静电纺丝理论模型的研究进展

静电纺丝技术是制备纳米纤维最直接、最有效的方法之一,其生产过程简单经济从而成为世界研究的热点。但是由于静电纺丝过程的复杂性,导致其研究一直处于实验阶段。如何完善数学、力学等理论模型是静电纺丝研究的基础问题,对静电纺丝工艺参数和设备制造有着重要的意义。本文论述了国内外静电纺丝理论模型的研究现状和进展,重点介绍了静电纺丝射流理论模型的研究及需要解决的理论问题,展望了静电纺丝理论模型研究的发展前景。     

静电纺丝技术在新能源电池中应用的研究进展

简要介绍了五种新能源电池和静电纺丝技术,综述了静电纺丝技术用于锂电池的正负极材料和燃料电池电极材料的现状,以及应用静电纺丝技术制备电极隔膜材料。静电纺丝制备纳米纤维具有直径小、比表面积大、孔隙率高等特点,用于正负电极和隔膜材料将大大提高电池的比容量、充放电速率和充放电电流,从而提高电池的蓄电能力、循环性能、离子导电性、力学稳定性和化学稳定性。最后总结了静电纺丝技术产业化需要解决的问题,并展望了在新能源电池中的进一步应用。     

纤维素及其衍生物的高压静电纺丝

高压静电纺丝作为一种制备纳米纤维的先进技术,近年来受到普遍关注。而纤维素和纤维素衍生物由于其优越的性质已应用于各个领域。运用高压静电纺丝技术对纤维素及其衍生物进行研究,开拓了新的研究领域和发展方向。本文介绍了高压静电纺丝技术的研究背景和原理,总结了近几年研究者们在纤维素以及纤维素衍生物高压静电纺丝方面的工作进展,尤其对不同溶剂体系溶解纤维素用于静电纺丝的优缺点进行了比较,评述了这方面的前沿性探索研究,并对未来的发展进行了展望。     

取向静电纺丝纳米纤维的制备及应用研究进展

简单描述了静电纺丝的基本装置、原理;为制得高性能的取向纳米纤维,对静电纺丝中出现的不稳定性进行了研究,介绍了三种不稳定状况,并分析了其产生原因.列举了通过改变接收装置、控制电场和附加磁场等方法,改进静电纺丝技术来制取连续取向的纳米纤维,并对各种方法进行了简单的评价,指出磁化静电纺丝(MES)是目前制备取向纳米纤维最具有发展前景的方法.简要介绍了取向纳米纤维在生物组织工程领域方面的应用,并对其未来作了展望.     

静电纺丝法制备新型吸附分离材料

随着现代经济、工业的发展,许多环境问题出现在了人类面前,对于新型吸附分离材料的需求也变得十分迫切。静电纺丝法是一种简单有效制备连续纳米长丝的技术,有着十分广阔的应用前景。由于静电纺丝法制备的纤维膜具有较大的比表面积、易于调控的微观结构及化学性质,静电纺丝法能够用于制备新型的吸附分离材料。本文对电纺纤维膜的制备与改性,以及电纺纤维膜在空气过滤、油水分离、重金属离子去除等领域的应用进行了介绍,同时对其未来的发展进行了展望。     

基于静电纺丝技术的多级结构聚合物纳米纤维复合材料的研究进展

静电纺丝技术是目前制备纳米纤维最重要的方法之一,以其制备的纤维具有直径可控、比表面积大、孔隙率高等优点,因而被广泛应用于过滤、催化、传感器及生物医学等众多领域.以静电纺丝纤维为模板可进一步构建多级结构的功能性聚合物纳米纤维复合材料,拓宽其应用范围.本文着重概述了近年来基于静电纺丝技术的简单共混型、核壳结构及多级结构的聚合物纳米纤维复合材料的制备、结构及性能,并展望了其应用研究前景.     

