Some optical properties of poly (vinyl alcohol) (PVA) films are investigated prior and after the rubbing and stretching of the samples. Birefringence of the prepared foils is enhanced as their stretching degree and rubbing become larger. These processing factors are also affecting the values of the ordinary and extraordinary refractive indices. The induced anisotropy in PVA foils is evidenced in the morphological characteristics observed by optical microscopy. The spreading and adhesion behaviors of a nematic liquid crystal on PVA foils are analyzed by means of contact angle measurements. Preliminary testing of the nematic on the PVA films revealed significant variations in transmitted light intensity during sample rotation under crossed polarizers. The high contrast between dark and bright patterns is indicative of uniform and homogenous alignment of nematic on the rubbed and stretched PVA foils. KEYWORDS polyvinyl alcohol, birefringence, rubbed, stretching, alignment layer 1 | INTRODUCTION Among the applications of the most known hydrosoluble synthetic polymers, polyvinyl alcohol (PVA) has been used in display industry. 1 Liquid crystal display (LCD) devices are optoelectrical systems, which are mainly working based on the light-modulating properties of nematic liquid crystals (NLCs). 2 The cell contains a liquid crystal (LC) layer placed between two alignment layers (ALs) casted on indium tin oxide (ITO)-covered glass substrates. 3 The cell also contains polarizing plates, electrodes, retardation films, color filters, backlight unit, etc. In the fabrication technology of the LCDs, PVA films are used to manufacture polarizers, 4 retarders, 5,6 optical filters, 7,8 and ALs. 9-12 The ALis a polymer layer coated on the glass plates, which through its textured surface is able to align the NLC molecules. In the absence of AL layers, the NLC molecules would be disposed to orient themselves randomly. 13 The capacity to control the alignment of the NLC on AL surfaces is essential for the performance of LCDs since it is known that weak anchoring of the NLC can significantly reduce the operating voltages and can improve the steepness of the electro-optic response of device. 14 Because NLC molecules follow the alignment imposed by the surface pattern of AL, 1 various techniques were developed to control the NLC orientation through adaptation of the AL surface characteristics. Among these methods, the most reliable ones are stretching, 11 soft lithography, 15 photolithography, 16 nanoimprint lithography, 17 and rubbing. 18 The alignment of NLCs on a surface is affected by the polymer chemical structure and conformation 10,19,20 rubbing strength, 21 type of rubbing cloth, 18,22,23 film thickness, 9 surface roughness anisotropy, 24 and surface wetting characteristics. 25 Currently the display market still uses the rubbing procedure to prepare ALs. The process is quite simple and involves a close contact between the polymer film and the velvet covered rotating cylinder. 26 The pattern formed on the surface of the rubbed polym...

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.

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.

Various azoderivative dyes were incorporated in uncolored poly(vinyl alcohol) (PVOH). One type of film was obtained by drying the layer of solution cast on glass plate. The other type was obtained by rubbing the PVOH layer before complete drying. Linear birefringence and dichroism of dyed polymer films were investigated as a function of stretching degree. An increase in the linear birefringence was found with increasing stretching degree for both uncolored and colored films. Dichroism of the PVOH films depends on the dye chemical structure and also on the stretching degree of both non‐rubbed and rubbed and dyed PVOH samples. Molecular modeling was used to examine interactions occurring between PVOH and the embedded dye molecule. These stretching degree dependencies were approximated mathematically, which was used to describe the behavior of some components of interference filters.

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