静电纺丝参数对聚乙酸乙烯酯纤维形貌的影响

以N,N-二甲基甲酰胺(DMF)为溶剂,采用静电纺丝法制备了聚乙酸乙烯酯(PVAc)纤维.用场发射扫描电镜观察了PVAc纤维的形貌,研究了PVAc溶液质量分数、纺丝电压、收集距离等对纤维形貌及平均直径的影响.研究结果表明,PVAc溶液质量分数和纺丝电压对纤维的形貌有显著影响,随着PVAc溶液质量分数和纺丝电压的增大,纤维的平均直径增大;收集距离对纤维形貌的影响较小.尝试采用静电纺丝法制备了炭黑和PVAc的复合纤维,以增强纤维的导电性,成为导电碳纤维,但炭黑会显著降低PVAc的成纤性,因为它会吸附溶剂DMF,使溶剂在电纺过程中不易挥发,射流不能固化成纤维.     

溶液静电纺丝制备热塑性聚酰亚胺超细纤维无纺布

为实现热塑性聚酰亚胺(LPI)无纺布的宏量制备奠定基础,以N-N-二甲基乙酰胺(DMAc)为溶剂,采用静电纺丝技术成功制备了平均直径范围为0.36~1.47μm的LPI超细纤维,系统探讨了纺丝液浓度、流速以及纺丝电压等工艺条件对LPI纤维形貌和直径的影响。结果表明:随着浓度从22%(质量分数,下同)增加到30%,LPI纤维的平均直径显著增大,同时直径分布逐渐变宽,并且在纺丝溶液浓度较低时,有纺锤状纤维存在,随着溶液浓度上升,纺锤状纤维消失,随浓度继续上升,纤维开始产生粘连。纺丝电压的改变对纤维的形貌和平均直径变化不显著;随着流速增加,纤维平均直径随之增大,当流速大于1.5mL/h时,开始出现纤维粘连,大于1.8mL/h时,出现纺锤状纤维。通过优化工艺条件,在LPI浓度28%,电压15kV,流速1.2mL/h,温度30℃,接收距离25cm条件下,制备了平均直径为1.18μm的纤维。     

动态线性电极静电纺PVA纳米纤维的可纺性

为了解决传统针式静电纺针头易堵塞不易产业化的问题,采用铜丝动态线性电极静电纺丝技术对PVA纳米纤维的可纺性进行研究。利用扫描电子显微镜研究了PVA溶液浓度、电压和纺丝距离对PVA纤维形貌及直径分布的影响。结果表明:随PVA溶液浓度降低,溶液粘度和电导率减小,纤维直径及其分布变小。且随纺丝距离增大,纤维直径变细,纤维形貌变好。当PVA浓度为10%(质量分数),电压80 kV,距离30 cm时,可制备出形貌良好的纳米纤维,其直径为433 nm,产量高达 6.8 g/h ;当PVA浓度为5%(质量分数),电压80 kV,距离30 cm, 可纺最细纤维直径为96 nm。本研究可为未来PVA静电纺纳米纤维膜的规模化制备提供参考。     

熔体静电纺聚乳酸纤维膜的制备、表征及细胞毒性评价

调试熔体静电纺聚乳酸(PLA)过程中的电压场和温度场的参数,对不同条件下的纤维膜进行测试,研究电压场与温度场与纤维直径间的关系,并评价熔体静电纺PLA膜的细胞毒性。以聚乳酸(PLA)为原料,采用熔体静电纺丝方法,电压调整在20~26 k V范围,空间温度在10~70℃之间,分别进行熔体纺丝实验,将制得的纤维膜进行细胞毒性评价。熔体静电纺丝PLA纤维的平均直径随电压的升高逐渐增大,当空间温度为50℃时,所得纤维平均直径为最小。细胞活力测试证实熔体静电纺PLA膜无细胞毒性,具有良好的组织工程材料的应用前景。     

纳米碳纤维的制备及其表面结构分析

用电场纺丝方法制得了PAN原丝,经碳化制备纳米碳纤维;并用因子设计方法研究PAN原丝平均直径的影响因素;用扫描电镜(SEM)、扫描隧道显微镜(STM)研究了纳米碳纤维的表面形貌及结构.结果表明溶液的浓度是PAN原丝平均直径的主要影响因子,电压对原丝的平均直径没有明显的影响;用电场纺丝方法可以制得直径在80～500nm之间的纳米碳纤维;电场纺丝制得的纳米碳纤维表面有长度约为10nm左右,宽度约为5nm沿纤维方向取向的凹坑,该结构有利于进一步增加纤维的比表面积和吸附性能,该类纤维在复合材料领域有潜在的应用前景.     

