A Self-Build Apparatus for Oscillatory Flow Birefringence Measurements in a Co-Cylindrical Geometry

Abstract

We developed a high-sensitive apparatus for oscillatory flow birefringence measurement in a co-cylindrical geometry. The apparatus was comprised of a conventional rheometer, an Argon ion laser, and a lock-in amplifier. The laser was irradiated to samples under sinusoidal strains, and transmitted light intensities were analyzed using the lock-in amplifier to evaluate flow birefringence. TTL signals, which were transformed from sinusoidal strains using a comparator, were used as reference signals for lock-on detection at low frequencies. First, phase shifts between the true strain and TTL reference signal generated by the comparator were calibrated. Next, reliability of the apparatus was assessed using a wormlike micellar solution, whose flow birefringence behavior are well known. Finally, sensitivity of the birefringence measurement was checked using a low birefringent cellulose nanofiber (CNF) dispersion. Flow birefringence behavior of the CNF dispersion became measurable thanks to a long optical pass length of the geometry. The apparatus will be a strong tool to reveal dynamics of low birefringent solutions.