胺(PEI)为8/2的混合聚合物溶解在N,N-二甲基甲酰胺(DMF)、四氢呋喃(THF)不同比例的混合溶剂中。利用静电纺丝技术制备PVDF/PEI复合纤维薄膜。通过SEM、XRD、FT-IR测试分析静电纺丝过程中不同溶剂质量比以及不同后处理温度对制备的PVDF/PEI复合纤维膜的结晶度、结晶部分中β相含量和复合纤维薄膜铁电性能的影响,得到了制备高β相含量PVDF的最优化的溶剂配比和后处理温度。     

PVDF铁电聚合物薄膜的溶液法制备

采用溶液流延法制备了β相聚偏二氟乙烯(PVDF)铁电聚合物薄膜,研究了不同热处理条件和不同溶剂对薄膜晶相结构形成的影响.利用X射线衍射仪、傅立叶红外光谱仪(FTIR)对晶形结构进行了分析.结果表明,在合适的温度条件下,基片的热诱导作用有利于β晶相形成,而在较高温度下主要形成γ晶相,较低的温度将会抑制PVDF结晶;溶剂的溶度性能对薄膜的结晶能力和晶型的形成有很大影响,采用对PVDF溶解能力较强的溶剂DMSO所制备的薄膜中晶区内β晶型的含量高但其结晶能力差,而采用溶解能力较弱的DMAc溶剂虽然提高了薄膜的结晶度,却降低了β晶型的含量.     

退火温度对PVDF薄膜结构的影响及其性能研究

通过拉伸工艺,在不同的退火温度下,制备了PVDF薄膜,用XRD分析了退火温度对拉伸PVDF薄膜β相含量的影响.实验结果表明,退火温度为120℃时,β相的含量达到最大值,薄膜呈现明显的铁电性,矫顽场接近1.0mV/cm,电位移D为5μC/cm2.在25℃时,薄膜的热释电系数p为0.3×10-8C/cm2·K.     

拉伸速率对β-iPP薄膜微观结构和力学性能的影响

通过熔体挤出-拉伸法制备了一系列稀土类β成核剂改性等规聚丙烯(iPP)薄膜。考察了拉伸速率对β-iPP薄膜微观结构和力学性能的影响。结果表明,所有β-iPP薄膜中α晶和β晶均发生支化现象,并且β晶支化随着拉伸速率的增加而受到抑制,而α晶支化没有发生明显变化;β-iPP薄膜的分子链和片晶的取向度随着拉伸速率增加而增大,而β晶含量及其结晶度呈现相反的趋势。另外,拉伸测试结果表明,当拉伸速率为30cm/min,β-iPP薄膜的拉伸强度和韧性达到最大值。     

聚偏氟乙烯压电薄膜的制备及结构

采用溶液浸渍提拉法制备了β型PVDF压电聚合物薄膜,采用X衍射、扫描电镜等手段测定了PVDF薄膜的物相结构,结晶形态及薄膜厚度等.结果表明,基板的诱导作用使PVDF在较低温度下结晶形成极性的正交β相晶,在较高温度下结晶形成非极性的单斜相α晶.在低温下得到的PVDF薄膜中β晶呈典型的球晶结构,晶粒粒径随着膜厚的增加而增大,α晶体颗粒的堆积疏松,薄膜致密性差;在较高温度下形成的α晶相,以二维生长为主,晶粒大小随着膜厚的增加基本上保持不变,晶颗粒间接触紧密,薄膜致密性好.     

固相剪切碾磨对聚偏氟乙烯结构和介电性能的影响

利用固相剪切碾磨技术(S~3M)制备了高β晶含量的聚偏氟乙烯(PVDF)微米级粉体,研究了PVDF粉体的结构形态、粒径及粒径分布,碾磨遍数对粉体结晶结构和介电性能的影响。结果表明,固相力化学反应器强大的挤压和剪切作用可使PVDF中α晶转变为晶,从而有效提高PVDF粉体中β晶相对含量;随碾磨遍数增加,PVDF粉体β晶含量逐渐提高,未碾磨PVDF中的β晶相对含量为37%,碾磨15遍后β晶相对含量达90%以上;同时,介电常数则由1.20增加至10.77,提高约1个数量级。固相剪切碾磨技术为高介电性能材料的制备提供了新途径。     

