Regensburg 2013 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 33: Poster II

DY 33.13: Poster

Thursday, March 14, 2013, 17:00–19:00, Poster C

Shear banding in drying colloidal dispersions — •Pree-cha Kiatkirakajorn and Lucas Goehring — Max Planck Institute for Dynamics and Self-Organization, Bunsenstrasse 10, D-37075 Göttingen, Germany

During drying, colloidal dispersions undergo complex transformations such as solidification, buckling, cracking and the draining of liquid from pores. These interesting observations suggest how defects and shear localization can arise during the drying of colloidal dispersions. During this process, series of bands appear rapidly behind the solidification front and propagate away from the drying front +/-45°. The emergence of bands have never been explained, although we suggest that these may be the result of shear banding. Here we experimentally show that, during drying, particles of polystyrene dispersion are forced closer to each other so that it crystallizes into a weak solid at some critical volume fraction. Furthermore, solidification is caused by electrostatic charge and Van der Waals force. As this weak solid is further compressed, it responds to the stress during solidification by forming a herringbone pattern of parallel light and dark stripes which can be observed and measured under a microscope. We have measured the film thickness, drying rate, and the band spacing under different drying conditions and salt concentrations, which affect the magnitude of the electrostatic interaction.