Magnetic-Field-Controlled Photoinduced Thermocapillary Deformation of Magnetic Fluid Surface
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etic-Field-Controlled Photoinduced Thermocapillary Deformation of Magnetic Fluid Surface Yu. I. Dikanskiia, A. R. Zakinyana, *, V. D. Mkrtchyana, and G. Kh. Usmanova aNorth
Caucasus Federal University, Stavropol, 355017 Russia *e-mail: [email protected]
Received January 24, 2020; revised March 19, 2020; accepted March 25, 2020
Abstract—The influence of a magnetic field on the features of photoinduced thermocapillary deformation of the free surface of a magnetic fluid layer is considered for the first time. Deformation occurs as a result of local heating of the surface under the action of an incident laser beam and manifests itself as a curvature of the fluid surface profile. The laser beam reflected from the deformed surface exhibits a nonuniform spatial distribution of the radiation intensity in the form of concentric rings. An external magnetic field has an addition effect on the shape of the free surface of the magnetic fluid, thereby making it possible to control the photoinduced thermocapillary deformation. The geometric characteristics and time evolution of the interference pattern of the thermocapillary response are experimentally studied as depending on the strength and orientation of the magnetic field. DOI: 10.1134/S1061933X2005004X
INTRODUCTION Nonuniform heating of a free surface of a thin fluid layer is accompanied by its deformation [1–4]. One of the reasons for this effect is the temperature dependence of the surface tension coefficient. For example, the local heating from above of a thin fluid layer, which is located on a solid horizontal substrate and has a free upper surface, gives rise to the development of a surface tension gradient on the surface. In this case, tangential stresses directed radially from the heating point induce a fluid flow, which is directed toward the regions with lower temperatures. Due to viscous friction, the moving surface layers of the fluid entail its bulk, thus inducing the development of thermocapillary convection in the fluid layer. The local convective flows lead to changes in the profile of the free surface of the fluid. Such local heating can be realized by irradiating the surface of a fluid layer with a laser [5–8]. In this case, being projected onto a screen, a laser beam reflected from the deformed surface exhibits a socalled thermocapillary response, the geometry of which allows us to judge the features of the thermocapillary deformation of the fluid surface layer. The phenomenon under consideration, which is also known as a thermo-optical mirror, is employed in a number of methods used to measure the viscosity of fluids, the thermal conductivity and thermal diffusivity of substrate materials, the concentrations of surfactants in fluids, etc. [9, 10]. It should be noted that the elaboration of efficient thermo-optical media is currently of a considerable
interest in the context of basic researches and applied developments. In this regard, attention is focused on the use of nanomaterials in such studies, in which nanoparticles or clusters play a significa
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