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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 29: Colloids and Complex Liquids I

CPP 29.4: Vortrag

Mittwoch, 2. April 2014, 10:15–10:30, ZEU 114

Structural anisotropy of directionally dried colloids — •Lucas Goehring¹, François Boulogne², Ludovic Pauchard², Frédérique Giorgiutti-Dauphiné², Robert Botet², Ralf Schweins³, Michael Sztucki⁴, Joaquim Li⁵, and Bernard Cabane⁵ — ¹MPI Dynamics and Self-Organization, Göttingen, Germany — ²University Paris-Sud, Orsay, France — ³ILL, Grenoble, France — ⁴ESRF, Grenoble, France — ⁵PMMH, ESPCI, Paris, France

There are two main routes for making materials. In many cases the liquid-solid transition results from cooling, as intermolecular forces cause atoms to settle into equilibrium positions. For particulate materials such as ceramics and coatings the usual route is, instead, through the liquid-solid transition that is caused by evaporation from a dispersion of solid particles in a volatile solvent. One often sees this transition as being driven exclusively by the loss of free volume, and the solvent disappears from the description. Here we show, however, that the flow of solvent in a directionally dried colloidal dispersion breaks the orientational symmetry of the liquid and generates a structural anisotropy. This anisotropy arises when the particles have been concentrated by the flow to the point where they are caged by their neighbours into a soft, deformable network. The dispersion then acts as a yield-stress material, and accumulates strain in the direction of solidification, which freezes into the structure of the aggregated solid. To our knowledge, such bulk structural anisotropy has never been reported before, although we show experimentally that it is a robust feature of drying, and affects the optical and mechanical properties of the final solid.