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

Abstract

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.

Magnetic Assembly of Eu-Doped NaYF4 Nanorods for Field-Responsive Linearly and Circularly Polarized Luminescence

“…Since linear birefringence is the difference between its ordinary and extraordinary refractive indices (Δ n ), we used the equation I = I 0 sin 2 (2α) sin 2 (πΔ nL /λ) to estimate the Δ n of thin films observed under a polarizing microscope, where I 0 is the intensity of light passing through the first polarizer; I is the intensity of light passing through the second polarizer; α is the angle between the transmission axes of the polarizer and the long axis of the thin film; L is the sample thickness; λ is the wavelength of incident light; and Δ n is the linear birefringence . The linear birefringence of the chiral and linear thin film was estimated to be 0.04 and 0.17, respectively.…”

Birefringent polyvinyl alcohol layers as retardation components for display devices

“…The birefringence of the PVA foils was measured at the standard 589 nm wavelength by interferometric method, polarization ellipse method, channeled spectra method and polarized light refraction method, which were previously detailed 27 . The photos of each experimental setup used in this work are shown in Scheme 2.…”

“…For this reason, the birefringence of polymers must be carefully determined by proper experimental means. Several optical methods were developed to measure this optical parameter and they rely on various phenomena, such as interference, change in ray polarization state, channeled spectra and refraction 27 …”

“…Several optical methods were developed to measure this optical parameter and they rely on various phenomena, such as interference, change in ray polarization state, channeled spectra and refraction. 27 Among the polymers employed as optical elements in LCD devices, polyvinyl alcohol (PVA) presents significant potential as retardation layer owing to its excellent optical-film features, like enhanced high transparency, good thermal resistance, and low refraction index.…”

Birefringence Behaviors of Cellulose Nanocrystals under Varied Concentrations, Ultrasonication Treatments, and Different Solvents

“…Birefringence is typically observed in anisotropic materials, which have different optical properties in different crystallographic directions. Alternative application of birefringence in material such as like light modulators, optical storage discs, and phase retardation films, the polymer layer needs to exhibit a significant degree of birefringence [1]. Cellulose nanocrystal (NCC) with high crytallinity supposed to IOP Publishing doi:10.1088/1755-1315/1309/1/012003 2 have this behavior at concentrations threshold.…”