Microviscoelasticity of adhesive hard sphere dispersions:Tracer particle microrheology of aqueous Pluronic L64 solutions

摘要

DWS-based tracer particle microrheology is demonstrated to be a useful way to study the dynamicsof aqueous Pluronic L64 solutions, which is viewed as a model adhesive hard sphere (AHS) system.The short-time dynamics of aqueous Pluronic L64 solutions indicate a purely hydrodynamic highfrequency microviscosity as predicted by Batchelor for colloidal dispersions. The evolution of themicellar dynamics reveals a zero shear microviscosity in good agreement with steady shear viscositymeasurements. As the temperature is increased, the dynamics become dominated by an apparentattractive intermicellar potential observed in microscopic creep measurements. While Pluronic L64solutions have been reported to form a percolated micellar network, DWS-basedmicroviscoelasticity measurements do not detect the previously observed G'～G"～ωΔscalingexpected for a static percolated network at low frequencies. This most likely owes to the fact thattracer particle microrheology is dominated by local Pluronic L64 micelle dynamics in the nearsphere region and not the bulk mechanical properties as measured by traditional rheometry. Thesensitivity of tracer particle microrheological measurements to the true dynamic nature of thepercolated network in weak physical gels highlights the distinct differences between these micro-and macrorheology measurement techniques. Such discrepancies should be most evident in systemsthat are dominated by association processes such as those occurring in AHS solutions or polymersolutions approaching a phase boundary. Despite this, the AHS potential is qualitatively consistentwith the results found here.