Determination of surface tension coefficient of liquids by diffraction of light on capillary waves

Abstract

This paper describes a simple technique for determining the coefficient of the surface tension of liquids, based on laser light diffraction on capillary waves. Capillary waves of given frequency are created by an exciter needle acting on the surface of liquid and represent a reflective diffraction grating, the constant of which (the wavelength of capillary waves) can be determined based on a known incidence angle of light (grazing angle). We obtain the coefficient of the surface tension of liquids by applying the dispersion relation for capillary waves and analyze the difficulties that arise when setting up and conducting the experiment in detail.

Spreading of macromolecules at the air/water interface

“…115 The use of light-diffraction from the capillary waves of liquid interfaces has also been reported. 117,118 In this thesis work, however, only the Wilhelmy method is used, in which the exerted force of a liquid wetted plate is measured. A schematic representation of a wetted plate is given in figure 8.…”

Universal Stokes’s nanomechanical viscometer

“…Although, all-optical excitation of fluid interface using radiation-pressure and optical detection of surface dynamics is attractive, these approaches are limited to semi-transparent samples, because otherwise the laser absorption essentially induces thermal effects which compete with viscous damping. Several techniques have been used to study surface waves on liquids such as photon correlation spectroscopy (PCS) 13 of thermal fluctuations, light scattering 14 , 15 , diffraction from dynamic grating on fluid surface 16 – 18 , imaging 19 – 21 , profilometry 22 , 23 and laser interferometry 24 , 25 . In photon-correlation spectroscopy technique, although thermal fluctuation can excite surface waves on most fluids, measuring attenuation using line broadening of the scattered laser light requires integration time of about 20 s and therefore, cannot measure nanomechanical deformation in real-time.…”

The study of liquid surface waves with a smartphone camera and an image recognition algorithm

“…The data give the dispersion relation of surface waves and provide a method for determining the surface tension of fluids. To measure the wavelength, noncontact techniques based on laser interferometry [7] and laser diffraction [8] are proposed, which are more complicated approaches. In this paper, we introduce a simple experimental setup.…”

“…In this experiment we provide a path for participants to understand image recognition techniques. Compared with the approaches above [7,8], ours is a simple and portable setup that is suitable not only for classrooms, but also for amusement parks and science museums. Entertaining and educational experiments that can be well conducted [9] help increase interest and motivation for people to understand scientific knowledge.…”