Influence of concentration and flow rate on the birefringence of graphene oxide liquid crystals in microchannels

This study presents a hydrodynamic approach to tuning the birefringence of graphene oxide liquid crystals (GO-LCs) in microfluidic environments. Unlike traditional methods that rely on electric or magnetic fields, often requiring bulky and complex setups, this method leverages fluid dynamics to control the alignment of GO flakes in aqueous dispersions. By systematically varying concentration and flow rate, we demonstrate that nematic phase formation and birefringence in GO-LCs can be precisely modulated. Experimental measurements under transmitted light reveal that increasing the flow rate to 0.9 mL/h results in a 54.55% enhancement in birefringence at a fixed concentration of 0.22% vol. Similarly, increasing the concentration from 0.17% vol to 0.22% vol yields a 42.59% average increase in birefringence across all flow rates. These results highlight the strong dependence of optical anisotropy on microchannel flow conditions and GO loading. Importantly, this hydrodynamic tuning method is well-suited for applications where electric or magnetic fields may interfere with sensitive biological samples or are otherwise impractical. Furthermore, it enables more uniform particle alignment and, in cases requiring external fields, reduces the necessary field strength, thus enhancing overall electro-optical performance. This work provides a foundation for the development of efficient, field-free tuning strategies in next-generation optical, biosensing, and lab-on-a-chip systems.