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Orientations of Liquid Crystals in Contact With Surfaces That Present Continuous Gradients of Chemical Functionality

Published

Author(s)

Brian H. Clare, Kirill Effimenko, Daniel A. Fischer, Jan Genzer, Nicholas L. Abbott

Abstract

We report the formation of continuous spatial gradients in the density of grafted semifluorinated chains on silicon oxide surfaces by vapor phase diffusion of semifluorinated silanes. We quantify the orientations of a nematic liquid crystal (LC) on these surfaces as a function of local surface composition obtained by using NEXAFS. These measurements demonstrate that it is possible to obtain the full range of tilt angles of a LC on these surfaces by continuous control over the density of semifluorinated silanes grafted onto the surfaces. We also use the data provided by these gradient surfaces to test hypotheses regarding the nature of the interaction between the LCs and surfaces that give rise to the range of tilted orientations of the LCs. We conclude that the orientations of the LCs are not determined by the density of grafted semifluorinated chains nor the density of residual hydroxyl groups presented at these surfaces following reactions with the silanes. Instead, our results lead to the proposition that the tilt angles of the semifluorinated chains on these surfaces (which are a function of the density of the grafted chains) may influence the orientation of the LCs. These results, when combined, demonstrate the potential utility of gradient surfaces for screening surface chemistries that achieve desired orientations of LCs as well as to rapidly assemble experimental data sets that can be used to test propositions regarding mechanisms of anchoring of LCs at surfaces.
Citation
Chemistry of Materials
Volume
18

Keywords

gradients, liquid crystals, NEXAFS, orientation

Citation

Clare, B. , Effimenko, K. , Fischer, D. , Genzer, J. and Abbott, N. (2006), Orientations of Liquid Crystals in Contact With Surfaces That Present Continuous Gradients of Chemical Functionality, Chemistry of Materials (Accessed June 23, 2024)

Issues

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Created May 10, 2006, Updated October 12, 2021