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BIRS Workshop Lecture Videos

Active nematics at interfaces: conditioning and steering effects Sagues, Francesc


Active liquid crystals are a new class of soft materials that have recently raised a huge interest. In particular, reconstituted suspensions of cytoskeletal filaments and associated motor proteins have proven ideal for quantitative studies of the origin of subcellular or- ganization. Here we refer to the system initially engineered by the group of Z. Dogic, consisting of bundled microtubules powered by ATP-fueled kinesin motors. We concen- trate on two-dimensional preparations showing nematic textures and streaming flows, from largely-organized to seemingly chaotic. We will present results on different scenar- ios where this active nematics system is conditioned with interfacial fluids. The simplest situation corresponds to prepare them in contact with isotropic oils of different viscosities. From this we can extract a prediction for the as of now unknown shear viscosity of the nematic film. More striking is the situation when the contacting passive fluid is a liquid crystal in its smectic phase. In this latter situation a totally unprecedented strategy of control of the active flows has been recently demonstrated. Other scenarios correspond- ing to encapsulated active nematics, both in contact with isotropic and anisotropic oils will be briefly presented.

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