Probing the critical nucleus size for ice formation with graphene oxide nanosheets
Probing the critical nucleus size for ice formation with graphene oxide nanosheets
复制标题
用氧化石墨烯纳米片探测冰形成的临界核尺寸
DOI：
10.1038/s41586-019-1827-6
复制
发表时间：
2019-12-19
期刊：
影响因子：
64.8
通讯作者：
Wang, Jianjun
中科院分区：
文献类型：
--
作者：
Bai, Guoying;Gao, Dong;Wang, Jianjun
水的冻结无处不在，影响着气候、化学工业、低温生物学和材料科学等各个领域。冰成核是水冻结的控制步骤（1-5），并且近世纪以来一直被认为需要形成临界冰核（6-10）。但是，由于其瞬态和纳米级的性质，没有直接的实验证据证明这种核的存在（6，7）。在这里，我们报告了在含有氧化石墨烯纳米片的控制尺寸的水滴中的冰成核，并表明它们仅在一定尺寸以上对冰成核有显着影响，该尺寸随液滴的过冷程度而变化。我们从我们的实验数据和理论计算中推断，氧化石墨烯的临界尺寸反映了临界冰核的尺寸，在足够大的氧化石墨烯位于其表面的情况下，临界冰核的尺寸引起与经典成核理论一致的冰形成行为。相比之下，当氧化石墨烯的尺寸小于临界冰核的尺寸时，在氧化石墨烯的外围处的钉扎使冰核随着其生长而变形。这导致用于成核的高得多的自由能势垒，并且抑制氧化石墨烯（11）的促进作用。这些结果提供了关于临界冰核的存在和温度依赖性大小的实验信息，以前只在理论上和通过模拟进行了探索（12-16）。由于在纳米颗粒边缘处的临界前核的钉扎并不特定于石墨烯氧化物上的冰核，我们期望我们的方法可以扩展到探测其他成核过程中的临界核。
Water freezing is ubiquitous and affects areas as diverse as climate, the chemical industry, cryobiology and materials science. Ice nucleation is the controlling step in water freezing(1-5) and has, for nearly a century, been assumed to require the formation of a critical ice nucleus(6-10). But there has been no direct experimental evidence for the existence of such a nucleus, owing to its transient and nanoscale nature(6,7). Here we report ice nucleation in water droplets containing graphene oxide nanosheets of controlled sizes and show that they have a notable impact on ice nucleation only above a certain size that varies with the degree of supercooling of the droplets. We infer from our experimental data and theoretical calculations that the critical size of the graphene oxide reflects the size of the critical ice nucleus, which in the case of sufficiently large graphene oxides sits on their surface and gives rise to ice formation behaviour consistent with classical nucleation theory. By contrast, when the graphene oxide size is smaller than that of the critical ice nucleus, pinning at the periphery of the graphene oxide deforms the ice nucleus as it grows. This gives rise to a much higher free-energy barrier for nucleation and suppresses the promoting effect of the graphene oxide(11). The results provide experimental information on the existence and temperature-dependent size of the critical ice nucleus, which has previously only been explored theoretically and through simulations(12-16). As pinning of a pre-critical nucleus at a nanoparticle edge is not specific to the ice nucleus on graphene oxides, we expect that our approach could be extended to probe the critical nuclei in other nucleation processes.