Dynamics of Nanoparticle-Assisted Melting and Recrystallization of Water Ice

当你把温度提高到0摄氏度或32华氏度时，冰就会融化。熔化似乎是一个简单的过程，但在分子水平上要复杂得多。熔化过程从表面开始。原因是，位于表面或与另一种材料交界处的水分子，与位于固体更深处的水分子相比，被较少的邻近水分子包围。事实上，只有这个数字的一半。邻居越少，水分子的运动就越自由。其结果是，即使在低于熔化温度的温度下，也会在界面上形成预熔的液态层。在化学系大分子、超分子和纳米化学项目的支持下，印第安纳大学的Dragnea和Ye教授正在使用复杂的显微镜方法研究冰嵌入的单个金纳米颗粒周围预熔液层的形成。他们的工作可能对理解环境和地球物理背景下的冰融化和重结晶具有广泛的影响，例如雪地的融化和冻土的融化，所获得的见解可能有助于推动新型粘合剂和润滑剂的开发。该项目为研究生和本科生提供了开发复杂实验方法的培训机会。此外，与印第安纳大学商学院的一项创业合作正在向未来的科学家和未来的商业专业人士介绍将发明转化为商业化产品的过程。Dragnea和Ye教授与他们的学生一起工作，使用激光来激发单个金纳米颗粒。这些纳米颗粒由叶氏集团以精确的尺寸生长，并被有机层包围，然后被封装在冰中。Dragnea小组使用光学和电子显微镜观察到了预熔液层的形成。光热显微镜可以观察到纳米粒子表面附近冰的融化和重结晶，而界面形态则通过石墨烯液体细胞透射电子显微镜观察。预熔层形成的温度取决于水分子和纳米颗粒表面之间的化学作用，以及颗粒的大小和曲率。通过研究单个纳米颗粒，研究团队可以绕过研究大颗粒集合时产生的问题，在大颗粒集合中，不同大小的颗粒表现出不同的预熔化行为。实验结果得到了数值模拟的补充，以确定界面层的动力学参数和物理性质。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Ice melts when you raise the temperature to 0C, or 32F. Melting seems like a simple process, but at the molecular level it is much more complicated. The melting process starts at the surface. The reason is that a water molecule sitting at the surface, or at the interface with another material, is surrounded by fewer neighboring water molecules than one located deeper into the solid. Half as many, in fact. With fewer neighbors, water molecules move more freely. The result is the formation of a pre-melted liquid layer at the interface, even at temperatures colder than the melting temperature. With support from the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professors Dragnea and Ye at Indiana University are using sophisticated microscopy methods to study the formation of the pre-melted liquid layer around individual gold nanoparticles embedded by ice. Their work could have broad implications for understanding ice melting and recrystallization in environmental and geophysical contexts, such as the melting of snow fields and the thawing of frozen soils, and insights gained could help advance the development of new adhesives and lubricants. The project provides training opportunities for graduate and undergraduate students in the development of complex experimental methods. In addition, an entrepreneurial collaboration with the Indiana University School of Business is introducing future scientists and future business professionals to the process of translating inventions into commercialized products.Working alongside their students, Professors Dragnea and Ye use laser light to excite individual gold nanoparticles. The nanoparticles are grown by the Ye group with precise sizes and surrounded by an organic layer and then encapsulated in ice. The formation of pre-melted liquid layer is observed by the Dragnea group using optical and electron microscopies. Photothermal microscopy provides insight into melting and recrystallization of the ice near the nanoparticle surface, while interfacial morphology is observed by graphene liquid cell transmission electron microscopy. The temperature at which the pre-melted layer forms depends on the chemical interaction between water molecules and the nanoparticle surface, as well as the particle size and curvature. By studying single nanoparticles, the research team can circumvent problems arising from the study of large collections of particles, where particles of different sizes exhibit different pre-melting behaviors. Experimental results are complemented by numerical simulations to determine kinetic parameters and physical properties of the interfacial layer.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.