Microscopic Orientational Order of Polymer Chains in Helical Polyacetylene Thin Films Studied by Confocal Laser Raman Microscopy

Abstract

Most of the realistic networks are weighted scale-free networks. How this structure influences the condensation on it is a challenging problem. Recently, we make a first step to discuss its condensation [Phys. Rev. E 74 (2006) 036101] and here we focus on its evolutionary process of phase transition. In order to show how the weighted transport influences the dynamical properties, we study the relaxation dynamics in a zero range process on weighted scale-free networks. We find that there is a hierarchical relaxation dynamics in the evolution and there is a scaling relation between the relaxation time and the jumping exponent. The relaxation dynamics can be illustrated by a mean-field equation. The theoretical predictions are confirmed by our numerical simulations.

Three-dimensional imaging of chemical bond orientation in liquid crystals by coherent anti- Stokes Raman scattering microscopy

“…The frequency/wavelength shifts from the monochromatic pump wavelength correspond to the natural frequencies of vibration of individual chemical groups within the molecule. For example, Ofuji et al [10] used Raman microscopy to image solid films of orientationally ordered fibrils in polyacetylene films with contrast based on the C=C bond stretching frequency, while Buyuktanir et al [11] used the cyano (CN) group stretching frequency to image defects in liquid crystal samples. Blach et al [12] developed a theory of polarized Raman microscopy in a birefringent medium and probed the director by using the vibrational mode at 2226 cm -1 .…”

Coherent anti-Stokes Raman scattering polarized microscopy of three-dimensional director structures in liquid crystals

“…2-4, which is ~100,000 times faster than in confocal Raman microscopy [3,4]. The laser powers could be as low as 17mW for the pump wave and 5mW for the Stokes wave.…”

“…However, this approach requires doping a specially selected dye that at small concentrations would provide strong contrast without affecting the LC properties. The labeling-free technique of interest is confocal Raman microscopy [3,4], which utilizes a Raman vibration and the signal dependence on orientations of molecular bonds. To study 3-D molecular orientation patterns, several techniques employ nonlinear processes, such as second harmonic generation (SHG) [5], third harmonic generation (THG) [6], and two-photon fluorescence (TPF) [7].…”

“…Coherent anti-Stokes Raman scattering (CARS) microscopy has been used for visualizing chemical composition in biological and lyotropic systems [8,9]. We report 3-D imaging of LC director structures using CARS polarized microscopy (CARSPM), which does not require doping the LC with dyes and offers chemical selectivity and bond-orientation specificity superior to that of other techniques [2][3][4][5][6][7]; it also provides 5 10 times faster imaging (stronger signal) than confocal Raman microscopy [3,4]. We demonstrate that CARSPM is a viable technique for mapping of 3-D patterns of molecular orientations and LC director dynamics.…”

“…A picosecond Nd:YVO 4 Laser 1 (1064nm, HighQ Laser) with the pulse width ~10 ps and a repetition rate 76MHz is used both as a source of Stokes wave and to synchronously pump Laser 2, a tunable (850-890nm) optical parametric oscillator (OPO, HighQ Laser) with the output of ~10ps pulses. The synchronously pumped OPO coherent device provides temporal synchronization with Laser 1 and serves as a source of the pump wave.…”