Upon closer inspection, it becomes

通过仔细检查，很明显静电纺丝过程非常复杂。例如，射流仅<br>沿一条通向对电极的直接路径一定距离，但随后会显着改变其外观。射流横向移动并形成一系列线圈，其包络线具有朝向反电极开口的丙酮的形式（图7）。[36,37] <br>有时在静电纺丝过程中会形成小珠而不是纤维。<br>也可以形成具有像珍珠一样排列在串上的珠子的纤维。在某些情况下，纤维不是圆形的，而是扁平的条带，在其他情况下，纤维直径的分布较宽（图8）。形状和<br>形成的纤维的尺寸取决于大量参数，例如，聚合物本身的特性（例如分子量，分子量分布，玻璃化转变温度和溶解度），以及聚合物溶液的特性（例如粘度，粘弹性，浓度，表面张力和电导率）。溶剂的蒸气压和环境的相对湿度也会产生重大影响。此外，基质的性质，溶液的进料速度以及电极的场强和几何形状（因此，电场形式）在纤维形成中起着重要作用。<br>2.2。理论背景<br>如上所述，静电纺丝过程非常复杂：它可以描述为几个物理不稳定性过程的相互作用。[36-39]考虑到液体股线（溶液或熔体）经历复杂的结构形成过程，即使不存在液体，这种复杂性也并不惊人。电场 股线遭受所谓的瑞利不稳定性。[40-43]最终状态是给定半径的液滴的周期性珍珠项链排列（图9）。在静电纺丝过程中，液体束与电场的耦合（通过场诱导的电荷向液体束的传输）会引起其他不稳定性，特别是所谓的轴对称不稳定性和弯曲（或搅打）不稳定性。[36-39]驱动轴对称不稳定性 射流半径的统计变化会引起表面电荷密度的调制。这种调制反过来会产生切向力，该切向力会耦合到半径调制并将其放大。这种耦合环的最终结果是形成珠子，这些珠子沿着纤维状排列<br>图5.用荧光素染色的聚环氧乙烷（PEO）的5％水溶液在水中的液滴：A）在没有施加电压的情况下；B）在20kV的施加电压下，垂直于对电极的射流；C）在20 kV的施加电压下，与对电极成对角线。<br>图6.左：通过熔融静电纺丝生产的聚酰胺（PA）纤维的SEM图。右：纤维的透射电子显微镜（TEM）图像

Upon closer inspection, it becomes clear that the electrospinning process is very complex. The jet, for instance, only<br>follows a direct path towards the counter electrode for a certaindistance,butthenchangesitsappearancesignificantly. The jet is moved laterally and forms a series of coils, the envelopeofwhichhastheformofaconeopeningtowardsthe counter electrode (Figure 7).[36,37]<br>On occasion, beads, rather than fibers, are formed during electrospinning; fibers with beads arranged like pearls on a<br>string can also be formed. In some cases, the fibers are not round,butareflat ribbons, andinothercases,thedistribution of fiber diameters is broad (Figure 8). The shapes and<br>dimensions of the fibers formed depend on a large set of parameters, for example, the properties of the polymer itself (such as molecular weight, molecular-weight distribution, glass-transition temperature, and solubility), as well the properties of the polymer solution (such as viscosity, viscoelasticity, concentration, surface tension, and electrical conductivity). The vapor pressure of the solvent and the relative humidity of the surroundings can also have a significant impact. Furthermore, the properties of the substrate, the feed rateofthesolution,andthefieldstrengthandgeometryofthe electrodes(andtherefore,theformoftheelectricfield)playa major role in fiber formation.<br>2.2. Theoretical Background<br>As mentioned above, the electrospinning process is very intricate: it can be described as the interaction of several physical instability processes.[36–39] This intricacy is not astounding, considering that a liquid strand (solution or melt)undergoescomplexstructure-formingprocessesevenin absence of an electric field; the strand is subjected to the socalled Rayleigh instability.[40–43] The final state is a periodic pearl-necklace arrangement of drops of a given radius (Figure 9). During electrospinning, other instabilities are induced by the coupling of the liquid strand with the electric field (throughthefield-inducedtransportofchargesintotheliquid strand), in particular, the so-called axisymmetrical instability and the bending (or whipping) instability.[36–39] Inthecaseofthecharge-drivenaxisymmetricalinstability, a statistical variance of the jet*s radius causes a modulation of thesurfacechargedensity.Thismodulation,inturn,generates tangential forces, which couple to the radius modulation and amplify it. The end result of such a coupling loop is the formation of beads, which are aligned along the fiber like<br>Figure 5. A droplet of a 5% solution of poly(ethylene oxide) (PEO) in water, dyed with fluorescein: A) in the absence of an applied voltage; B) at an applied voltage of 20 kV, with a jet perpendicular to the counter electrode; C) at an applied voltage of 20 kV, with a jet diagonal to the counter electrode.<br>Figure 6. Left: SEM image of fibers of polyamide (PA) produced by melt electrospinning. Right: Transmission electron microscope (TEM) image of fibers

经过仔细观察，很明显，静电纺丝过程是非常复杂的。例如，喷气式飞机<br>在一定的距离内，沿着一条直达对电极的路径，但变化显著。射流横向移动，形成一系列线圈，线圈的外壳朝着对电极方向打开（图7）。[36,37]<br>有时，在静电纺丝过程中会形成珠子，而不是纤维；在<br>也可以形成字符串。在某些情况下，纤维不是圆形的，而是扁平的带状物，而在其他情况下，纤维直径的分布很宽（图8）。形状和<br>所形成纤维的尺寸取决于一系列参数，例如聚合物本身的性质（例如分子量、分子量分布、玻璃化转变温度和溶解度），以及聚合物溶液的性质（例如粘度、粘弹性、浓度、表面张力，以及导电性）。溶剂的蒸汽压和周围环境的相对湿度也会产生重大影响。此外，基底的性质、溶液的进料速率和电极的电场强度（即电场强度）对纤维的形成起着重要的作用。<br>2.2条。理论背景<br>如上所述，静电纺丝过程是非常复杂的：它可以被描述为几个物理不稳定过程的相互作用。[36–39]考虑到液体链（溶液或熔体）在没有电场的情况下经历复杂的结构形成过程，这种复杂的过程并不令人吃惊；链受到所谓的瑞利不稳定性。[40-43]最终状态是由给定半径的水滴组成的周期性珍珠项链排列（图9）。在静电纺丝过程中，其他不稳定性是由液体链与电场的耦合（通过电场诱导电荷向液体链的传输）引起的，特别是所谓的轴对称不稳定性和弯曲（或鞭打）不稳定性，射流半径的统计变化引起表面电荷密度的调制，这种调制产生切向力，切向力与半径调制耦合并放大。这种耦合环的最终结果是形成沿纤维状排列的珠子<br>图5。聚环氧乙烷（PEO）5%溶液在水中的一滴，用荧光素染色：A）在没有施加电压的情况下；B）在施加电压为20千伏的情况下，用一个垂直于对电极的射流；C）在施加电压为20千伏的情况下，用一个与对电极成对角线的射流。<br>图6。左：熔融静电纺丝聚酰胺（PA）纤维的扫描电镜图像。右图：纤维的透射电子显微镜（TEM）图像<br>