Measurement of high viscosity with laser induced surface deformation technique

Abstract

A technique for viscosity measurement was developed based on the principle of laser-induced surface deformation. Light incident into liquids increases its momentum due to the difference in refractive index and gives the surface an upward force as a reaction. The plane surface thus swells up and deforms, and the shape is determined so that the force is balanced with the surface tension and the gravity. On sudden laser irradiation, the deformation inevitably accompanies a viscous flow and exhibits a relaxational behavior with a delay time, which gives the viscosity. Theoretical prediction of the step-response function was given that takes surface tension waves excited by the laser into consideration. Nd–yttritium–aluminum–garnet laser with 0.6W output was focused to ∼200μm beam waist and used for the pumping. The deformation process was observed sensitively with another probe laser illuminating the activated area. This system was tested with the standard liquids for viscosity ranging from 1 to 106cSt. The results demonstrated the validity of this technique, though a correction for the inertia effect was needed in the range lower than 10cSt. Further, effect of the thermal expansion by a slight optical absorption was discussed. This technique is especially useful at high viscosities since the measurement takes only a few seconds even in the specimen with 106cSt. Besides the rapidity, it has a great advantage of a noncontact feature and is appropriate for measuring the liquids that strongly dislike contamination. It has also potential applications in industries, measurement of liquids isolated in a production line, for instance.

Light-induced deformation and instability of a liquid interface. II. Dynamics

“…Extending the results of ref. [10] to the case of liquid-liquid interfaces and to the Bo 1 regime, we showed that, in the Bo 1…”

“…The key point here is the contactless property of the method which allows for in situ measurements and prevents mechanical contact with fluid surfaces as well as possible chemical contamination by these mechanical disturbances. This dynamical approach was further extended to the difficult problem of the quantitative measurements of high viscosity systems [10]. The advantage here is the rapidity of measurements (typically a few seconds) associated to the fact that the viscous motion of the fluid is limited to the microscopic volume excited by the laser beam.…”

Laser microfluidics: fluid actuation by light

“…In a second work [47], they focused their attention on the difficult case of ultra low interfacial tension, for which most of classical techniques fail. Finally, they showed the pertinence of radiation pressure to measure shear viscosities [48]. The characterization of the mechanical properties of lipidic membranes is also of fundamental interest in biophysics.…”

Noncontact Measurement of Viscosity of B2O3 Melt Using Electric-field Tweezers

“…oscilloscope. Note that the samples used in this study had a nearly spherical curvature, making it difficult to detect the reflected light using the optical lever technique 6,8,9) to measure the surface gradient. In this study, therefore, the laser was reflected on the deformed portion of the sample surface and was detected by a photodiode.…”