Prof. Nicholas L. Abbott: Effects of Confinement on the Ordering of Liquid Crystals: Surprises that Lead to Sensors

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    Effects of Confinement on the Ordering of Liquid Crystals:  Surprises that Lead to Sensors

    Prof. Nicholas L. Abbott, University of Wisconsin-Madison, Madison WI, USA

This presentation will address recent experimental investigations of the ordering of liquid crystals within micrometer-sized droplets that are dispersed in water.   The first part of the talk will describe the design of an experimental system that allows precise control over the size and interfacial chemistry of liquid crystalline droplets.   Experimental observations of size-dependent ordering of the liquid crystals within the droplets will be shown to differ from widely reported scaling arguments for the relative contributions of surface and elastic effects to the free energy of confined liquid crystals.   The second part of the talk will address unexpected observations regarding the effects of picogram per milliliter concentrations of bacterial endotoxin on ordering transitions in micrometer-size liquid crystalline droplets.  The ordering transitions, which occur at surface concentrations of endotoxin that are less than 10^-5 Langmuir, are not due to adsorbate-induced changes in the interfacial energy of the liquid crystal.  The sensitivity of the liquid crystal to endotoxin was measured to change by six orders of magnitude with the geometry of the LC (droplet versus slab), providing support for our hypothesis that the interactions of the endotoxin with topological defects in the liquid crystal mediate the response of the droplets.  The liquid crystal ordering transitions depend strongly on glycophospholipid structure and provide new designs for highly sensitive sensors for bacterial contamination*.

*I-H. Lin, D.S. Miller, P.J. Bertics, C.J. Murphy, J.J. de Pablo, and N.L. Abbott; Science, 19 May 2011