Meso-scale imaging of patterned surfaces by decoration with liquid crystals

Abstract

We report techniques for the imaging of patterned surfaces that are based on the use of random arrays of microdroplets of the nematic liquid crystal 4-cyano-4′-pentylbiphenyl (5CB). Microdroplets of 5CB were delivered to surfaces by spray atomization of a nematic phase or by condensation of a vapor of mesogens. By comparing the optical textures of microdroplets of 5CB in their isotropic and nematic states, we conclude that microdroplets of liquid crystals (LCs) can be used to image patterned surfaces that cannot be imaged by using microdroplets of isotropic liquids (conventional ‘breath figures’). We demonstrate, for example, the use of random arrays of microdroplets of nematic 5CB to image (i) patterned, low-energy SAMs formed from H 3C(CH 2) 14SH and H 3C(CH 2) 15SH on films of gold and (ii) gold films that are patterned with regions that differ in their roughness (on the 1–10 nm scale) and which support SAMs formed from H 3C(CH 2) 14SH. On the low energy surfaces, we observed the optical appearances of the microdroplets of LCs to be indifferent to their manner of deposition (spray or condensation) but dependent on their size. In particular, when using microdroplets with diameters <∼45 μm, the optical appearances of the microdroplets were insensitive to the structures of the surfaces on which they were deposited. However, by using larger microdroplets and by observing the optical structure within a given microdroplet of LC, it was possible to image patterns with lateral dimensions substantially smaller than 45 μm. We also report the use of nematic 5CB to image patterned, high energy SAMs formed from HOOC(CH 2) 10SH and NaOOC(CH 2) 10SH that are uniformly wet by both isotropic and nematic liquids.