Development of a MEMS based dynamic rheometer

Rheological methods that interrogate nanolitre scale volumes of fluids and solids have advanced considerably over the past decade, yet there remains a need for methods that probe the frequency-dependent complex rheological moduli through application of homogenous strain fields. Here we describe a Micro-Electro-Mechanical System (MEMS) based approach for the measurement of dynamic rheology of soft matter where oscillatory strain is produced in a sample sandwiched between an oscillating MEMS stage and a glass plate. The resulting stress-strain relationships are revealed by measurement and analysis of the stage motion. We present preliminary data on simple viscous fluids and on viscoelastic thin films. In this proof-of-principle device, we measure moduli in the range of 50 Pa to 10 kPa over a range of 3 rad s^-1 to 3000 rad s^-1 using less than 5 nL of sample material. The device's measurement window is limited primarily by our current ability to measure the motion of the stage. This device will provide a new way to characterize dynamic microrheology of an array of novel materials and will prove useful in a number of areas including biorheology, microfluidics and polymer thin films.