有气体溶解和没有气体溶解的水中石墨烯间的疏水引力

凝聚物理学界发现溶解在水中的气体会在疏水表面吸附,由此认为当疏水物体间距足够小的时候,吸附在疏水表面的气体会相互联通形成纳米气泡桥,纳米气泡桥连结疏水物质形成疏水引力,但是关于纳米气泡桥的形成过程和形态,力学界还没有一个清晰的描述.采用分子动力学方法,研究了在有气体溶解的水中和没有气体溶解的水中两片石墨烯间的引力作用,分析了两种情况下各相密度分布的变化过程、结构相图的变化过程和平均力势的变化过程,详细阐明了纳米气泡桥的形成和消失过程,并定量计算了纳米气泡桥的作用效果和作用距离.模拟结果表明:两片石墨烯在有气体溶解的水中和无气体溶解的水中的疏水引力都是由纳米气泡桥引起的.当石墨烯间距小于0.5nm时,无论水中是否有气体溶解,疏水引力由真空纳米气泡桥引起;当石墨烯间距大于0.5nm时,在没有气体溶解的水中,疏水引力由水蒸气纳米气泡桥引起;而在有气体溶解的水中,疏水引力由所溶气体形成的纳米气泡桥引起. 

HYDROPHOBIC ATTRACTION OF GRAPHENE IN LIQUID WATER WITH AND WITHOUT GAS

The phenomenon that the gas dissolved in water can be adsorbed and accumulated on the hydrophobic surface is discovered by condensed matter physics. Thus, when the distance between the hydrophobic objects is small enough, the gases adsorbed on the hydrophobic surfaces will connect each other and form nanobubble bridges. The nanobubble bridges cause hydrophobic attraction. However, the formation/disappearance process and the morphology of nanobubble bridges have not been provided in academe of mechanics. In this article, the interactions of a pair of graphene in liquid water with and without gas phase are studied using molecular simulation. The changes of structural phase diagram and potential of mean force of the system, the density distribution of gas and water were analyzed. The results show that the hydrophobic attraction of two pieces of graphenes is really caused by the nanobubble bridge. When the distance between the pair of graphenes is less then approximate 0.5 nm, hydrophobic attraction is led by vacuum nanobubble bridge no matter with or without gas phase in water. When their distance is greater than approximate 0.5 nm, the hydrophobic attraction without gas in water is led by the nanobubble bridge of vapor, and the hydrophobic attraction with gas in water is led by the nanobubble bridge of the gas.