Nanoscale Characterization for Improving Turbulent Drag Reduction with Polymers Matthew W. Liberatore, Department of Chemical Engineering, Colorado School of Mines, Golden, CO 80401 Unentangled Solution Entangled Solution For unentangled xanthan solutions, the addition of salt results in a significant decrease in zero shear rate viscosity. The decrease in viscosity is observed for salt concentrations as low as 3 mM NaCl. However, for xanthan solutions above the critical concentration cD ≈ 2000 ppm, the addition of salt results in a measurable increase in viscosity. Turbulent drag reduction experiments using a homogeneous xanthan solution show reductions in drag by up to 37%. However, if an entangled stock solution (10,000 ppm or 1,000 ppm) of xanthan is diluted to the same concentration, the resulting drag reduction is improved by a factor of three. The improvement in drag reduction resulting from dilution of an entangled stock solution in diminished by the presence of salt.