Relation between quadrupole ultrasonic resonance and shear viscoelasticity of polymer droplets with different glass transition temperatures

Abstract

When observing the ultrasonic signal transmitted through a suspension of particles dispersed in a liquid, a peak is observed in the frequency spectrum of the attenuation coefficient of the ultrasonic energy. This peak mainly reflects shear elasticity, even though longitudinal ultrasound is used. Hence, the shear modulus of a single particle dispersed in a liquid can be obtained in a non-contact manner. In this study, we used ultrasound to analyze the process of polymer particle formation from an oil-in-water emulsion, in which a polymer solution containing an organic solvent is used as the oil phase, and the organic solvent is evaporated in water. Furthermore, the liquid-to-solid transition was quantified for microparticles consisting of various polymeric materials (liquid, rubber, and glass), and the relationship between the glass transition temperature, peak behavior of ultrasonic attenuation coefficient, and shear modulus was clarified.