Regensburg 2010 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 30: Poster: Micro and Nanofluidics

CPP 30.2: Poster

Wednesday, March 24, 2010, 17:30–19:00, Poster C

Evidence for the Absence of the Shear Viscosity Minimum of the Confined Liquid Crystal 8OCB — •Dominik Gerstner, Simon Gruener, and Patrick Huber — Physics of Mesoscopic Systems, Saarland University, Saarbruecken

We present measurements on the capillary rise (spontaneous imbibition) of the lqiuid crystal 8OCB into silica monoliths (porous Vycor) permeated by tortuous pores with radii of 5 nm. The invasion dynamics have been recorded measuring the sample’s mass increase m(t) due to the liquid uptake. All obtained curves obey the classical Lucas-Washburn law, thus corroborating bulk-like flow behavior even in such extreme spatial confinement. However, the shear viscosity minimum characteristic of the flow of a nematic liquid crystal is found to be absent. This behavior corroborates the assumption of a paranematic phase beyond the I-N-transition temperature caused by an orientational ordering of the molecules induced by the confining cylindrical pore walls. Optical birefringence measurements on 8OCB in aligned silica nanochannels further support this hypothesis. This work has been supported within the DFG priority program 1164, Nano- & Microfluidics (Grant No. Hu 850/2).