Kant Pallav, Koldeweij Robin B J, Harth Kirsten, van Limbeek Michiel A J, Lohse Detlef
Physics of Fluids Group, Max Planck Center Twente for Complex Fluid Dynamics and J. M. Burgers Centre for Fluid Mechanics, MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands;
Physics of Fluids Group, Max Planck Center Twente for Complex Fluid Dynamics and J. M. Burgers Centre for Fluid Mechanics, MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands.
Proc Natl Acad Sci U S A. 2020 Feb 11;117(6):2788-2794. doi: 10.1073/pnas.1912406117. Epub 2020 Jan 24.
Freezing or solidification of impacting droplets is omnipresent in nature and technology, be it a rain droplet falling on a supercooled surface; in inkjet printing, where often molten wax is used; in additive manufacturing or metal-production processes; or in extreme ultraviolet lithography (EUV) for the chip production, where molten tin is used to generate the EUV radiation. For many of these industrial applications, a detailed understanding of the solidification process is essential. Here, by adopting an optical technique in the context of freezing-namely, total-internal reflection (TIR)-we elucidate the freezing kinetics during the solidification of a droplet while it impacts on an undercooled surface. We show that at sufficiently high undercooling, a peculiar freezing morphology exists that involves sequential advection of frozen fronts from the center of the droplet to its boundaries. This phenomenon is examined by combining elements of classical nucleation theory to the large-scale hydrodynamics on the droplet scale, bringing together two subfields which traditionally have been quite separated. Furthermore, we report a self-peeling phenomenon of a frozen splat that is driven by the existence of a transient crystalline state during solidification.
冲击液滴的冻结或凝固在自然和技术领域无处不在，比如雨滴落在过冷表面上；在喷墨打印中，常使用熔化的蜡；在增材制造或金属生产过程中；或者在用于芯片生产的极紫外光刻（EUV）中，使用熔化的锡来产生EUV辐射。对于许多此类工业应用而言，详细了解凝固过程至关重要。在此，通过在冻结背景下采用一种光学技术——即全内反射（TIR），我们阐明了液滴冲击过冷表面时凝固过程中的冻结动力学。我们表明，在足够高的过冷度下，存在一种特殊的冻结形态，它涉及冻结前沿从液滴中心到其边界的顺序平流。通过将经典成核理论的要素与液滴尺度上的大规模流体动力学相结合来研究这一现象，将两个传统上相当分离的子领域结合在一起。此外，我们报告了一种冻结薄片的自剥离现象，它是由凝固过程中瞬态晶体状态的存在所驱动的。
