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Thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) particles of a nearlyconstant swelling ratio and with polydispersity indices (PDIs) varying over awide range (7.4% - 48.9%) are synthesized to study the effects ofpolydispersity on the dynamics of suspensions of soft PNIPAM colloidalparticles. The PNIPAM particles are characterized using dynamic lightscattering (DLS) and scanning electron microscopy (SEM). The zero shearviscosity ($\eta_{0}$) data of these colloidal suspensions, estimated fromrheometric experiments as a function of the effective volume fraction$\phi_{eff}$ of the suspensions, increases with increase in $\phi_{eff}$ andshows a dramatic increase at $\phi_{eff}=\phi_{0}$. The data for $\eta_{0}$ asa function of $\phi_{eff}$ fits well to the Vogel-Fulcher-Tammann (VFT)equation. It is observed that increasing PDIs results in increasingly fragilesupercooled liquid-like behavior, with the parameter $\phi_{0}$, extracted fromthe fits to the VFT equation, shifting towards higher $\phi_{eff}$. Theobserved increase in fragility is attributed to the prevalence of dynamicalheterogeneities (DHs) in these polydisperse suspensions, while the simultaneousshift in $\phi_{0}$ is ascribed to the decoupling of the dynamics of thesmallest and largest particles. Finally, it is observed that the intrinsicnonlinearity of these suspensions, estimated at the third harmonic near$\phi_{0}$ in Fourier transform oscillatory rheological experiments, increaseswith increase in PDIs. Our results are in agreement with theoreticalpredictions and simulation results for polydisperse hard sphere colloidalglasses and clearly demonstrate that jammed suspensions of polydispersecolloidal particles can be effectively fluidized with increasing PDIs.

Effects of polydispersity on the glass transition dynamics of aqueous suspensions of soft spherical colloidal particles