Dynamics of Nanoparticle-Assisted Melting and Recrystallization of Water Ice

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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.