Influence of UV and Gamma radiations on the induced birefringence of stretched poly(vinyl) alcohol foils

Nechifor, Cristina‐Delia; Zelinschi, Carmen Beatrice; Dorohoi, Dana Ortansa

doi:10.1016/j.molstruc.2014.01.011

Cited by 8 publications

(14 citation statements)

References 24 publications

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“…The stretched PVA films are uniax media with optical axis parallel to the stretching direction. The optical birefringence of the polymer foils can be measured directly by using compensatory devices, or the main refractive indices n e and n o can be measured separately with linearly polarized radiations by using an interferometer …”

Section: Experimental Partmentioning

confidence: 99%

“…The polymer foil introduced between crossed polarizers changes the light polarization state as a function of the phase difference, ΔΨ = (2π/λ)ΔnL, introduced between ordinary and extraordinary components. The phase difference introduced by the polymer foil is compensated by BC, standardized in yellow monochromatic radiation of a Na lamp.…”

Section: Experimental Partmentioning

confidence: 99%

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Induced birefringence of rubbed and stretched polyvinyl alcohol foils as alignment layers for nematic molecules

Nechifor

Postolache

Albu³

et al. 2019

Polymers for Advanced Techs

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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...

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Section: Experimental Partmentioning

confidence: 99%

Section: Experimental Partmentioning

confidence: 99%

Induced birefringence of rubbed and stretched polyvinyl alcohol foils as alignment layers for nematic molecules

Nechifor

Postolache

Albu³

et al. 2019

Polymers for Advanced Techs

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“…12, d). From testing the PUR polyurethane sample to the contact pressure, it is observed that it behaves well on a large contact surface [14,15].…”

Section: Figure 11 Contact Pressure Application Test -Pur Virtual Pol...mentioning

confidence: 99%

Virtual Studies on the Behavior of Polyurethane on Mechanical Stresses

Negrea

Enescu

Stoian

et al. 2022

Scientific Bulletin of Valahia University - Materials and Mechanics

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In this part of the paper, we will study the behavior of PUR polyurethane at different mechanical and thermal stresses, stresses for which this material behaves very well. It is known that this material behaves well as a protective material against shocks, so it is used as protection against mechanical elements. PUR behaves excellently at uneven static stresses and dynamic stresses. That is why it is used in the construction of the rollers of medium weight mobile devices or rollers that have cam functionality, strongly required for static and dynamic contact. PUR has very good thermal properties, it is used as a thermal insulator when it is in the form of high-density polyurethane foam (PUR / PIR).

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“…PVA films have multiple applications due to their environmental friendliness, easy processing, and low costs [19,20]. The properties of the PVA polymer films can be easily modified by external actions [21][22][23].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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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.

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Influence of UV and Gamma radiations on the induced birefringence of stretched poly(vinyl) alcohol foils

Cited by 8 publications

References 24 publications

Induced birefringence of rubbed and stretched polyvinyl alcohol foils as alignment layers for nematic molecules

Induced birefringence of rubbed and stretched polyvinyl alcohol foils as alignment layers for nematic molecules

Virtual Studies on the Behavior of Polyurethane on Mechanical Stresses

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

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