A micro extensional filament rheometer enabled by EWOD

We present a miniature system for generating and measuring liquid microfilaments for capillary breakup rheometry. The key component is a chip that splits samples in open air, creating shear-free liquid threads that can be measured by optical micrometry. For testing polar samples, electrowetting-on-dielectric (EWOD) is used to induce spreading, which causes necking and capillary instability-driven breakup. Low-surface-tension samples spread spontaneously, and thus reach instability without EWOD. We use LED optical micrometry to measure inelastic and elastic microfilaments, and the results are consistent with capillary breakup theory and comparable to those obtained by established experimental methods.