Rheofluidics: frequency-dependent rheology of single drops

We present Rheofluidics, a microfluidic technique that measures the frequency-dependent rheology of individual micron-scale objects. We apply oscillatory hydrodynamic stresses by flowing them through channels with modulated constrictions, and measure their deformation. Unlike bulk rheology, which measures collective properties, Rheofluidics provides heretofore unattainable measurements of individual particles. We apply Rheofluidics to discover frequency-dependent surface tension of surfactants, very high-frequency viscoelasticity of microgels and unexpected frequency-dependent bending modulus of vesicles.