Sensitivity to shear stress of non-encapsulated thermochromic liquid crystal (TLC) particles for microfluidic applications

Tracer particles based on non-encapsulated thermochromic liquid crystals (TLCs) were recently introduced to probe the temperature and velocity field in microfluidic flows. In comparison with encapsulated TLC particles, which present an external polymeric coating, non-encapsulated particles provide a superior color response with larger signal-to-noise ratio. The absence of an external coating, however, leaves some open questions such as their reliability in flows with high shear rates, in which significant shear stress levels are applied on the particles. In this work, we address this specific issue through a series of systematic experiments under controlled flow and temperature conditions. The results showed no observable change in the color response up to a shear stress value of around 0.4 Pa. Consequently, particle-based temperature measurements are possible over the full shear stress range relevant for microfluidic applications. For larger shear stresses (up to 4 Pa), the color response remains reliable even though more and more particles start to be destroyed due to increased mechanical stresses.