胶原静电纺丝研究进展

胶原是细胞外基质的主要结构蛋白,广泛存在于各类动物机体中。天然胶原存在纤维形态不一、机械性能差等不足,限制了其工业规模化应用。因此,如何有效地制备出性能优良的胶原材料成为热点问题。静电纺丝技术是一种新兴的纳米材料制造技术,利用该技术可获得具有不同结构和性能的胶原基纳米纤维材料,制成的纳米纤维材料展现出密度低、弹性高等优异特性,有望广泛应用于组织工程、医学、载体等领域。本文将从胶原的单独静电纺丝及其影响因素、胶原共混静电纺丝和影响因素以及应用等方面介绍胶原静电纺丝技术的研究进展,并针对存在的问题和发展方向进行了讨论和展望,为胶原的应用提供一定的理论指导和技术支撑。     

静电纺丝制备醋酸纤维素复合纳米纤维的研究进展

静电纺丝技术就是通过带电聚合物溶液或熔体的喷射来制备纳米纤维,是一种制备纳米纤维材料简单有效的技术。醋酸纤维素(CA)易溶于有机溶剂,常作为纤维素的替代材料应用于静电纺丝领域。本文总结了近年来国内外采用静电纺丝技术制备CA复合纳米纤维的研究新进展,重点介绍了CA/CNTs复合纳米纤维、CA/金属粒子复合纳米纤维、CA/金属氧化物复合纳米纤维、CA基载药复合纳米纤维、CA/PAN复合纳米纤维、CA/PVA复合纳米纤维、CA/CS复合纳米纤维等CA复合纳米纤维的研究进展以及潜在的应用领域。     

静电纺丝纳米纤维薄膜的应用进展

静电纺丝是一种简单而高效制备高分子微纳米纤维的技术,由于设备和实验成本低、纤维产率高、制备出的纤维比表面积比较大、适用性广泛等独特的优势,近些年来备受关注。静电纺丝的应用是静电纺丝研究的最基本动力和终极目标,因此成为研究者一直努力的方向。为了研究静电纺丝应用的研究现状和主要发展方向,本文综述了静电纺丝纳米纤维薄膜几个主要的应用领域,包括组织工程、药物缓释、纳米传感器、能源应用、生物芯片和催化剂负载等,并展望了未来可能的发展方向。     

C60甲苯介质聚结动力学研究

应琦琮等[1]研究了C60-溶液的聚结动力学,发现在质量浓度0.78～1.29 mg*mL-1和室温(23 ℃～27 ℃)时为慢聚结.用分形理论得到维数为2.1;流体力学半径Rh＝(0.64±0.01) nm;Meidine等[2]用X射线测定C60苯溶剂化的单晶(结构是C60*4C6H6,苯环平行于C60分子表面),溶剂苯中心到C60的距离为0.67～0.68 nm,与文献[1]的结果很接近.     

Numerical simulation of droplet coalescence behavior in gas phase under the coupling of electric field and flow field

The coalescence behavior of droplets in an electric field belongs to the important research contents of electrohydrodynamics. Based on the phase field method of the Cahn–Hilliard equation, the electric field and the flow field are coupled to establish the numerical model of twin droplet coalescence in a coupled field. The effects of flow rate, electric field strength, droplet diameter, and interfacial tension on the coalescence behavior of droplets during the coalescence process were investigated. The results show that the dynamic behavior of the droplets is divided into coalescence, after coalescence rupture, and no coalescence under the coupling of electric field and flow field. The proper increase of the electric field strength will accelerate the coalescence of the droplets, and the high electric field strength causes the droplets to burst after coalescence. Excessive flow rates make droplets less prone to coalescence. Under the coupling field, the larger the droplet interface tension, the smaller the droplet diameter, the smaller the flow rate, and the shorter the droplet coalescence time. The results provide a theoretical basis for the application of electrostatic coalescence in gas–liquid separation technology.     

Molecular dynamics simulation on influence of temperature effect on electro-coalescence behavior of nano-droplets

In electric dehydration of crude oil, the dewatering efficiency can be improved by raising emulsion temperature properly which reduces the viscosity of crude oil. However, it should be noticed that the emulsion temperature does not only affect the emulsion viscosity but also nano-droplets dynamics behavior which impacts the coalescence efficiency either. Therefore the influence of temperature effect on the electro-coalescence of nano-droplets is studied by a molecular dynamics method. The results show that the temperature presents an active or negative effect, depending on the competitive relation between electrostatic interaction and thermal motion. Two stages are distinguished according to the dominant mechanism. During stage I, governed by the electrostatic interaction, lower temperature promotes the polarization and leads to an acceleration of the droplets coalescence, but higher temperature restrains the coalescence process due to molecules thermal motion breaking the polarization process. During stage II, governed by the thermal motion, lower temperature improves the coalescence because of a diffusion effect, but higher temperature deteriorates electro-coalescence because of a violent molecular thermal motion. Additionally, hydrogen bond and radial distribution functions are obtained by statistics to describe droplets micromorphology, which explains the reason why the droplet forms longer chain structure at the critical electric field.     

