Rheological Characterization of a Waterborne Organic Nanoparticle Dispersion

Organic nanoparticles of poly(styrene-co-maleimide) or SMI were synthesized in aqueous dispersion with a maximum concentration of 35 wt.% and are favorably applied in industrial coating processes. In order to evaluate the further processability and flow behavior of these nanoparticle dispersions, general rheological characterization under creep, oscillatory and rotational testing was done by applying various shear stresses, shear rates and frequencies on an air-bearing cylindrical rheometer. Creep tests at different stresses show that the nanoparticle dispersions behave like a viscous material. The crossover of G’ and G” according to oscillatory experiments also demonstrates a transition to viscoelastic behavior at high frequency. The sensitivity of shear-viscosity behavior to concentration and temperature of the dispersions has been evaluated. In parallel, the influences of gap size, repeatability and water evaporation have been statistically evaluated and could be successfully controlled. By comparing oscillatory and rotational rheometry data, flow curves under low shear rates were reconstructed.