Dynamic Optical Studies of Transport Phenomena Associated with Melting and Recrystallization at the Nanoparticle-Ice Interface

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With support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program in the Division of Chemistry, Professor Bogdan Dragnea at Indiana University is utilizing sophisticated microscopies to study how nanoparticles affect ice melting. It is well-know that ice melts to form water when the temperature reaches 32 degrees Fahrenheit, or 0 degrees Celsius. However, this is not always the case. Nanoparticles, which are about a million times smaller than the period at the end of this sentence, can change this transition temperature. When embedded in ice, a thin layer often forms near the nanoparticle surface that can melt below normal temperatures. Working with his students, Professor Dragnea uses a photothermal microscopy technique to observe the melting of this thin ice layer when the nanoparticle is rapidly heated by a laser. Their discoveries could have implications for understanding a variety of environmental processes such as ice crystal formation in the atmosphere, as well as provide ways of controlling friction and adhesion on icy surfaces. The project is also providing research opportunities for graduate and undergraduate students from diverse backgrounds. In addition, through collaboration with the Indiana University Research and Technology Corporation (IURTC), Professor Dragnea is introducing his students to entrepreneurial concepts as they translate the project's instrumentation and scientific knowledge into useable technologies. Professor Dragnea is developing photothermal microscopy methods to obtain the transport and thermodynamic properties of the interfacial quasi-liquid layer (QLL) that separates the solid surface of a nanoparticle from bulk ice. Single nanoparticles with well-defined surface chemistries and geometries are embedded in a film of polycrystalline ice. The nanoparticle is then heated by laser excitation, raising the temperature of the surrounding solid. The formation of the QLL is detected by measuring the light scattered by the nanoparticle at various temperatures. The measurement is facilitated by modulation of the interfacial liquid thickness through repeated absorption of laser pulses by the nanoparticle. In addition to characterizing the convex surfaces of spherical nanoparticles, the formation of the QLL near concave surfaces of shape-controlled nanoparticles is also studied. By comparing optical and thermal simulations to experimental observations, transport and thermodynamic parameters are extracted. Experiments performed on individual particles alleviate challenges associated with impurities, defects, and particle-to-particle variations that reduce accuracy.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.