Spontaneous Takeoff of Single Sulfur Nanoparticles during Sublimation Studied by Dark-Field Microscopy

Abstract

The Leidenfrost effect describes a fascinating phenomenon in which a liquid droplet, when deposited onto a very hot substrate, will levitate on its own vapor layer and undergo frictionless movements. Driven by the significant implications for heat transfer engineering and drag reduction, intensive efforts have been made to understand, manipulate, and utilize the Leidenfrost effect on macrosized objects with a typical size of millimeters. The Leidenfrost effect of nanosized objects, however, remains unexplored. Herein, we report on an unprecedented Leidenfrost effect of single nanosized sulfur particles at room temperature. It was discovered when advanced dark-field optical microscopy was employed to monitor the dynamic sublimation process of single sulfur nanoparticles sitting on a flat substrate. Despite the phenomenological similarity, including the vapor-cushion-induced levitation and the extended lifetime, the Leidenfrost effect at the nanoscale exhibited two extraordinary features that were obviously distinct from its macroscopic counterpart. First, there was a critical size below which single sulfur nanoparticles began to levitate. Second, levitation occurred in the absence of the temperature difference between the nanoparticle and the substrate, which was barely possible for macroscopic objects and underscored the value of bridging the gap connecting the Leidenfrost effect and nanoscience. The sublimation-triggered spontaneous takeoff of single sulfur nanoparticles shed new light on its further applications, such as nanoflight.

In Situ Multicolor Imaging of Photocatalytic Degradation Process of Permanganate on Single Bismuth-Based Metal–Organic Frameworks

“…Dark-field optical microscopy (DFM) obliquely illuminates particles to generate elastic scattering of light, which prevents the incident light from entering the objective, resulting in a dark background . DFM allows for acquiring high-quality color images with significant contrast and excellent sensitivity, making it suitable as a versatile and powerful tool for real-time monitoring of various chemical reactions at a single-particle level. − For a long time, DFM is mainly limited to chemically imaging single plasmonic nanoparticles (Au, Ag, and doped semiconductor nanomaterials) due to their strong light-scattering capacity . Recently, we have demonstrated that the scattering light is sensitive to the alteration in the optical absorption and mass of single MOFs, realizing single-particle imaging of iodine adsorption and thermal dehydration processes on MOFs. , …”