Numerical simulation of deformation behavior of droplet in gas under the electric field and flow field coupling

The water droplets in the process of electrostatic coalescence are important when studying electrohydrodynamics. In the present study, the electric field and flow field are coupled through the phase field method based on the Cahn–Hilliard formulation. A numerical simulation model of single droplet deformation under the coupling field was established. It simulated the deformation behavior of the movement of a droplet in the continuous phase and took the impact of droplet deformation into consideration which is affected by two-phase flow velocity, electric field strength, the droplet diameter, and the interfacial tension. The results indicated that under the single action of the flow field, when the flow velocity was lower, the droplet diameter was greater as was the droplet deformation degree. When the flow velocity was increased, the droplet deformation degree of a small-diameter droplet was at its maximum size, the large-diameter droplet had a smaller deformation degree, and the middle-diameter droplet was at a minimum deformation degree. When the flow velocity was further increased, the droplet diameter was smaller, and the droplet deformation degree was greater. Under the coupled effect of the electric field and flow field, the two-phase flow velocity and the electric field strength were greater, and the degree of droplet deformation was greater. While the droplet diameter and interfacial tension were smaller, the degree of droplet deformation was greater. Droplet deformation degree increased along with the two-phase flow velocity. The research results provided a theoretical basis for gas–liquid separation with electrostatic coalescence technology.     

Restoring of A balance by electric pulses

Restoring of the balance beam to its initial situation after a change of load can be effected by combination of forces of different kind. In former papers we discussed the possibility using the equation of motion of the balance to determine the mass to be measured. After the measurement the balance was restored by means of current pulses into the electromagnetic measuring system. In the present paper we discuss the application of electric pulses into an additional electrostatic system. This revised version was published online in July 2006 with corrections to the Cover Date.     

油水分离用超疏水纤维素基织物的制备及研究进展

近年来,石油泄漏和有机污染物排放对海洋环境和人类健康造成了严重的危害,开发高效、耐用的油水分离材料处理含油废水势在必行。纤维素基织物由于其多孔性、可再生性及优异的柔韧性在油水分离材料的制备中受到广泛的关注。本文详细介绍和讨论了各种不同方法制备超疏水纤维素基织物的研究现状,并阐述了超疏水纤维素基织物在油水分离中的应用,最后总结和展望了超疏水纤维素基织物在油水分离应用中待解决的问题和未来的研究方向。     

Effects of Applied Electric Fields on Drop—Interface and Drop—Drop Coalescence*

In this work, coalescence of a single organic or aqueous drop with its homophase at a horizontal liquid interface was investigated under applied electric fields. The coalescence time was found to decrease for aqueous drops as the applied voltage was increased, regardless of the polarity of the voltage. For organic drops, the coalescence time increased with increasing applied voltage of positive polarity and decreased with increasing applied voltage of negative polarity. Under an electric field, the coalescence time of aqueous drops decreases due to polarization of both the drop and the flat interface. The dependency of organic drop-interface coalescence on the polarity of the electric field may be a result of the negatively charged organic surface in the aqueous phase. Due to the formation of a double layer, organic drops are subjected to an electrostatic force under an electric field, which, depending on the field polarity, can be attractive or repulsive. Pair-drop coalescence of aqueous drops in the organic phase was also studied. Aqueous drop-drop coalescence is facilitated by polarization and drop deformation under applied electric fields. Without applied electric fields, drop deformation increases the drainage time of the liquid film between two approaching drops. Therefore, a decrease in the interfacial tension, which causes drop deformation, accelerates drop-drop coalescence under an electric field and inhibits drop coalescence in the absence of an electric field.     

