Sound absorption behavior of electrospun polyacrylonitrile nanofibrous membranes

The acoustical damping property of electrospun polyacrylonitrile(PAN) nanofibrous membranes with different thicknesses and porosities was investigated.The sound absorption coefficients were measured using the impedance tube instrument based on ISO 10534-2:1998(E).Results indicate that the first resonance absorption frequency of nanofibrous membranes shifts to the lower frequency with the increase of the back cavity or the thickness of membranes.Moreover,the sound absorption performance of the perforated panel can be greatly improved by combination with a thin layer of PAN nanofibrous membrane.Traditional acoustical damping materials(foam,fiber) coated with nanofibrous membranes have better acoustical performance in the low and medium frequency range than that of acoustical materials alone.All of the results demonstrate the PAN nanofibrous membrane is a suitable candidate for noise reduction.     

全固态聚苯胺-二氧化钛电致变色器件的制备

以聚苯胺(PANI)为电致变色材料,分别制备了对称结构(SSECD,ITO‖PANI‖解质‖PANI‖lTO)和非对称结构(ASECD,ITO‖PANI‖电解质‖TiO<,2>‖ITO)的全固态电致变色器件.TO<,2>薄膜的制备采用提拉法.经500℃处理后得到锐钛矿结构,所得薄膜由粒径10-20 nm的TiO<,2>...     

Bragg grating chemical sensor with hydrogel as sensitive element

A novel fiber Bragg grating (FBG) based chemical sensor using hydrogel, a swellable polymer, as sensitive element is demonstrated. The sensing mechanism relies on the shift of Bragg wavelength due to the stress resulted from volume change of sensitive swellable hydrogel responding to the change of external environment. A polyacrylamide hydrogel fiber grating chemical sensor is made, and the experiments on its sensitivity to the salinity are performed. The sensitivity is low due to the less stress from the shrinking or swelling of hdrogels. Reducing the cross diameter of the grating through etching with hydrofluoric acid can greatly improve the sensitivity of the sensor.     

2D SAXS/WAXD analysis of pan carbon fiber microstructure in organic/inorganic transformation

Structure of PAN fibers during pre-oxidation and carbonization was studied using two dimensional small angle X-ray scattering/wide angle X-ray diffraction(2D SAXS/WAXD).The SAXS results show that during pre-oxidation between 180 ℃ and 275 ℃,the volume content of microvoids increases with the temperature increasing,which may be one of reasons for the decrease of tensile strength of pre-oxidized fibers.253 ℃ was the critical transition temperature,the length,diameter,aspect ratio and orientation distribution of microvoids increased with temperature before this temperature and decreased after this temperature.After the high temperature carbonization,lots of spindly microvoids formed.WAXD patterns demonstrate that the crystallite size of PAN fibers first increased before 230 ℃ and then decreased with the increase of temperature during the pre-oxidation.The diffraction peak of PAN fibers at 2θ≈ 17° almost disappeared at the end of preoxidation while the diffraction peak of aromatic structure at 2θ≈ 25° appeared at 253 ℃.During carbonization,the peak intensity at 2θ≈ 25° increased apparently due to the formation of graphite structure.The results obtained give a deep understanding of the microstructure development in the PAN fibers during pre-oxidation and carbonization,which is important for the preparation of high performance carbon fibers.     

溶液预凝胶化对再生纤维素水凝胶膜性能的影响

研究了溶液预凝胶化对纤维素/NaOH/尿素水溶液体系以浸没沉淀相转化法制备的再生纤维素水凝胶膜的影响.通过静态拉伸、扫描电子显微镜研究了预凝胶化温度、凝固浴温度、凝固浴组成对再生纤维素水凝胶膜结构和性能的影响.结果表明,与常规的浸没沉淀相转化法相比,使溶液预凝胶化可以提高所制备的水凝胶膜的机械性能.经60℃预凝胶30 min后制备的水凝胶膜,拉伸强度比未经预凝胶处理的水凝胶膜提高85%.凝固浴温度的升高和凝固浴中硫酸浓度的增大均会导致形成具有较大孔结构的纤维素水凝胶膜,机械性能也随之下降.     

高性能聚丙烯腈碳纤维中纳米级微孔分析表征研究

高性能碳纤维由于其优异的性能,在各行各业中具有广泛应用。为深入研究碳纤维内结构与其性能之间的相关性,本文应用小角X射线散射研究了一系列典型的聚丙烯腈碳纤维样品,分析了样品内微孔的尺寸及取向,讨论了强度和模量与微孔的相关性,研究结果表明:高性能碳纤维的力学强度和模量与碳纤维内微孔缺陷的长度和长径比有关,控制碳纤维内微孔缺陷的长度有望实现高强碳纤维的制备,控制牵伸倍率从而控制碳纤维内微孔的长径比有望实现高模碳纤维的制备。     

A Thermodynamic Analysis of the Validity of Wenzel and Cassie＇s Equations ＊

Wettable properties of a considered solid on its contact angle （CA） can be analyzed theoretically using the classical Wenzel and Cassie＇s equations. However, recent strong interest in superhydrophobic surfaces has demanded a re-examination of the applicability of the two equations. We report a thermodynamic analysis to determine the universality, in particular, the limitations of the two equations. Using some special surfaces, we demonstrate that the two equations are valid for micro-scale heterogeneous structures, however they are invalid for macro-scale heterogeneous surfaces. Furthermore, the present calculations suggest that fundamental thermodynamic analysis is the most powerful and reliable approach to determine the comprehensive wettability for various structurally patterned surfaces.     

RCA TA8694和TA8777微波功率晶体管的可靠性研究

1.0 引言本方案的目的在于检查、最佳化、提高和确定用铝作金属化可输出28瓦的 TA8694晶体管和用金作金属化及管芯载体封装的可输出40瓦的 RCAT A8777晶体管的失效前平均时间。为了提高失效前平均时间,使晶体管性能最佳化,仔细分析了器件失效模式和机理,随后并进行了校准测量。朝着使失效前平均时间达到10~0器件小时的最终目标而努力。2.0 方案的目的为了用有效而及时的方法达到此目的,方案工作分成二个独立的任务,下面称为第一阶段和第二阶段。     

测定含甲基丙烯酰氧端基大分子单体分子量的新方法

建立了用紫外分光光度法测定含甲基丙烯酰氧端基大分子单体数均分子量的新方法 .在本实验条件下 ,以 95%乙醇∶THF( 7∶3 )为溶剂 ,在最大吸收波长 2 1 3nm处对含甲基丙烯酰氧端基的聚四氢呋喃大分子单体进行定量分析 ,所得结果与端基滴定分析法所得结果最大相对误差小于± 5% ,用t检验法对两法测定结果差别进行显著性检验 ,两法所得结果差别无显著意义 .紫外分光光度法可成为一种表征含甲基丙烯酰氧端基大分子单体数均分子量的方便方法 .