Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 39: Wetting, Micro and nanofluidics II

CPP 39.4: Topical Talk

Friday, March 30, 2012, 10:15–10:45, C 243

Guided and spatio-selective transport via anisotropic fluid flows — •Anupam Sengupta and Christian Bahr — Max-Planck-Institute for Dynamics and Self-Organization, Göttingen, Germany

Microscale flow of anisotropic fluids [1,2] (nematic liquid crystals) offers a novel approach in the realm of transport phenomena. We study the transport of colloidal particles, either isolated or self-assembled chains, flowing in a nematic matrix through microfluidic channels. We demonstrate the influence of the nematic director field on the spatial orientation of the particles and the guidance of the particles by flow-induced topological defect structures of the nematic matrix. The transport of colloidal entities can be additionally tuned using an external field or by means of smart microfluidic architecture. In addition to flow parameters and channel dimensions and geometry, significant influence of the equilibrium molecular orientation of the liquid crystal on the channel walls (surface anchoring) has been observed. Surface anchoring of the molecules affects the evolution and sustenance of flow-induced phenomena in liquid crystals. This plays a pivotal role in the transport process, effectively providing us the route to guided and/or stereo-selective transport of colloidal particles over large length scales. Such phenomena are in contrast to isotropic fluids. The transport phenomena are characterized using a combination of polarising optical microscopy and fluorescence confocal polarizing microscopy.

[1] A. Sengupta, S. Herminghaus and Ch. Bahr, Mol. Cryst. Liq. Cryst. 547, 203 (2011).

[2] A. Sengupta, U. Tkalec and Ch. Bahr, Soft Matter 7, 6542 (2011).