Skountzos Emmanuel N, Ravichandran Ashwin, Lawson John W
KBR Inc., Intelligent Systems Division, NASA Ames Research Center, Moffett Field, California 94035, United States.
Intelligent Systems Division, NASA Ames Research Center, Moffett Field, California 94035, United States.
Langmuir. 2024 Dec 24;40(51):26864-26874. doi: 10.1021/acs.langmuir.4c03106. Epub 2024 Dec 9.
Ice accumulation on aircraft surfaces poses significant safety and performance risks, necessitating the development of coatings to prevent ice adhesion. The present work focuses on characterizing the interfacial properties of ice on various substrates through molecular descriptors. We follow the hypothesis that has been previously proposed in several experimental works according to which a disordered, quasi-liquid layer (QLL) of water at the substrate/ice interface is developed, which in turn acts as a self-lubricant reducing material's ice adhesion strength. To put this idea into the test, we conducted extensive molecular dynamics (MD) simulations on ice supported by different types of substrates, such as graphite, boron nitride, and a cross-linked epoxy polymer. Our findings reveal that the ice structure becomes disordered near the interface for all substrates, with a more pronounced effect in the polymer substrate. The formation of QLL at the interface was quantified using metrics such as local density, order parameter, and hydrogen bonding. The polymer substrate showed a thicker QLL compared to the two flat surfaces, as this was verified by both the significant differences in the local water density profiles and the distribution of the employed order parameter. The latter ones were directly correlated to the development of hydrogen bonds between the interfacial water molecules and the polymer substrate's polar atoms, which was found to induce a more intense disruption of ice's crystal structure. Moreover, our analysis revealed that the polymer's oxygen atoms contribute more to hydrogen bonding with the water molecules than the nitrogen atoms, with hydroxyl oxygens (-OH) contributing more compared to the epoxy ones (-O-). The analysis related to the dynamics of the interfacial water molecules revealed a substantial reduction in mobility on the epoxy, exceeding the slowdown observed on boron nitride, with graphite demonstrating the least reduction in dynamic behavior among the substrates studied.
飞机表面结冰会带来重大的安全和性能风险，因此需要开发防止冰粘附的涂层。目前的工作重点是通过分子描述符来表征冰在各种基材上的界面特性。我们遵循先前在一些实验工作中提出的假设，即基材/冰界面处会形成无序的准液态水层（QLL），这反过来又作为一种自润滑剂降低材料的冰粘附强度。为了验证这一想法，我们对由不同类型的基材（如石墨、氮化硼和交联环氧聚合物）支撑的冰进行了广泛的分子动力学（MD）模拟。我们的研究结果表明，对于所有基材，冰结构在界面附近都会变得无序，在聚合物基材中这种影响更为明显。使用局部密度、序参量和氢键等指标对界面处QLL的形成进行了量化。与两个平面相比，聚合物基材显示出更厚的QLL，这一点通过局部水密度分布的显著差异和所采用序参量的分布得到了验证。后者与界面水分子和聚合物基材极性原子之间氢键的形成直接相关，发现这会导致冰晶体结构更强烈的破坏。此外，我们的分析表明，聚合物的氧原子与水分子形成氢键的贡献比氮原子更大，羟基氧（-OH）比环氧氧（-O-）的贡献更大。对界面水分子动力学的分析表明，环氧上的迁移率大幅降低，超过了氮化硼上观察到的减慢程度，石墨在所研究的基材中动态行为的降低最少。
