Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 7: POSTERS Rheology
CPP 7.19: Poster
Montag, 25. Februar 2008, 16:45–19:00, Poster A
Influences of Added Salt on the Drying Behavior of Polymer Dispersions - Simultaneous Use of Magnetic Resonance Profiling and Diffusing-Wave Spectroscopy — •Alexander König1, Peter McDonald2, Joseph Keddie2, and Diethelm Johannsmann1 — 1Institute of Physical Chemistry, Clausthal University of Technology, Germany — 2Department of Physics, University of Surrey, UK
Magnetic Resonance Profiling (MRP) was used to measure the non-uniform drying of charge-stabilized polymer dispersions. Drying is sometimes accompanied by packing of particles at the top of the film. In this case, the vertical distribution of free water, φwat(z), is strongly asymmetric. It is suspected - but not well investigated - that particle packing and coalescence create a skin. This process should be influenced by the interaction potential between particles (which can be influenced via addition of salt). As a measure of asymmetry, the skewness of the distribution φwat(z) was used. The skewness is defined as m3/m23/2, where mi is the i-th moment of the distribution.
Diffusing-Wave Spectroscopy (DWS) probes the translational dynamics in concentrated dispersions. Both techniques were combined in-situ in order to correlate structure and dynamics.
The skewness, as determined with MRP, correlated well with the occurence of a static scattering component in DWS. Skin formation is stronger in the presence of salt, which is explained by a destabilizing effect of salt onto the interparticle membranes. Comparing different salts, we found that their relative influence onto interparticle coalescence followed the Hofmeister series.