Rheological behaviour of oil-filled polymer nanoparticles in aqueous dispersion

[Display omitted] •Aqueous SMI/oil dispersions behave as a viscoelastic medium at low stresses and become purely viscous at high stresses.•Presence of oil reduces viscosity and enhances viscoelastic properties of dispersion.•Overlap between rotational and oscillatory data for SMI/oil dispersions was found by considering the dynamic viscosity and shear viscosity as a function of shear stress.•Transition of viscosity with shear stress indicates yield point. Hybrid organic nanoparticles of poly(styrene-co-maleimide) with 70wt.-% incorporated palm oil (SMI/oil) were provided in aqueous dispersion for use in industrial coating processes. The rheological characteristics of dispersions with 65wt.-% and 35wt.-% solid content have been determined by creep, oscillatory and rotational testing under different shear stresses, shear rates, frequencies and temperatures. The effects of oil on viscoelastic properties have been demonstrated by comparative tests on a 35wt.-% pure SMI nanoparticle dispersion. The creep and strain recovery data show viscoelastic responses only for 65wt.-% SMI/oil dispersions at low stresses, as further detailed by the calculated Burger model parameters. The 65wt.-% SMI/oil dispersion at higher stresses and 35wt.-% SMI/oil dispersion over the full stress range become viscous. From strain sweep tests, the cross-over of G’ and G” demonstrates linear features at low strain and a transition into viscoelastic properties at high strain. The frequency sweep test indicates a linear solid-like behaviour with storage and loss modulus independent of frequencies at temperatures up to 70°C. From rotational tests, the sensitivity of shear-viscosity properties to concentration and temperature has been demonstrated. The oscillatory and rotational data can be fitted by the Cox-Merz rule using dynamic viscosity and shear viscosity as a function of frequency or shear stress, while a yield point has been detected as a function of shear stress for both 65 and 35wt.-% SMI/oil dispersions.