PARTICLE TRACKING MICRORHEOLOGY OF COMPLEX FLUIDS

We present a new method for measuring the linear viscoelastic shear mo duli of complex fluids. Using photodiode detection of laser light scat tered from a thermally excited colloidal probe sphere, we track its tr ajectory and extract the moduli using a frequency-dependent Stokes-Ein stein equation. Spectra obtained for polyethylene oxide in water are i n excellent agreement with those found mechanically and using diffusin g wave spectroscopy. Since only minute sample volumes are required, th is method is well suited for biomaterials of high purity, as we demons trate with a concentrated DNA solution.