Effect of mechanical treatments on orientation behavior and spectral properties of azoderivative dyes incorporated in poly(vinyl alcohol) films

Review on Optical Methods Used to Characterize the Linear Birefringence of Polymer Materials for Various Applications

Optical polymers are recognized for their high transparency, raised flexibility, low cost, and good film-forming ability; hence, they introduce a multitude of benefits in a wide range of devices, such as information storage, displays, optical communications, and filters. Among the optical properties, birefringence is an essential parameter in practical cases that demand the control of the state of polarization of light. This review is focused on describing some fundamental and applicative aspects concerning the optical birefringence of the polymer materials. First, elementary notions depicting the phenomenon of light double refraction in macromolecular media are provided. Furthermore, the most relevant optical techniques to determine birefringence are reviewed by highlighting the working principle and mathematical basis for computing this parameter. Then, a series of investigations of optically birefringent polymers are described, summarizing the most utilized approaches to induce light double refraction in such materials. The selected results are analyzed in relation to the pursued applications. In the end, the future of this scientific domain is briefly presented by establishing the research paths that need further exploration. Moreover, the novel directions that could be formulated and might contribute to certain considerable advancements in the materials employed in the modern optical technologies are mentioned.

Polyimide-Derived Supramolecular Systems Containing Various Amounts of Azochromophore for Optical Storage Uses

The progress of digital technologies demands more speed and larger storage capacity. Optical storage systems have the advantage of being cheap, fast and capacious. This article explores the potential use of polyimide-based films as a recording medium for optical storage devices. The materials were designed through a host-guest approach that involves a cyano-containing polyimide precursor and an azochromophore combined in the following ratios: 1:0.25, 1:0.5, 1:0.75 and 1:1. After thermal treatment up to 200 °C, polyimide systems were formed with supramolecular structures constructed via hydrogen bonding as shown by molecular modeling and FTIR at around 3350 cm^-1. The aspects arising from the variation of the azo-dye content in the polyimide samples and their impact on the vitrification temperature, colorimetric features, refractive index, band gap, non-linear optical susceptibility and birefringence were investigated for the first time. The thermal analysis indicated a slight decrease in the vitrification temperature from 190.84 °C for the sample without azo dye to 163.91 °C for the film containing the highest leading of azo dye. The morphology images revealed the occurrence of periodic structures in azo-derived materials exposed to a UV laser, which is accentuated by the addition of more azo dye molecules. Optical tests allowed observation of the increase in the dominant wavelength, refractivity and optical conductivity of the samples, produced by the incorporation of azochromophore and laser irradiation. The photo-generated birefringence increased from 0.014 (sample with 1:0.25) to 0.036 (sample with 1:1), which in combination with the created regular topography pattern, is essential for the use of these materials as recording media in optical storage applications.

Birefringence of Thin Uniaxial Polymer Films Estimated Using the Light Polarization Ellipse

A simple method for determining the linear birefringence of the thin layers based on the determination of the orientation of the polarization ellipse of totally polarized light is proposed and it is applied to PVA thin foils. Theoretical notions and the experimental procedure are described. The linear birefringence of polymer thin foils with different degrees of stretching is determined and the applicability of the method is discussed.