Dresden 2009 – wissenschaftliches Programm
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DY: Fachverband Dynamik und Statistische Physik
DY 24: Pattern formation in colloidal and granular systems I
DY 24.5: Vortrag
Donnerstag, 26. März 2009, 15:45–16:00, ZEU 255
Network formation in liquid crystal-colloidal-suspensions — •Marcel Roth, Günter K. Auernhammer, and Doris Vollmer — Max-Planck-Institut für Polymerforschung, Mainz, Germany
When cooling a mixture of thermotropic liquid crystal (5CB) and micrometer-sized colloids (PMMA) from the isotropic to the nematic state a self-supporting network is formed. Within this network the pores are filled with colloid-free nematic liquid crystal while the colloids are concentrated in the walls leading to a low frequency elastic modulus of up to 105Pa.[1]
In this talk we present the results of measurements with a self-made piezo-rheometer in shear mode. Since the applied strain is in the order of only 10−4 the network formation is not affected by the measurement and results are well reproducible. Moreover, the intrinsic frequency range spans four orders of magnitude accessing even 1kHz. With a suitable temperature control we monitor the extended viscoelastic response in dependence on temperature. We show that the low frequency elastic plateau is followed by a strongly viscoelastic region at higher frequencies. In addition the whole spectrum shows a pronounced temperature dependence as cooling deeper into the nematic region.
The rheological data is combined with microscopic images. Here special emphasis will be laid to the transition from a 2D to a 3D-structure varying cooling rates and sample thicknesses.
[1] Vollmer et al., Langmuir 21, 4921-4930 (2005)