Electrodipping force acting on solid particles at a fluid interface

We report experimental results which show that the interfacial deformation around glass particles (radius, 200-300 microm) at an oil-water (or air-water) interface is dominated by an electric force, rather than by gravity. It turns out that this force, called for brevity "electrodipping," is independent of the electrolyte concentration in the water phase. The force is greater for oil-water than for air-water interfaces. Under our experimental conditions, it is due to charges at the particle-oil (instead of particle-water) boundary. The derived theoretical expressions, and the experiment, indicate that this electric force pushes the particles into water. To compute exactly the electric stresses, we solved numerically the electrostatic boundary problem, which reduces to a set of differential equations. Convenient analytical expressions are also derived. Both the experimental and the calculated meniscus profile, which are in excellent agreement, exhibit a logarithmic dependence at long distances. This gives rise to a long-range electric-field-induced capillary attraction between the particles, detected by other authors. Deviation from the logarithmic dependence is observed at short distances from the particle surface due to the electric pressure difference across the meniscus. The latter effect gives rise to an additional short-range contribution to the capillary interaction between two floating particles. The above conclusions are valid for either planar or spherical fluid interfaces, including emulsion drops. The electrodipping force, and the related long-range capillary attraction, can engender two-dimensional aggregation and self-assembly of colloidal particles. These effects could have implications for colloid science and the development of new materials.     

Synergistic effect of silica nanoparticles and charged surfactants in the formation and stability of submicron oil-in-water emulsions

The influence of hydrophilic silica nanoparticles on the emulsification of a triglyceride oil (Miglyol812) in the presence of charged surfactants (lecithin or oleylamine) and the long term stability of the resultant oil-in-water emulsions are reported. A synergistic effect of nanoparticles and surfactants in improving emulsification and stability to coalescence is evident only when the silica nanoparticles are initially added to the oil phase. When nanoparticles are included from the water phase, no synergistic stabilisation was observed due to electrostatic bridging or unfavourable attachment due to the repulsive electrostatic and hydration forces. Free energies of adsorption for silica nanoparticles at the oil-water interface calculated from experimentally determined interfacial tensions and three phase contact angles can be correlated to long-term emulsion stability only when silica is added from oil phase.     

A visible coalescence of droplets on hydrophobic and hydrophilic fibers in water-in-oil emulsion

The droplets’ coalescence is instantaneous and rather complex in emulsion. The theoretical analysis of this process was presented by a former research, while visible experiments to verify these are still scarce. This work aims to show and analyze the visible water droplets’ coalescence on hydrophobic bamboo charcoal fibers and hydrophilic glass fibers in water-in-oil emulsion. An experimental setup with microscope and high-speed camera was designed and established to record the water droplets’ coalescence. The water droplets’ collision coalescence on bamboo charcoal fibers was observed, and the diameters of water droplets detaching from the fibers with different angles were measured. The angle between the fiber and the flow velocity can affect the diameters of water droplets detaching from the bamboo charcoal fibers, and cross-fibers can the enormously increase water diameters compared with single fiber. Meanwhile, the water droplets’ collision coalescence on glass fibers was observed and the result shows that the collision coalescence also occurred on the hydrophilic glass fibers when the droplet diameter was small. In addition, other factors, including flow velocity and droplets’ diameter for the coalescence on the hydrophilic glass fibers were investigated.     

FRAGMENTATION OF PRIMARY FLOCS IN EMULSIONS AND THE SUBSEQUENT REDUCTION OF COALESCENCE

In existing theories emulsion desiabilization is considered as the combined processes of irreversible flocculation and coalescence of dispersed droplets. This approach can be justified when the potential pit characterizing the energy of droplet interaction is sufficiently deep, i.e. excluding small droplet dimensions, strong electrosiatic repulsion and low electrolyte concentrations. For smaller droplet dimensions and stronger electrostatic repulsions the emulsion instability must be considered as a combined process of reversible flocculation and coalescence. In this paper a mathematical model that couples the kinetics of flocculation, coalescence and floe fragmentation is developed in order to quantify the kinetic instability of emulsions with charged submicron droplets. The characteristic limes for flocculation (Smoluchowski's time τ_c) for coalescence (coalescence time τ_c) and for disaggregation (doublet lifetimeτ_d) are considered model parameters. The mathematical model applies to the case when and τ_d<< τ_c, which corresponds to a situation with a small multiplet concentration compared to the concentration of doublets and a singlet-doublet quasi-equilibrium. It is established that at singlet-doublet quasi-equilibrium the rate of the decline in the total droplet concentration is described by second order kinetics in distinction to the exponential time dependence valid for coalescence at irreversible flocculation. The double disintegration reduces the entire coalescence rate, expressed as τ_sm/ τ_d. This reduction is very large at small values of Td. The mathematical model presented can hased on the spontaneous disintegration of doublets predict changes in emulsion stability for model systems and also for technologically important emulsions.