Preparation, structural and NLO-optical characterization of LB-molecular films from asymmetric Bent-Core liquid crystals
Por:
Garc´ia-V´azquez P., Morales-Saavedra O.G., Carre´on-Castro M.D.P., Pelzl G.
Publicada:
1 ene 2014
Categoría:
Physics and Astronomy (miscellaneous)
Resumen:
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, measurementsevidence 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 ßeff -coefficient along the polar axes of the 2D-polarLC-compound within the mechanical stable LB-monolayer arrangements.
Filiaciones:
Garc´ia-V´azquez P.:
Instituto de Ciencias Nucleares, Universidad Nacional Aut´onoma de M´exico, Circuito Exterior Ciudad Universitaria, Cd. Universitaria, Apartado Postal 70-543, Coyoac´an, M´exico D. F., 04510, Mexico
Morales-Saavedra O.G.:
Centro de Ciencias Aplicadas y Desarrollo Tecnol´ogico, Universidad Nacional Aut´onoma de M´exico, CCADET-UNAM., Circuito Exterior S/N, Ciudad Universitaria, Apartado Postal 70-186, C.P. M´exico D.F., 04510, Mexico
Carre´on-Castro M.D.P.:
Instituto de Ciencias Nucleares, Universidad Nacional Aut´onoma de M´exico, Circuito Exterior Ciudad Universitaria, Cd. Universitaria, Apartado Postal 70-543, Coyoac´an, M´exico D. F., 04510, Mexico
Pelzl G.:
Institut fur Physikalisches-Chemie, Martin Luther University, Halle-Wittenberg, Mu¨hlpforte 1., Halle, D-06108, Germany
|