PVDF薄膜的低维化制备和结构研究

采用真空热蒸发技术在单晶硅基底上沉积PVDF薄膜.通过分析阻蒸温度对薄膜沉积速率和真空室气压变化的影响研究了PVDF镀膜过程.同时利用傅立叶变换衰减全反射红外光谱(ATR-FTIR)、X射线衍射(XRD)和差热分析(DSC)对薄膜的晶型结构进行了表征分析,结果发现,真空热蒸发技术可制备具有高度取向性的α晶相PVDF薄膜,且薄膜中不舍C=C键.相比于PVDF树脂粉末,所得薄膜的结晶度明显增大而分子量显著减小,实现了PVDF薄膜的低维化制备.     

高性能自增强聚烯烃材料挤出及流场的研究

本研究工作在国内外首次把聚合物的熔体连续挤出自增强及熔体在收敛流道内的速度与延伸应变速率的分布规律联系起来进行研究。 采用可视化实验观测与理论分析相结合的方法,揭示了楔形收敛流道内与聚合物熔体挤出自增强紧密相关的流场参数(速度与延伸应变速率)的变化规律。接近收敛流道出口端的很窄范围内,熔体所受的延伸应变速率随流向而迅速增大,因而取向分子链最易于结晶。 在流场研究的基础上,采用普通挤出设备并通过控制挤出压力与熔体温度,成功地实现了熔体的连续挤出自增强,由2种HDPE与1种PP制备了厚度1.5mm、宽度20mm的自增强片材以及直径5mm的自增强棒材。经SEM观察、DSC分析、拉伸测试、摩擦测试、显微硬度测试与透光率测试,结果充分显示了本研究制备的自增强片材具有很高的综合性能,尤其是拉伸强度。40MPa机头压力下制备的自增强HDPE片材与PP片材的拉伸强度最高值分别达229.2MPa与288.11MPa(分别为相应普通试样的8.2与8.1倍),它们已超过被称为超高性能工程塑料的液晶聚合物的拉伸强度,比拉伸强度的最高值比高级合金钢的还要高。与普通片材相比,对40EPa机头压力下制备的自增强HDPE片材,沿其挤出方向的摩擦系数低30.7％、耐磨性能提高2.5倍、显微硬度提高1.2倍,其透光率提高达4.6倍。 本研究表     

聚偏氟乙烯电纺纤维膜的制备及其热释电性能研究

β晶相的聚偏氟乙烯(PVDF)由于具有强压电和热释电特性,被广泛应用在能量收集、红外探测等领域。采用静电纺丝技术制备PVDF纤维,通过SEM以及XRD表征,研究了溶剂组成、溶液浓度和纺丝液供给速度等纺丝参数对PVDF纤维膜形貌和β晶相含量的影响,制备出连续、均匀、直径约600nm的PVDF纤维。另外,测试了PVDF纤维膜对不同调制频率的3.4μm波长红外光的热释电响应特性。     

Enhancement of β phase crystals formation with the use of nanofillers in PVDF films and fibres

Nanoclay and carbon nanotubes (CNT) have been in focus recently as means of enhancing β phase crystals formation in poly(vinylidene fluoride)(PVDF). Dominantly, the so-far work has been carried out on films/thin sheets filled with nanoclay. It has been found, mainly from combined XRD and DSC data, that nanoclay influences the PVDF structure, and particularly the β phase crystals formation is enhanced. Results published by various groups are in fairly good agreement. There are no results for nanoclay filled melt-spun PVDF fibres.The influence of CNT on PVDF structure has been less studied. XRD data indicating an enhancing role of multi-wall carbon nanotubes (MWNT) on β phase crystals formation in solution compounded PVDF films are available. Published results for MWNT/PVDF films are not in good agreement. The only study into single-wall carbon nanotube (SWNT)/PVDF has been made on electrospun nanofibres.We explore above findings towards melt-spun nanofilled PVDF fibres. We present new results obtained by us for melt-spun PVDF fibres containing non-functionalized and amino-functionalized double-wall carbon nanotubes (DWNT). The key finding is that amino-DWNT can influence the β to α polymorphic balance.     

