纳米界面作用下等离子体改性时效性的正电子研究

The clean, fresh water in the world is not enough for all the uses, whether agricultrue, industrial or domestic, but the water demand continues to rise due to the increase of population. Membrane separation is a novel technique, which can be used for obtaining fresh water from sea water, saline water and so on. In order to develop the membrane exhibiting even better performance (higher water flux), the hydrophilicity of the membrane surface need to be improved. Plasma modification is a unique method to improve the surface properties of non-polar polymers, but the improved properties usually decay with storage time which is called as the durability of plasma modification. . In this work, EVA nanocomposites with different nano-interfaces are prepared, and the nanocomposite surfaces are modified by plasma. Positron lifetime annihilation measurement is utillized to probe the free-volume hole in the nanocomposites. The correlation between the free volume property and the durability of the surface wettabiliy is to be studied. Positron annihilation gamma ray spectroscopy coupled with positron beam is applied to monitor the movement of the polar group in EVA nanocomposite surface after plasma modification.. According to the effect of the nano-interface on the durability of the plasma modification, which is explained by positron results, a novel method that can control the durability by nanostructure is expected to be developed. The influence mechanism by the nano-interface can support the development of the polymer membrane surface functionalization, and be useful for the water treatment by membrane technique in the future.

膜分离技术是最具发展潜力的水处理方法。为得到同时具有较高截留特性和纯水通量的高分子膜，需提高膜表面的亲水性。等离子体技术能快速高效的改善高分子膜表面的亲水性，但该性能会随时间的推移而衰减。这种时效性问题是制约等离子体技术在高分子膜表面功能化的主要瓶颈。.本项目以乙烯-醋酸乙烯酯共聚物（EVA）为研究对象，在材料中构筑不同类型的纳米界面，利用等离子体改善纳米复合膜表面的亲水性，借助慢正电子束技术监控膜表面亲水性的极性基团其迁移行为，根据正电子寿命谱学结果，探究自由体积特性与等离子体处理时效性的关系，并从分子链段运动的微观角度阐明时效性的机理及其影响因素。.本项目旨在利用正电子技术揭示纳米界面对等离子体表面改性的时效性的影响机理，从而可通过改变材料的纳米结构来调控时效性的强弱，调控材料的表面性能，进而为高分子膜表面功能化的开发提供理论支撑，为推动水处理技术的发展奠定基础。

为了得到具更好性能的高分子基分离膜，利用正电子湮没技术对纳米结构膜材料表面等离子体改性憎水恢复性机理进行了研究。研究内容：（1）高分子/层状硅酸盐纳米复合材料的制备；（2）聚烯烃、硅橡胶等不同材料等离子体表面改性憎水恢复性机理的研究；（3）等离子体改性增强分离膜表面抗污染性能的探索。. 研究发现了在熔融加工过程中，EVA材料中的醋酸乙烯酯基团的浓度能显著影响EVA在热剪切作用下的降解性能，累托土纳米片层的引入可显著增强EVA材料在高温下剪切的抗降解能力；根据正电子寿命谱结果发现，纳米片层的引入可增加了复合材料的界面，而纳米复合材料的熔融指数随纳米片层浓度的增加而增大，可认为这些纳米界面作为复合材料熔体中的润滑剂加大了熔体的流动性；慢正电子束结果证实，等离子体改性后的憎水恢复性与聚烯烃表面分子链段上极性基团的迁移相关，而憎水恢复性的实验结果可利用Fick第二定律进行较好的拟合，故聚烯烃表面的憎水恢复性是由于等离子体改性后表面极性基团向内部扩散，而硅橡胶表面的憎水恢复性是由于材料内部疏水小分子向表面扩散；等离子体技术应用于聚砜/二氧化钛分离膜的表面改性，显著增强了分离膜的水通量以及表面抗污染能力。. 项目结果从微结构的角度，阐明了等离子体改性技术对高分子薄膜材料的影响机制、效果。并将该技术应用于分离膜表面改性，提高了其水通量，增强了其表面抗污染性能，为进一步利用等离子体技术开发新型分离膜，提供了初步的理论依据和实验结果。