Abstract

The contact angle, as a vital measured parameter of wettability of material surface, has long been in dispute whether it is affected by gravity. Herein, we measured the advancing and receding contact angles on extremely low contact angle hysteresis surfaces under different gravities (1-8G) and found that both of them decrease with the increase of the gravity. The underlying mechanism is revealed to be the contact angle hysteresis and the deformation of the liquid-vapor interface away from the solid surface caused by gradient distribution of the hydrostatic pressure. The real contact angle is not affected by gravity and cannot measured by an optical method. The measured apparent contact angles are angles of inclination of the liquid-vapor interface away from the solid surface. Furthermore, a new equation is proposed based on the balance of forces acting on the three-phase contact region, which quantitatively reveals the relation of the apparent contact angle with the interfacial tensions and gravity. This finding can provide new horizons for solving the debate on whether gravity affects the contact angle and may be useful for the accurate measurement of the contact angle and the development of a new contact angle measurement system.

Highlights

  • Wetting is one of the basic characteristics of solid surfaces

  • The results show that the DMDCS was low contact angle hysteresis surface

  • We found that the contact angle was not affected by gravity, while the measured apparent contact angle was gravity-dependent

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Summary

Introduction

Wetting is one of the basic characteristics of solid surfaces. It is very important for processes like adhesion [1], selfcleaning [2], fluid drag reduction [3], heterogeneous nucleation [4], and the formation of coffee rings [5]. It has attracted immense interest in a large diversity of research fields ranging from physical, biological, and environmental sciences. The relationship between the wetting and gravity is one of them

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