Application of a microrheology technique to measure the viscosity of disodium cromoglycate liquid crystal

ABSTRACT

Although the science of rheology is well established, some important challenges still persist to measure the viscoelastic properties of complex fluids, such as biological solutions and liquid crystals (LC). In this work, we present a method, based on the calculation of the step length of Brownian particles, to measure the effective local viscosity sensed by microscopic objects in the LC host. This approach allowed us to quantify the anisotropy of the viscosity, and it could also be extended to measure the local viscosity in other nonhomogeneous media. We also present a new guided light dark-field microscopy technique that was used to track particles during our experiments.

KEYWORDS:

• Brownian motion
• dark-field microscopy
• DSCG
• liquid crystal
• viscosity

Acknowledgments

The authors acknowledge the financial support of the Canada Foundation for Innovation (CFI), the Natural Sciences and Engineering Research Council of Canada (NSERC), and CREATE. T.G. thanks Canada Research Chair in Liquid Crystals and Behavioral Biophotonics and Manning Innovation price for financial support. We are grateful to G. Paradis, K. Allahverdyan and Dr. A. Tork (from LensVector and TLCL Optical Research Inc.) for their help during our experiments, to the group of H.C. Berg for bacterial strains, and to Remy Colin for sharing with us his tracking algorithm.