Dresden 2014 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 29: Colloids and Complex Liquids I
CPP 29.5: Vortrag
Mittwoch, 2. April 2014, 10:30–10:45, ZEU 114
Shear banding in colloidal dispersions — •Pree-cha Kiatkirakajorn1,2 and Lucas Goehring1 — 1Max Planck Institute for Dynamics and Self-Organization, Am Fassberg 17, D-37077 Göttingen, Germany — 2Faculty of Physics, University of Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen,Germany
During the drying of colloidal dispersions, a pattern of bands frequently appears in the film behind the drying front, and oriented at an angle of 45° to the drying front line. The nature of these bands has never been explained, although they have been suggested to be shear-banding based on a visual similarity to these in metals. Through microscopy of colloidal polystyrene (98-298 nanometers), we confirm that the bands are associated with local shear strains. We show how defects and shear localization arises during the drying of colloidal dispersions, and how a driving force for the bands arises from the compression of the dispersions during solidification. Further, we find that the spacing of the shear bands correlates with the film thickness, suggesting a mechanical release of stress, similar to cracking. When a new shear band starts, it can propagate either forwards or backwards, at a speed much greater than the drying front speed. Adding salt (between 0-30 mM NaCl) into the drying dispersions causes a reduction in spacing and the ultimate disappearance of the shear bands. All these observations are consistent with the simple explanation that the bands are a shear-localizing instability, caused by colloidal interactions during the directional solidification of colloidal dispersions and suggest how they can be controlled or eliminated.