Effect of CoCl<Subscript>2</Subscript>–BaCl<Subscript>2</Subscript> fillers on morphology,dielectric constant and conductivity of PVDF composite for pressure sensing application

This present study focuses on the effect of addition of CoCl₂–BaCl₂ fillers on the β phase formation and dielectric constant in the PVDF composite films. The pristine and filler based PVDF films were prepared using solution casting technique. XRD analysis were carried out to investigate the crystalline structure in the prepared composite films. The surface morphology of the films were observed using SEM indicating the formation of agglormated structures. The UV–Vis absorption spectrum was obtained to investigate the effect of filler concentration on the optical band gap. The decrease in optical band gap with increase in filler concentration was confirmed from Tauc plot. The incorporation of filler significantly improved the ac conductivity. The dielectric study reveals the increase in value of dielectric constant from 10.8 to 42.3 as the filler content increased from 0 to 12 wt%. A pressure measurement set up was developed and voltage output was measured from the PVDF thin film sensor for variation in applied pressure.     

Enhanced electrical properties of multiwalled carbon nanotube/poly(vinylidenefluoride) films through a rolling process

Poly(vinylidene fluoride) (PVDF) films containing multiwalled carbon nanotubes (MWCNTs) were prepared by solution casting method, followed by a rolling process. With the presence of MWCNTs (up to 0.3 wt%), the influence of rolling process on the crystal structure and the electrical properties of PVDF was studied. It is shown that rolling can induce phase transition as well as increase in the crystallinity of PVDF, leading to enhancement of ferroelectric and dielectric properties. In addition, MWCNTs may promote the phase transition of PVDF, while impeding the increase of crystallinity during the rolling process. With a higher breakdown field and a lower coercive electric field in comparison with the original films, the rolled films can be efficiently poled to obtain good piezoelectricity. Moreover, with the presence of MWCNTs, electric field-induced changes in crystallinity can be obviously observed in the poled MWCNTs/PVDF films. With the highest crystallinity of β-phase, the rolled films containing 0.075 wt% MWCNTs possess the highest piezoelectric coefficient d₃₃ of ~33 pC/N while that of pure PVDF films is only ~22 pC/N.     

Ni/PVDF复合薄膜电性能的拉伸改性

为了进一步研究聚合物基复合材料的拉伸效应,采用简单的物理混合法制备了Ni/PVDF复合薄膜并在120℃下进行拉伸改性研究。结果表明：镍含量远低于渗流阈值的样品,通过拉伸实现了与渗流效应类似的介电常数剧增的拉伸渗流效应;在伸长倍数为2.3时介电常数急剧增大,最大增幅17倍(12→220),同时电导率也增大了4～5个数量级,薄膜有绝缘体向导体转变的趋势。介电常数随拉伸倍数增加而大幅增加,是因为复合薄膜中的镍颗粒在外力拉伸作用下,其分布、微观结构逐步发生变化,以致形成了杆状镍颗粒群和微平行电容器结构等导电网络,发生拉伸渗流效应;同时,电导率的大幅增加也符合渗流理论的特征。     

Development and mechanical characterization of solvent-cast polymeric films as potential drug delivery systems to mucosal surfaces

Solvent-cast films from three polymers, carboxymethylcellulose (CMC), sodium alginate (SA), and xanthan gum, were prepared by drying the polymeric gels in air. Three methods, (a) passive hydration, (b) vortex hydration with heating, and (c) cold hydration, were investigated to determine the most effective means of preparing gels for each of the three polymers. Different drying conditions [relative humidity – RH (6–52%) and temperature (3–45°C)] were investigated to determine the effect of drying rate on the films prepared by drying the polymeric gels. The tensile properties of the CMC films were determined by stretching dumbbell-shaped films to breaking point, using a Texture Analyser. Glycerol was used as a plasticizer, and its effects on the drying rate, physical appearance, and tensile properties of the resulting films were investigated. Vortex hydration with heating was the method of choice for preparing gels of SA and CMC, and cold hydration for xanthan gels. Drying rates increased with low glycerol content, high temperature, and low relative humidity. The residual water content of the films increased with increasing glycerol content and high relative humidity and decreased at higher temperatures. Generally, temperature affected the drying rate to a greater extent than relative humidity. Glycerol significantly affected the toughness (increased) and rigidity (decreased) of CMC films. CMC films prepared at 45°C and 6% RH produced suitable films at the fastest rate while films containing equal quantities of glycerol and CMC possessed an ideal balance between flexibility and rigidity.     

