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Séminaire Rik Wensink

Cholesteric order of coiled nanorods

Rik Wensink

Institute for Theoretical Physics II : Soft Matter
Heinrich Heine University Duesseldorf, Germany

Cholesteric order is ubiquitous in liquid crystal materials and is best known for its ability to induce extraordinary optical rotational power as employed in e.g. displays. Understanding the behaviour of the cholesteric pitch from microscopic principles however is a non-trivial problem and poses serious theoretical challenges.

In this talk I will discuss the cholesteric properties of systems of coiled Yukawa rods as a simple prototype model for chiral rod-like macromolecules (such as DNA or filamentous virus particles) which are often characterized by a helical organization of surface charges.

The behaviour of the cholesteric pitch turns out to be very sensitive to the density or temperature of the system as well as the internal (microscopic) pitch of the Yukawa rods. At certain values of the internal pitch a sudden change of symmetry of the cholesteric state from left- to right-handed occurs upon variation of the density. These findings provide a theoretical underpinning for the so-called ’pitch inversion’ observed in cholesteric materials and show that the effect might be observed more generally in systems of coiled mesogens with a fixed internal chirality.