Hydrodynamic instability and phase separation in nanometric thin thilms of melted metalic alloys

DIEZ, J. A.; GONZÁLEZ, A. G.; KONDIC, LOU

Paraná

Congreso; Fluidos 2021 - XVI Reunión sobre Recientes Avances en Fı́sica de Fluidos y sus Aplicaciones; 2021

We consider the coupled process of phase separation and dewetting of metal alloys of nanoscalethickness deposited on solid substrates. The experimental setup used to study these systemsinvolves applying nanosecond laser pulses that melt the Ag 40 Ni 60 alloy films on silicon wafers(Langmuir 37, 2575 (2021)). The theoretical model considers a Cahn?Hilliard formulation in theform of gradient dynamics used to describe spinodal decomposition, coupled with asymptoticallyconsistent longwave based description of dewetting that occurs due to destabilizing interactionbetween the alloy and the substrate, modeled by using the disjoining pressure approach. Carefulmodeling, combined with linear stability analysis and fully nonlinear simulations, leads to resultsconsistent with the experiments. In particular, we find that two instability mechanisms occurconcurrently, with the phase separation evolving faster and on shorter spatial scales than thehydrodynamic instability that leads to formation of drops. The modeling results show a stronginfluence of the temperature dependence of relevant material properties, implying that such adependence is crucial to the understanding of the experimental findings. The agreement betweentheory and experiment suggests the utility of the proposed theoretical approach in helping todevelop further experiments directed toward formation of metallic alloy nanoparticles of desiredproperties. We explore the possible coupling of modes due to a dependence of the disjoiningpressure on surface and/or bulk concentrations, as well as eventual Marangoni effects.