聚偏氟乙烯/碳纳米管纳米复合材料的制备和表征

采用超声波分散法制备了聚偏氟乙烯(PVDF)/多壁碳纳米管(MWCNT)复合材料。利用扫描电子显微镜、差示扫描量热法和傅立叶变换红外光谱等方法研究了复合材料的形态,考察了MWCNT用量对复合材料结晶行为和力学性能的影响。结果表明,通过超声处理,PVDF和MWCNTs之间产生了相互作用,复合体以球状的形式存在。MWCNTs的引入导致具有压电性的β相形成和屈服强度的提高。根据实验结果,对PVDF/MWCNT复合球体和β相的形成机理提出了可能的解释。     

Phase transition in poly(vinylidene fluoride) investigated with micro-Raman spectroscopy

The phase transition from the non-polar alpha-phase to the polar beta-phase of poly(vinylidene fluoride) (PVDF) has been investigated using micro-Raman spectroscopy, which is advantageous because it is a nondestructive technique. Films of alpha-PVDF were subjected to stretching under controlled rates at 80 degrees C, while the transition to beta-PVDF was monitored by the decrease in the Raman band at 794 cm(-1) characteristic of the alpha-phase, along with the concomitant increase in the 839 cm(-1) band characteristic of the beta-phase. The alpha-->beta transition in our PVDF samples could be achieved even for the sample stretched to twice (2x-stretched) the initial length and it did not depend on the stretching rate in the range between 2.0 and 7.0 mm/min. These conclusions were corroborated by differential scanning calorimetry (DSC) and X-ray diffraction experiments for PVDF samples processed under the same conditions as in the Raman scattering measurements. Poling with negative corona discharge was found to affect the alpha-PVDF morphology, improving the Raman bands related to this crystalline phase. This effect is minimized for films stretched to higher ratios. Significantly, corona-induced effects could not be observed with the other experimental techniques, i.e., X-ray diffraction and infrared spectroscopy.     

Dielectric and magnetic properties of ferrite/poly(vinylidene fluoride) nanocomposites

Particulate composite films of poly(vinylidene fluoride) and CoFe₂O₄ and NiFe₂O₄ were prepared by solvent casting and melt processing. The well-dispersed ferrite nanoparticles nucleate the piezoelectric β-phase of the polymer, but the different ferrites nucleate the whole polymer crystalline phase at different filler concentrations. The macroscopic magnetic and dielectric response of the composites demonstrates a strong dependence on the volume fraction of ferrite nanoparticles, with both magnetization and dielectric constant increasing for increasing filler content. The β-relaxation in the composite samples is similar to the one observed for β-PVDF obtained by stretching. A superparamagnetic behavior was observed for NiFe₂O₄/PVDF composites, whereas CoFe₂O₄/PVDF samples developed a hysteresis cycle with coercivity of 0.3 T.     

聚偏氟乙烯基复合材料的制备及介电性能

为有效改善聚合物基复合材料的介电性能,兼顾高介电常数和低填料量同时并存,采用以聚偏氟乙烯(PVDF)为基体树脂,钛酸钡(BT)和石墨烯(GNP)分别为介电填料和导电填料,在BT-GNP/PVDF复合体系内部构建微电容器结构。采用溶液法和热压法制备GNP/PVDF薄膜和BT-GNP/PVDF复合薄膜。结果表明,BT和GNP填料在BT-GNP/PVDF复合薄膜中能够均匀分散,在薄膜内能形成明显的微电容器结构。陶瓷填料BT的引入,使微电容器结构更有利于提高BT-GNP/PVDF复合薄膜的介电常数。BT含量大于50wt%的BT-GNP/PVDF复合薄膜介电常数均不低于GNP/PVDF薄膜。BT含量为50wt%的BT-GNP/PVDF复合薄膜的介电常数高于BT含量分别为35wt%、60wt%和70wt%的BT-GNP/PVDF复合薄膜,最大值约为43,相当于GNP含量为0.8wt%的GNP/PVDF薄膜的1.5倍;BT含量为50wt%的BT-GNP/PVDF复合薄膜损耗角正切均小于其他体系薄膜,最大不超过0.09,最小约为0.02。BT-GNP/PVDF复合薄膜的电导率变化趋势基本一致,没有明显差异。