静电纺再生丝素纳米纤维:纤维直径分布与力学性能

采用静电纺丝的方法研制了再生丝素纳米纤维(ERSF)膜,纤维直径为50～1000nm.将脱胶后的桑蚕丝溶解在摩尔比为1:2:8 的60℃CaCl2/CH3CH2OH/H2O三元体系中,将该溶液冷冻干燥后溶解在98%的甲酸中得到再生丝素溶液,对其进行静电纺丝.研究了不同纺丝条件下,静电纺再生丝素纤维的直径分布.研究发现:在一定的电压和喷丝头与接收屏的距离(C-D)下,7wt%是具有良好可纺性的临界浓度.纤维的直径随着溶液浓度的增加而增大,随着C-D的增加而减小,并且在C-D较大时可以获得较均匀的纤维.电压是另一个影响纤维直径的重要因素,当电压高于某一数值时,可以纺得细而均匀的纳米级再生丝素纤维.在9wt%,12cm C-D and 15KV 的纺丝条件下,80%的纤维直径在50～150nm之间.由于所纺得的再生丝素纤维膜在水中会产生收缩,因此用甲醇和丙酮对其进行处理.力学性能是影响纤维膜实际使用的重要性能,我们测定和分析了静电纺再生丝素纤维膜处理前后的力学性能.     

静电纺工艺参数对含银PA6纳米纤维直径的影响

为了研究静电纺工艺参数对含银PA6纳米纤维直径分布的影响,采用静电纺丝技术,在不同含银量、纺丝液质量分数、纺丝电压、接收距离(C-SD)、喷嘴直径条件下制备出含银PA6纳米纤维膜.利用扫描电镜(SEM)及相关软件分析纳米纤维直径分布及形态,在银溶胶质量分数0.2%～0.4%、纺丝液质量分数10%～16%、纺丝电压12～21kV、接收距离9～18cm、喷嘴直径0.5～1.2mm的实验范围内,纳米纤维的平均直径为70～90nm;纳米纤维直径随银溶胶质量分数的增加而减小,随纺丝液质量分数的增加而增大,随喷嘴直径的增大而增大;电压和接收距离对纳米纤维直径的影响较小.     

肌腱仿生用定向PLLA微纳米纤维的静电纺丝工艺参数研究

采用左旋聚乳酸(PLLA)为基材研究静电纺丝工艺过程对聚乳酸纤维形貌和性能的影响,主要包括环境湿度、纺丝溶液浓度、接收转速、收集距离、注射泵推注速度、附加电压等过程参数。结果表明,接收转速与纺丝液浓度分别是影响纤维定向排列程度和纤维直径的最主要因素,其次是接收距离、环境湿度、推注速度。当聚乳酸-氯仿溶液聚合物质量浓度为80 mg/mL、纺丝电压为25 kV、接收距离为20 cm、注射泵推注速度为0.3 μL/s以及接收转速为1500 r/min时,纤维取向性良好,平均直径为(0.94±0.21) μm,可达到模拟肌腱组织天然细胞外基质结构的要求。     

高压静电纺丝制备聚丁烯-1纤维的形貌及晶型转变

对聚丁烯-1的环己烷溶液进行高压静电纺丝制备出聚丁烯微纳米纤维,通过光学显微镜、扫描电镜、傅里叶变换红外光谱和X射线衍射等表征手段,考察了纺丝液浓度、纺丝电压、推进速率对纤维形貌的影响,并对纺丝过程及室温陈放的聚丁烯纤维的晶型转变进行了研究。结果表明,随着纺丝液浓度和推进速率的增大,可以得到尺寸均匀的纤维,直径也随之变大;纺丝电压增大,纤维直径减小,但纤维直径分布均匀性变差。初生聚丁烯-1纺丝纤维膜的晶型为I型和II型,随着溶剂的挥发和时间延长,晶型II逐渐转变为晶型I,溶液涂覆膜初生晶型为晶型III和晶型I'。     

静电纺丝法制备聚乳酸纳米纤维及其吸油性能

本文采用静电纺丝法制备了聚乳酸(PLA)纳米纤维毡片,并首次研究了PLA纳米纤维微观结构对材料吸油性能的影响机制。扫描电子显微镜(SEM)表征显示前驱体溶液浓度对PLA静电纺丝纳米纤维直径具有显著影响,较高的浓度导致纳米纤维直径变大,10wt.%的前驱体溶液浓度可获得直径为50~100nm的均匀纳米纤维。接触角测定发现优化后的PLA纳米纤维材料具有超疏水超亲油特性。系统研究了PLA静电纺丝纳米纤维毡片对柴油、润滑油和植物油的吸附性能,发现PLA静电纺丝纳米纤维对柴油、润滑油和植物油的最大吸油倍率分别达到37、116和51g/g。实验模拟发现所制备的PLA纳米纤维材料具有吸油倍率高,吸水率低和可生物降解等特点,可用于吸附水面溢油。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.