材料表面结构对其自清洁超疏油性能的影响

A material surface having a oil contact angle greater than 150 degree and a very low roll-off angle is called a superoleophobic surface. Self-cleaning is so termed as oil easily rolls off a superoleophobic surface taking away dirt. Self-cleaning superoleophobic materials have a wide applicability in various fields, including clothing,carpets,microfluids,no lost transport of liquid. Compared with water, oils, such as vegetable oil and most machine oils, have lower surface tension and more easily wet solid surfaces. It is found that high contact angles can be obtained by combined treatments with low surface tension chemical agents and increasing surface roughness. Since most smooth material surfaces are oleophilic, for instance, the contact angle of dodecane on PTFE (-CF2- which has low surface energy) is around 40 , it is impossible to deliver superoleophobicity to a smooth surface only through treatments with low surface tension chemical agents. Therefore, surface roughness becomes one of the important factors for superoleophobic materials. The objective of this research is to investigate the influences of surface roughness on self-cleaning superoleophobic properties of materials. The shape,size,and distribution of single bodies which make a surface rough are considered in this research. The study could be achieved based on the thermodynamic theory, the adhesive energy between solid and liquid surfaces, and the maximum pressure which a rough surface can hold to prevent liquid breakthrough. According to the thermodynamic theory, a system prefers a state at which it has lower Gibbs free energy. The adhesive energy between solid and liquid surfaces is decided by the contact area and the surface tension between solid and liquid. Lower contact area can reduce the adhesion between liquid and solid surface. Liquid on solid surfaces which have different roughness should have different Gibbs free energies, adhesive energies and breakthrough pressures. The ranges of roughness of solid surfaces could be found for self-cleaning superoleophobic materials through comparing the Gibbs free energies, adhesive energies and breakthrough pressures of desinged material surfaces. The study would provide theoretical support for design and preparation of self-cleaning superoleophobic materials (e.g. fabrics).

自清洁超疏油材料在纺织服装品、家居装饰物、地毯、微流体、无损液体传输等领域有着广泛的应用前景。疏油材料可以通过降低材料表面能量与适当地调整材料表面粗糙程度实现。但是迄今为止，关于自清洁超疏油材料的理论研究在国内外都鲜有报道（特别是对表面张力低于25mN/m的油）。本项目拟研究材料表面粗糙程度对其自清洁超疏油性能的影响，即：通过设计具有不同表面粗糙程度的几何模型，比较液体在不同模型体系的吉布斯自由能、液体与几何个体的接触面积（固液黏附能）、以及液体自身产生的压强与粗糙程度不同的材料表面所能承受的最高防止液体润湿压强，运用数学推导和模拟，在理论上得到具有较低或最低系统吉布斯自由能、固液黏附能（固液接触面积）和较高防止液体润湿压强的粗糙材料表面上的几何个体所应具有的形状、尺寸和分布等的范围。该项目将为自清洁超疏油材料（特别是纤维纺织品）的研究与制备提供理论依据和指导方向。

水和油与人类的生活密不可分，例如，衣服、房间装饰物及地毯容易沾染食物中的油脂，撒落的农药会通过服装与农民的皮肤接触，沾在军用服上的生化液会威胁到士兵的生命安全等。所以，研究和开发具有自清洁性能的超疏水疏油材料是非常必要的。迄今为止，疏油材料的研究主要集中于提高油在材料表面的接触角，但是关于材料表面结构对其超疏水疏油的研究较少。本课题通过能量与压强分析的方法，研究材料表面结构（材料表面粗糙物的几何形状、尺寸、分布等）对材料自清洁性能的影响，为自清洁超疏油材料（纤维）的研究与制备提供理论依据和指导方向。研究发现液滴在圆柱形几何物体上处于一个稳定的状态（没有自发运动的趋势）；而在圆锥上时，由于圆锥直径由底面到顶点减小，液滴位于圆锥尖端方向的油-气界面的压力要大于位于圆锥底面方向的油-气界面的压力。该压力差会产生使油滴沿着圆锥由尖端向底面移动的趋势。研究发现液体会沿着构成材料表面的几何个体（高度为h）下行一段距离。当下行距离等于粗糙物质高度时，液体触及底层，进而完全润湿材料；当下行距离小于粗糙物质高度而停止润湿的情况下，液面成弧线形。截留在固体和液体之间的空气有助于帮助抵御液体对固体的润湿。所以制备疏油自清洁材料，应注意材料的粗糙结构能使液体下行距离低于该粗糙物高度。研究发现，单位面积内粗糙几何体个数即微球分布必须超过一定密度，材料才能具备自清洁超疏水、疏油性能。研究还发现，单阶粗糙尺寸（即同一尺寸几何体）对材料的自清洁超疏油性能的提高有限，多阶粗糙（如微纳米复合微球）更加有利于该性能的提高。本课题通过对材料表面结构的探讨，为自清洁超疏油领域的研究提供理论依据，并为材料的选材与后加工提供指导方向。