A bottom-up framework for the nanoscale origins of ice formation and adhesion on structured surfaces

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Icing is frequently encountered in nature and has adverse consequences on many human activities. Of particular importance is ice formation on rough surfaces, which are also chemically inhomogeneous. Surface roughness and composition drastically influence icing behavior, and consequently, ice adhesion, which is important for ice removal. By developing a better understanding of ice formation on realistic surfaces, appropriate steps can be taken to avert icing in situations where lives are threatened or when machines encounter trouble operating in freezing temperatures. The main goal of the work is to produce science-based guidelines for optimal anti-icing performance (maximum freezing delays and minimal ice adhesion). Using spectroscopic tools in conjunction with liquid-cell scanning transmission electron microscopy (STEM) and in-situ cryo-cooling, the research examines icing on surfaces having nanoscale roughness and compositions from wettable to non-wettable. The methodology employs graphene liquid cells (GLCs) with encapsulated nanoparticles of varying wettabilities and sizes. The GLCs allow electron microscope (nm-scale resolution) dynamic observations of encapsulated nanoparticle suspensions in water, and with precise temperature control, they become vacuum-tight vessels for interrogating icing kinetics in real time. Ice formation is controlled by modulating the GLC sample temperature under various cooling scenarios. Parallel in-situ nanoscale spectroscopic methods quantify the ice/water mass ratio and structure around the nanoparticles during and after freezing, as a function of particle size, wettability and confinement in the atomically-thin-walled graphene cell. The macroscopic experiments, on the other hand, use surfaces with chemistry and characteristic length texture similar to the nanoscopic experiments, to determine macro freezing delays and ice adhesion strength. By correlating the macroscale ice properties with the nanoscale kinetic parameters, the project produces guidelines for optimal anti-icing performance or easy ice removal. The research, by generating high-quality experimental data for a spatial regime of multiphase transport that has been inaccessible by existing instrumentation, also opens new horizons for validating and advancing models simulating nanometer-scale multiphase systems.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.