Cover titleIncreased blood viscosity in patients with small artery occlusion Key wordsblood viscosity, ischemic stroke, small artery occlusion, pathogenesis, rheology, dehydration 2 Abstract Background and Purpose: High blood viscosity causes blood stagnation and subsequent

We developed a technique of picking up the liquid surface in a noncontact manner by a cw-laser radiation. The momentum change of light at the laser transmission through the air-liquid interface appears as the radiation pressure, which deforms the liquid surface into the shape determined by the balance between the Laplace force of the curved surface and the radiation pressure. The displacement of the liquid surface is inversely proportional to the surface tension, which was measured by an optical probe. The dynamic response of the liquid surface deformation was theoretically derived under the periodical modulation of the radiation pressure. The experimentally observed spectra were in good agreement with the theory giving the dynamic properties of the liquid surface. The technique of the laser induced surface deformation has potential as a measurement tool of the surface dynamic properties, such as the time-dependent surface tension and surface viscoelasticity.

The liquid surface or interface is deformed slightly by a laser beam passing through it. Based on this principle, a method to measure the liquid-liquid interfacial tension is developed. The interfacial tension is determined from the deformation, of which the displacement is measured with another probe laser in a noncontact manner. The measurements were available in two different senses: the constant displacement under continuous laser irradiation gives the static value, and the frequency response spectrum of the displacement under modulated excitation gives the dynamic value. To demonstrate the usefulness of this method, a series of experiments were conducted in the interface between heptane and water containing aerosol OT as a surfactant. The interfacial tension was controlled by the concentration of added NaCl, and measurements were made over the range from 1 microN/m to 100 mN/m of the tension. The results were in good agreement with the previous works. This method would be a new tool for the studies of various interfacial phenomena.

We have developed a simple system for viscosity measurement in the range of 10-3 to 101 Pa·s. An aluminum sphere revolves in a sample cell under a rotating external magnetic field, and the rotational speed of the sphere gives the sample viscosity. Low viscosities can be measured by using a micro-probe sphere, since the viscous torque applied to the sphere overcomes the frictional force at a sufficiently small sphere radius. The system is free from contamination and can be easily applied to medical and biological studies.

We performed a dynamic evanescent light-scattering experiment to observe the Brownian motion of the sphere particles near the solid-liquid interface. An evanescent wave generated in a colloidal solution picks up information on the dynamics close to the solid interface within the submicrometer penetration depth. Measurement was made for various diameters of polystyrene spheres in a wide wave-number range of light scattering. The autocorrelation function obtained for particles smaller than the penetration length shows nonexponential behavior, which is successfully described by considering the complex scattering wave number brought about by the finite interaction region between the light and the sphere. The diffusion constant near the interface is smaller than that for free diffusion in a bulk solution, suggesting the suppression of Brownian motion due to the hydrodynamic interaction between the sphere and the solid wall. Furthermore, the Brownian motion was found to be anisotropic with respect to the directions parallel and perpendicular to the interface. The two different diffusion constants can be obtained uniquely by observation over a wide range of wave number. The diffusion constants thus obtained agree well with the values derived from hydrodynamic theory.

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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.

The authors have developed a novel technique to measure the surface properties of soft condensed matters in a noncontact manner. In this method, the Maxwell stress applied by a needle electrode deforms the surface. The magnitude of the displacement is determined by the surface tension as the restoring force, while its dynamic response is determined by the sample viscosity. The surface tension was measured for the aqueous solutions of the surfactant sodium dodecyl sulfate at various concentrations and the result shows good agreement with the conventional method. Further, the viscosity measurement was also carried out in the range of 0.1–103Pas.