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Visualization Of Nanoparticle Orientation Structures Inside Complex Fluids Using Polarized Light Imaging Technique

William Kai Alexander Worby, Yuto Yokoyama, Misa Kawaguchi, Hiroaki Kusuno, Yoshiyuki Tagawa

Tokyo University of Agriculture and Technology, Tokyo, Japan


The present paper reports on the effect of 3D-oriented particles on birefringence using the concept of 'rheooptics', a technique for identifying changes in the internal structure or flow dynamics of complex fluids from changes in optical anisotropy (birefringence). We used the photoelastic method, as a kind of polarized light imaging technique, to visualize the internal orientation structure induced by applying shear stress to cellulose nanocrystal (CNC) suspensions under shear flow. Two different rheometers (concentric cylinder and parallel plate-type) that can easily combine a birefringence measurement system were introduced to Transverse rotation Longitudinal rotation perform the shear flow induction, and the birefringence was measured and compared from vertical and horizontal directions for shear. The birefringence measurements from different directions provide an opportunity to investigate the effect of 3D-oriented CNCs on birefringence, which is a novelty of the present study. The measured birefringence was fitted with the empirical equation proposed in the previous study and followed the power law of applied shear rate with the same exponent, independent of the shear direction at the time of measurement This result suggests that there is a common physical background that gives birefringence a power law. This exponent was different from the values given in previous studies and is explained by differences in the particle interaction behaviour based on the concentration of suspensions and CNC length. Note that the proportionality coefficients differ by a factor of 10, clearly indicating differences due to the direction of birefringence measurement. These results indicate that birefringence due to transverse rotation of the CNC is more sensitive to shear stress than to longitudinal rotation.

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