超声波振动静电纺纳米纤维控制增强及其力学模型研究

Electrospinning is one of the highlighted techniques for research and development of nanofibers, and its strategic significance has been recognized by the whole world since the earliest of 20th century.However the development and commercialization of electrospinning have been seriously impeded by the fragility of its products due to its working principle. Electrospun nanofibers are produced by using high electric force to break the surface tension of the polymer solution at the tip of a capillary, drawing a jet out of the solution and thinning the jet down to nanosize throuh a highly instable whipping motion of the jet itself. Electrospinning cannot be applied to a solution with a high viscosity since it will be too hard for the electric force to overcome the surface tension of the solution. And during spinning, a highly instable whipping motion of electrospinning jet will inevitable occur due to the uneven distribution of electrical charge in and on the surface of the jet. These two characters destine electrospun nanofibers to lose arrangement of the molecular chains in the structure, high proportional defects and the fragility in mechanical property. To challenge the perplexity, we designed an ultrosonic vibration coupled electrospinning setup. With this ultrasonic vibration electrospinning technology, we realized the electrospinning of high viscous polymer solutions and proved the improvement of the crystallization structure of the nanofibers through experiments. In this project, we propose to theoretically deepen our research by investigating the working rules of ultrosonic vibration on the whipping motion of electrospinning jet, analyzing effects of ultrasonic vibration on crystallization process, crystal structure, allignment of molecular chains of the obtained fibers, and modelling the electrospinning process with consideration of the effects of ultrasonic vibration on the current, momentum and energy balance of the jet. Based on these research,we'll try to optimize the ultrasonic vibration electrospinning process to make stronger nanofibers. Succeed in this porject will not only help us theoretically understand this new technology, but also will advance current theoretical models of electrospinning, propel the development of electrospinning technology. Furthermore, it may break the hamper that prevent electrospinning from commercialization with the succeess in producing strong nanofibers.

静电纺丝技术是纳米纤维的焦点研发技术之一，具有国际战略地位。但因其原理限制，静电纺丝技术无法对高粘度溶液纺丝且纺丝过程存在高度不稳定鞭动行为，造成纤维大分子结构松散、缺陷过多、机械强度过低的问题，成为静电纺丝技术的工业化发展瓶颈。利用超声波振动场的叠加可实现高粘度溶液的静电可纺，改变射流行为，改善纤维内部结构。因此，本项目拟深入研究超声波振动对静电纺丝射流行为的影响规律，分析超声波振动对静电纺纳米纤维结晶过程、结晶结构和分子链段取向等的影响规律及作用机理，并在此基础上通过参数优化实现纳米纤维机械性能的优化调控，同时我们还将从力学角度分析超声波振动力场的叠加对静电纺丝射流的电流、动量及能量平衡的影响模式，构建适用于超声波振动静电纺丝技术的力学模型，不仅为超声波振动静电纺丝技术的发展奠定基础，而且还将解决静电纺丝技术的瓶颈问题，制得高强度静电纺纳米纤维，推动静电纺技术的工业化应用。

静电纺丝技术是纳米纤维的焦点研发技术之一，具有国际战略地位。但因其原理限制，静电纺丝技术纺丝对象为高溶液含量的低粘度聚合物溶液，无法对高浓度/粘度溶液进行纺丝，造成了成纤的大分子结构松散、缺陷过多、机械强度过低的问题，成为静电纺丝技术的工业化发展瓶颈。利用超声波振动场的叠加可实现改善高浓度/粘度聚合物溶液的流变性能，实现高粘度溶液的静电可纺，改变射流鞭动行为，减小纤维细度，改善纤维内部大分子结构。本项目深入研究了超声波振动对高浓度/粘度静电纺丝溶液流变性能的影响规律，及其对静电纺射流鞭动行为的影响，分析超声波振动对静电纺纳米纤维直径、表面形态、内部结构、大分子结构包括结晶结构和分子链段取向，以及纤维膜孔隙结构特征等的影响规律及作用机理，并在此基础上通过参数优化实现了纳米纤维机械性能的优化提高。我们的研究表明，超声波振动可以改善静电纺丝溶液的流变性能，降低溶液的粘度和表面张力，提高溶液的电导率，从而影响射流的泰勒锥形态及鞭动幅度，扩大聚合物溶液静电可纺范围，降低纤维细度，提高纤维密度，在不改变分子化学结构的情况下显著改善纤维表面及内部结构，提高纤维结晶度，从而显著提高纤维机械性能。在最优振动条件下，静电纺18%PAN纤维的密度可以从无振动时的1.0365 g/cm3提高到1.4936 g/cm3，纤维膜的初始模量由原来的0.1746 N/m2迅速增至8.5513 N/m2，断裂强度从2.71 MPa提高到16.17 MPa，增幅高达6倍。对超高分子量聚乙烯纤维束断裂强度的增强效果也超过2倍以上。针对这种新型纺丝技术，我们还从力学角度分析了超声波振动力场的叠加对静电纺丝射流的电流、动量及能量平衡的影响模式，构建了适用于超声波振动静电纺丝技术的力学模型。此外，为了方便静电纺纳米纤维的力学性能研究，我们建立了静电纺纳米纤维膜的理想单胞，并通过几何分析，构建了单根静电纺纳米纤维与纳米纤维膜之间的机械性能数学模型。该研究不仅在解决静电纺丝技术的强力瓶颈问题上取得了突破，制得高强度静电纺纳米纤维，而且为超声波振动静电纺丝技术的研究发展奠定了基础，可有效推动静电纺产品的进一步工业化应用。