Time Evolution of the Wettability of Supported Graphene under Ambient Air Exposure.
Time Evolution of the Wettability of Supported Graphene under Ambient Air Exposure.
复制标题
DOI：
10.1021/acs.jpcc.5b10492
复制
发表时间：
2016-02-04
期刊：
影响因子：
--
通讯作者：
Hofmann S
中科院分区：
文献类型：
--
作者：
Aria AI;Kidambi PR;Weatherup RS;Xiao L;Williams JA;Hofmann S
石墨烯的润湿性对于大多数应用中的接口来说既基本又至关重要，但对其时间演变的详细了解仍然难以捉摸。在这里，我们使用水和具有广泛不同表面张力的各种其他测试液体，系统地研究了金属支撑的化学气相沉积石墨烯薄膜的润湿性，作为环境空气暴露时间的函数。石墨烯的润湿性不是恒定的，而是随着基底相互作用和空气暴露时间而变化。基底相互作用会影响初始石墨烯的润湿性，例如，在暴露于空气几分钟后，镍和铜支撑的石墨烯的水接触角分别为~85°和~61°。对表面自由能成分的分析表明，基底相互作用强烈影响负载石墨烯的路易斯酸碱成分，而镍负载石墨烯的路易斯酸碱成分比铜负载石墨烯弱得多，这表明仅经典范德华相互作用理论不足以描述石墨烯的润湿性。对于长时间暴露在空气中，空气污染物的物理吸附作用变得越来越占主导地位，导致水接触角增加，与暴露时间呈普遍的线性对数关系，直到在最大值 92-98° 处饱和。吸附的污染物使所有支持的石墨烯样品变得越来越非极性，尽管它们的总表面自由能仅下降 10-16% 至约 37-41 mJ/m2。我们的发现表明，未能考虑空气暴露时间可能会导致润湿性值差异很大，并导致有关石墨烯润湿透明度的矛盾争论。
The wettability of graphene is both fundamental and crucial for interfacing in most applications, but a detailed understanding of its time evolution remains elusive. Here we systematically investigate the wettability of metal-supported, chemical vapor deposited graphene films as a function of ambient air exposure time using water and various other test liquids with widely different surface tensions. The wettability of graphene is not constant, but varies with substrate interactions and air exposure time. The substrate interactions affect the initial graphene wettability, where, for instance, water contact angles of ∼85 and ∼61° were measured for Ni and Cu supported graphene, respectively, after just minutes of air exposure. Analysis of the surface free energy components indicates that the substrate interactions strongly influence the Lewis acid–base component of supported graphene, which is considerably weaker for Ni supported graphene than for Cu supported graphene, suggesting that the classical van der Waals interaction theory alone is insufficient to describe the wettability of graphene. For prolonged air exposure, the effect of physisorption of airborne contaminants becomes increasingly dominant, resulting in an increase of water contact angle that follows a universal linear-logarithmic relationship with exposure time, until saturating at a maximum value of 92–98°. The adsorbed contaminants render all supported graphene samples increasingly nonpolar, although their total surface free energy decreases only by 10–16% to about 37–41 mJ/m2. Our finding shows that failure to account for the air exposure time may lead to widely different wettability values and contradicting arguments about the wetting transparency of graphene.