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Buckling and Crumpling of Drying Droplets of Colloid−Polymer Suspensions
journal contribution
posted on 2006-07-04, 00:00 authored by Yoichi Sugiyama, Ryan J. Larsen, Jin-Woong Kim, David A. WeitzSpray drying of complex liquids to form solid powders is important in many industrial applications. One of the
challenges associated with spray drying is controlling the morphologies of the powders produced; this requires an
understanding of how drying mechanics depend on the ingredients and conditions. We demonstrate that the morphology
of powders produced by spray drying colloidal polystyrene (PS) suspensions can be significantly altered by changing
the molecular weight of dissolved poly(ethylene oxide) (PEO). Samples containing high-molecular-weight PEO produce
powders with more crumpled morphologies than those containing low-molecular-weight PEO. Observations of drying
droplets suspended by a thin film of vapor suggest that this occurs because the samples with high-molecular-weight
PEO buckle earlier in the drying process when the droplets are larger. Earlier buckling times are likely caused by
the decreased stability, demonstrated by bulk rheology experiments, of PS particles in the presence of high-molecular-weight PEO at elevated temperatures. We present a consistent picture in which decreased particle stability hastens
droplet buckling and leads to more crumpled powder morphologies; this underscores the importance of interparticle
forces in determining the buckling of particle-laden droplets.