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| - Orientations of Liquid Crystals in Contact with Surfaces thatPresent Continuous Gradients of Chemical Functionality
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| - Surfaces prepared with continuous gradients in chemical functionality template continuous changes in the orientations of nematic liquid crystals. Gradient surfaces also provide data sets that can be used to test hypotheses regarding the mechanisms of interactions of liquid crystals with surfaces.
- We report the formation of continuous spatial gradients in the density of grafted semifluorinated chainson silicon oxide surfaces by vapor-phase diffusion of semifluorinated silanes. We quantify the orientationsof the nematic liquid crystal (LC) 4-cyano-4‘-pentylbiphenyl on these surfaces as a function of localsurface composition obtained by using NEXAFS. These measurements demonstrate that it is possible toobtain the full range of tilt angles of a LC on these surfaces. We also use the data provided by thesegradient surfaces to test hypotheses regarding the nature of the interaction between the LC and surfacesthat give rise to the range of tilted orientations of the LC. We conclude that the orientations of the LCare not determined solely by the density of grafted semifluorinated chains or by the density of residualhydroxyl groups presented at these surfaces following reactions with the silanes. Instead, our resultsraise the possibility that the tilt angles of the semifluorinated chains on these surfaces (which are a functionof the density of the grafted chains) may influence the orientation of the LC. These results, when combined,demonstrate the potential utility of gradient surfaces for screening surface chemistries that achieve desiredorientations of LCs as well as for rapidly assembling experimental data sets that can be used to testpropositions regarding mechanisms of anchoring LCs at surfaces.
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