(257a) First Principles-Based Design of Surfaces for Adsorbate-Triggered Anchoring Transitions in Liquid Crystals
This presentation will describe the use of electronic structure calculations to design surfaces that orient liquid crystals and trigger orientational ordering transitions in liquid crystals in the presence of small molecule adsorbates.1,2 The work is motivated by past studies that have demonstrated that surface-induced ordering of liquid crystals depends strongly on the chemical functionality of the surface to which they bind.3 In particular, the liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) has been shown experimentally to assume a perpendicular orientation on surfaces presenting certain metal salts, and to transition to a parallel orientation upon exposure to small molecule adsorbates such as dimethyl methylphosphonate (DMMP).4 To provide insight into the origins of these adsorbate-triggered anchoring transitions and to provide guidance to future experiments, we have used detailed electronic structure calculations to develop a theoretical model for this displacement process based on evaluation of the heat of adsorption of DMMP and 5CB to specific metal cations. The model reproduces experimental displacement trends, including qualitative information about the sensitivity of the metal-5CB system to various concentrations of DMMP. The model is general and has also been extended to predict designs of new classes of surfaces at which anchoring transitions in liquid crystals can be triggered by the adsorption of chemical species other than DMMP. Overall, these results provide guidance to the design of chemo-responsive materials based on chemically functionalized surfaces and liquid crystals, including interfaces potentially useful for chemical sensing.
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