Berlin 2012 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 37: Poster: Rheology (joint focus with DRG)
CPP 37.9: Poster
Donnerstag, 29. März 2012, 18:45–19:45, Poster A
Mechanical Properties and Structure in Precipitated Colloidal Silica — •Miao Wang1,2, Marcel Roth1, H. Henning Winter2, and Günter K. Auernhammer1 — 1Max Planck Institute for Polymer Research, Mainz, Germany — 2University of Massachusetts, Amherst, MA, USA
The mechanical properties of colloidal systems strongly depend on structure and interaction potential. Inorganic precipitated silica-gels of various compositions, as widely used as filler in paints, cosmetics and polymers, show this phenomenon. To analyze the correlation between 3D-structure and mechanics we use combined measurements by confocal reflection microscopy, piezo-rheometry, and Couette rheometry. Samples get prepared in a low-viscosity sol state and then transfered into the measurement cell before gelation sets in. In-situ confocal reflection microscopy visualizes the formation of gel. Simultaneously, this process is studied with a piezo-rheometer, which allows dynamic mechanical measurements on samples of less than 100 micrometer thickness. The applied shear strain lies typically below 0.001 (absolute displacement smaller than 100 nm). Classical rheometer measurements with a Couette cell extend the data to lower frequencies. Depending on composition, we find a relaxation process (frequency dependent shear modulus) at low frequencies. This frequency dependence suggests the structural relaxation of the network structure at long times. Structure and properties depend on water content in the sample. An increased water fraction in the gel results in a finer and more connected network with longer relaxation time but lower plateau modulus.