Abstract
Modern methods of controlling the shape of interfacial surfaces of miscible and immiscible liquids, as well as technologies based on them, adaptive liquid optics, or the so-called free-form optics, require a deep understanding of the processes of heat and mass transfer occurring at the interface. These processes have a significant effect on the shape of the surface and the rate of its transition to a stable state, which is the determining criterion for accommodating the optical characteristics of liquid-layer optics. The aim of this work is to study the main modes of thermocapillary convection in a horizontal system of two immiscible liquids. The reason for the occurrence of heat and mass transfer in the system under study was the local heating of the interface with the help of laser radiation. The technique for obtaining information about the change in the curvature of the layer surface as an indicator of the hydrodynamic stability of the system is based on measuring the diameter of the interference pattern formed on a remote screen by a laser beam reflected from the deformed surface of the liquid. Using this method, it was found that one of the systems under consideration (benzyl alcohol — polymethylsiloxane) is characterized by the appearance of hydrodynamic instability of an oscillatory nature, which manifests itself in a change in the shape of both the interface between the two liquids and the free boundary. The distinctive features of the evolution of the detected instability are shown, and an assumption is made about the influence of microbubble clusters, revealed by the method of optical microscopy, as the cause of the onset and damping of oscillations. It is assumed that the movement of bubble clusters by means of thermocapillary flows and capillary drift contributes to the formation of a local difference in interfacial tension, leading to destabilization of the stable deformation of the layer and the transition of the system to a mode of oscillatory instability. The decay times and periods of oscillations are determined depending on the thickness of the upper layer.