Abstract
We have created nanospirals by self-assembly during droplet evaporation. The nanospirals, 60–70 nm in diameter, formed when solvent mixtures of methanol and m-cresol were used. In contrast, spin coating using only methanol as the solvent produced epitaxial films of stripe nanopatterns and using only m-cresol disordered structure. Due to the disparity in vapor pressure between the two solvents, droplets of m-cresol solution remaining on the substrate serve as templates for the self-assembly of carboxylic acid molecules, which in turn allows the visualization of solution droplet evaporation one molecule at a time.
Highlights
Patterns formed by solvent evaporation are relevant to various coating processes as well as patterning technology
A well-known example of substrate-dominated self-assembly is the epitaxial stripe nanopatterns formed by alkanes and alkane derivatives on highly oriented pyrolytic graphite (HOPG) [4,5,6,7,8,9,10]
The 1,3-methylene group distance, 0.251 nm, of alltrans alkyl chains matches the distance of the nearest neighbor of the HOPG lattice, 0.246 nm, along, e.g., the [11 2 0] crystallographic direction
Summary
Patterns formed by solvent evaporation are relevant to various coating processes as well as patterning technology. The head-to-head arrangement gives rise to the stripe nanopattern whose periodicity is 1 × or 2 × the molecular chain length Such nanopatterns serve as model templates for the study of site-specific adsorption, alignment, assembly, and reaction of small molecules [8,9,11,12] as well as macromolecules [13,14,15,16]. C20A nanorods with 1.0 nm in thickness and 5.4 nm in width are nucleated directly on the nanoparticle to produce nanoparticle/nanorod hybrid structure [17] We present another method to perturb the epitaxial interaction between long-chain carboxylic acids and HOPG and to create spiral nanopatterns by adding a co-solvent to the spin coating solution.
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