A miniature capillary breakup extensional rheometer by electrostatically assisted generation of liquid filaments.

A micromachined chip capable of generating liquid microfilaments has been developed for a miniature version of the Capillary Breakup Extensional Rheometer (CaBER®). The proposed system is exceptionally simple and compact because liquid samples are actuated by voltages administered on-chip, which therefore requires only electrical connections (rather than a linear motor, an integral part of the CaBER®). Since chip features are photolithographically defined, the miniature rheometer can handle sub-microlitre samples. Following the CaBER®, we show that a commercial LED micrometer effectively measures diameters of filaments generated by the electrowetting-on-dielectric (EWOD) forces. Since negligible electric fields are sustained within the liquid far away from the measurement region, the applied EWOD voltage does not influence tested material properties. Through breakup experiments using a wide range of Newtonian and complex fluids (e.g., glycerol, xanthan gum, dilute polystyrene, and dilute solutions of various molecular weight polyethylene oxide) we demonstrate a versatile testing platform for scarce and precious samples such as biochemical fluids and novel materials. Measured Newtonian and complex dynamics agree well with published theories and experiments.