Bayreuth 1998 – wissenschaftliches Programm
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SYA: Symposium Kolloide Systeme und Polyelektrolyte
SYA 3: Kolloidale Systeme und Polyelektrolyte
SYA 3.3: Vortrag
Montag, 9. März 1998, 17:00–17:20, H18
High Frequency Viscoelasticity of Concentrated Colloidal Dispersions — •N. Willenbacher1, J. Bergenholtz2, F.M. Horn3, W. Richtering3, and N.J. Wagner4 — 1BASF AG, Polymer Research Div., 67056 Ludwigshafen — 2Inst. Physik., Univ. Konstanz — 3Inst. Makromol. Chem., Univ. Freiburg — 4Dept. Chem. Eng., Univ. Delaware, Newark
The high frequency viscoelasticity of concentrated dispersions has been characterized using a mechanical torsional resonator. The high frequency viscosity η∞′ is dominated by the hydrodynamic interactions among the colloidal particles while the modulus G∞′ primarily contains the thermodynamic (e.g. electrostatic and steric) forces. Starting from Zwanzig and Mountains equation an equivalent hard sphere model is presented for the case of thin double layers which simplifies the statistical mechanical equations significantly and relates G∞′ directly to Q. The results from PBMA model dispersions of known ionic strength and pH are compared with data from conductometric titration and electrokinetic measurements and are interpreted within the framework of the DLVO theory. With respect to η∞′ hard sphere behaviour is found irrespective of ionic strength (i.e. screening of Coulomb interaction) and fluid structure (liquid, crystalline, or glassy). Short time self diffusion coefficients Dss of concentrated, but liquid dispersions determined by FOQELS show the same behaviour and Dss(φ) is related to η∞′(φ) by a generalized Stokes-Einstein equation.