由于水凝结到泰勒锥中而导致电纺丝破裂。,ACS Applied Materials & Interfaces

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由于水凝结到泰勒锥中而导致电纺丝破裂。
ACS Applied Materials & Interfaces ( IF 8.3 ) Pub Date : 2020-05-18 , DOI: 10.1021/acsami.0c03338
Catherine G Reyes ₁ , Jan P F Lagerwall ₁

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在潮湿空气中将吸湿性聚合物纤维静电纺丝的众所周知的问题通常归因于水在飞行中途冷凝到水上：水以附加溶剂的形式进入水射流，阻碍了固化成纤细的纤维。在这里，我们表明，如果溶剂易挥发且可与水（例如乙醇）混溶，则在过程结束时看到的纤维熔合和形变实际上可能是由已经冷凝到泰勒锥中的水所致。即使水本身是可接受的溶剂，添加水也可以从根本上将溶剂的特性从好变为差。而且，与直觉相反，由于通过相变以及放热混合过程释放的热量，水的冷凝促进了溶剂的蒸发。总体结果是，聚合物溶液在泰勒锥周围形成了凝胶状的皮肤。如果注入的芯液与聚合物鞘层溶剂和空气中的冷凝水一起形成具有可混溶间隙的复数相图，则在同轴电纺以制造功能性复合纤维的情况下，情况会更加恶化。当具有不同组成的液滴成核并扩散时，所形成的相分离会在整个泰勒锥上凝结聚合物，从而建立了强大的内部流动和浓度梯度。我们证明了这些不受控制的聚合物凝结的情况会导致泰勒锥快速变形，多次喷射以及无法旋转同轴纤维毡，

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Disruption of Electrospinning due to Water Condensation into the Taylor Cone.

The well-known problems of electrospinning hygroscopic polymer fibers in humid air are usually attributed to water condensing onto the jet mid-flight: water enters the jet as an additional solvent, hindering solidification into well-defined fibers. Here, we show that fiber fusion and shape loss seen at the end of the process may actually stem from water already condensing into the Taylor cone from where the jet ejects, if the solvent is volatile and miscible with water, for example, ethanol. The addition of water can radically change the solvent character from good to poor, even if water on its own is an acceptable solvent. Moreover, and counterintuitively, the water condensation promotes solvent evaporation because of the release of heat through the phase transition as well as from the exothermic mixing process. The overall result is that the polymer solution develops a gel-like skin around the Taylor cone. The situation is significantly aggravated in the case of coaxial electrospinning to make functional composite fibers if the injected core fluid forms a complex phase diagram with miscibility gaps together with the polymer sheath solvent and the water condensing from the air. The resulting phase separation coagulates the polymer throughout the Taylor cone, as liquid droplets with different compositions nucleate and spread, setting up strong internal flows and concentration gradients. We demonstrate that these cases of uncontrolled polymer coagulation cause rapid Taylor cone deformation, multiple jet ejection, and the inability to spin coaxial fiber mats, illustrated by the example of coaxial electrospinning of an ethanolic polyvinylpyrrolidone solution with a thermotropic liquid crystal core, at varying humidities.

更新日期：2020-05-18

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