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Revista mexicana de física

versão impressa ISSN 0035-001X


GARCIA-VAZQUEZ, P.; MORALES-SAAVEDRA, O.G.; CARREON-CASTRO, M.D.P.  e  PELZL, G.. Rev. mex. fis. [online]. 2014, vol.60, n.5, pp.390-400. ISSN 0035-001X.

Molecular mono- and multilayered films of a polar asymmetric bent-core ("banana-shaped") liquid crystalline (LC) compound with hydrocarbon end-chains were prepared by the Langmuir-Blodgett (LB) technique. Langmuir films were characterized by surface pressure isotherms and Brewster angle microscopy (BAM). Likewise, LB-films deposited onto glass substrates were characterized by UV-VIS spectroscopy, the optical second harmonic generation (SHG) technique and atomic force microscopy (AFM). Results show that the asymmetric structure of bent-core liquid crystals may promotes an unstable multi-layered (n > 10 LB-layers) LB-architecture which leads to a rapid collapse of Z-type arrangements, giving rise to a drastic decrease of the nonlinear optical (NLO) properties and film quality. Indeed, measurements evidence a tolerable and uniform molecular coverage on the glass substrates with anisotropic orientational distribution for a moderate number of layers only (n ≤ 10 LB-layers); where, according to NLO-experimental data, the net molecular polarization is aligned outward the substrate layer. This observation leads us to implement a simplified model based on the monomeric rod-like approximation, in order to estimate significant NLO-tensorial components and an effective molecular hyperpolarizability βeff -coefficient along the polar axes of the 2D-polar LC-compound within the mechanical stable LB-monolayer arrangements.

Palavras-chave : Langmuir-Blodgett films; non linear optics; liquid crystals; Bent-Core mesogens.

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