Cluster formation during aging of colloid-polymer dispersions and re-entrant rheological behavior at interfaces and the microscale
July 21-24, 2019
We report the dynamics of aqueous dispersions of the disk-shaped colloidal clay laponite® with poly(ethylene oxide) (PEO) chains of moderate molecular weight, explored via angle-dependent dynamic light scattering (DLS), bulk rheology, passive microrheology, and interfacial rheology. The PEO chains adsorb onto the laponite® surfaces, causing interesting dynamic behavior, including transitions from arrested states to liquid states as the concentration and molecular weight of PEO is increased. This re-entrant behavior has been attributed to formation of particle clusters induced free PEO chains. Our DLS results are consistent with a slow diffusive dynamic process, suggesting the formation of large particle clusters, in samples at aging times < 75 days (Figure 1). By contrast to behavior observed in laponite® dispersions with a non-adsorbing polymer, poly(acrylic acid) (PAA), diffusion coefficients of these clusters in the laponite®-PEO systems continue to decrease with aging time until samples reach an arrested state. Finally, interfacial rheology and passive microrheology also show some evidence of re-entrant behavior, although the polymer concentrations at which this occurs do not exactly correspond to the conditions under which re-entrant behavior is observed in bulk rheology
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Surita Bhatia and Bingqian Zheng, "Cluster formation during aging of colloid-polymer dispersions and re-entrant rheological behavior at interfaces and the microscale" in "Colloidal, Macromolecular and Biological Gels II", Samiul Amin, Manhattan College, USA Saad Khan, North Carolina State University, USA Srini Raghavan, University of Maryland College Park, USA Eds, ECI Symposium Series, (2019). https://dc.engconfintl.org/cmb_gels_ii/6