Direct Self-Assembly of Cholesteric Liquid Crystal Polyesters on Silicon Surfaces by Solvent Casting Techniques

Autor: Tejedor, Paloma, Fayos, José, Pérez Méndez, Mercedes
Jazyk: angličtina
Rok vydání: 2013
Předmět:
Zdroj: Digital.CSIC. Repositorio Institucional del CSIC
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Popis: The direct self-assembly of two cholesteric liquid-crystal polymers on Si (111) substrates attained by solvent casting methods (spin coating and dip coating) are studied by atomic force microscopy (AFM).
Synthetic cholesteric liquid-crystal-polymers (ChLCP) [C26H20O8]n and [C34H36O8]n, having the same mesogenic rigid group along the helical main chain but different side chain length, are biocompatible and optically active, and exhibit optical rotatory dispersion (ORD), complex circular dichroism (CD), transmittance and reflectance characteristics that make them suitable for the fabrication of photochromic-response displays, lasers and MEMs. For most of these applications casting of the polymers onto technologically relevant substrates by low-cost and simple deposition methods is highly desirable. In this work, we have investigated by atomic force microscopy (AFM) the direct self-assembly of both polymers on Si (111) substrates by solvent casting methods. Spin coating of the polymers dispersed in alkyl-alcohol media leads to the formation of round or ring-shaped aggregates on the semiconductor surface. By using a dip coating technique, both polymers assemble into layered deposits via multilayer growth of two-dimensional islands, evidencing the existence of step edge barriers to downward mass transport. In addition, we have found a variation of the step height with each layer deposited, consistent with a progressive decrease of the molecules tilt relative to the surface normal. The ChLC-polymer/semiconductor surface interaction mechanism has been further investigated by means of molecular mechanical (MM) models, matching simultaneous small and wide angle X-ray scattering (SAXS/WAXS) experiments performed with synchrotron radiation monochromatic beam (1.5 Å) and NMR spectra. Both simulations and experiments support an atomic self-organization of the cholesteric liquid-crystals on the Si surface due to an amphiphilic non-covalent interaction, consistent with the specific morphological features observed by AFM.
Databáze: OpenAIRE
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