An insight on the effect of rubbing textile fiber on morphology of some semi-alicyclic polyimides for liquid crystal orientation

Barzic, Andreea Irina; Stoica, Iuliana; Popovici, Dumitru; Vlad, Stelian; Cozan, Vasile; Hulubei, Camelia

doi:10.1007/s00289-012-0858-z

Cited by 16 publications

(12 citation statements)

References 40 publications

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“…Rubbing affects the analyzed properties by decreasing the polymer surface polarity, while its dispersive character is augmented (Table ). This is in agreement with previous investigations on rubbed PI containing alicyclic segments …”

Section: Resultsmentioning

confidence: 99%

“…It is presumed that the mechanisms relying on the microgroove formation and the anisotropic arrangement of polymer chains at the film surface are involved in the device performance . In addition, it was showed that depending on the PI structure and the type of the rubbing velvet, one may optimize the uniformity of the AL surface, the anisotropy degree and the microgroove dimensions …”

Section: Introductionmentioning

confidence: 99%

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Insights on Light Dispersion in Semi‐Alicyclic Polyimide Alignment Layers to Reduce Optical Losses in Display Devices

Barzic¹,

Hulubei²,

Stoica³

et al. 2018

Macro Materials & Eng

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Two polyimide structures are prepared from an alicyclic dianhydride and aromatic diamines, containing or lacking fluorine. The polymer films are characterized for display technology purposes. Light dispersion data of the studied samples are compared with those of some nematics to evaluate optical losses in the liquid crystal cell. It is shown for the first time that matching refractive indices of polyimide and nematic at several wavelengths is essential for reduction of Fresnel reflections, thus improving the device performance. Resistivity measurements indicate that rubbing generates a few surface charges on the surface of the fluorine‐derived polymer, which contribute to a more uniform orientation of liquid crystals, as supported by polarized microscopy analysis. Both pristine polyimide films exhibit a smooth surface with isotropic features, which are changed into anisotropic ones after rubbing, as a consequence of microgrooves’ appearance. Their thickness uniformity is affected by the structure of the diamine moieties. The adhesion of all nematics to the polyimide films is enhanced by the rubbing procedure.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Insights on Light Dispersion in Semi‐Alicyclic Polyimide Alignment Layers to Reduce Optical Losses in Display Devices

Barzic¹,

Hulubei²,

Stoica³

et al. 2018

Macro Materials & Eng

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“…Among these methods, the most reliable ones are stretching, soft lithography, photolithography, nanoimprint lithography, and rubbing . The alignment of NLCs on a surface is affected by the polymer chemical structure and conformation rubbing strength, type of rubbing cloth, film thickness, surface roughness anisotropy, and surface wetting characteristics . Currently the display market still uses the rubbing procedure to prepare ALs.…”

Section: Introductionmentioning

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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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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“…The alignment of the molecules can be induced by micrometric or nanometric grooved substrates varying in height, width and spacing (Lamers et al, ). There are many methods used to generate micro‐ and nanopatterned polymer surfaces, such as: electron beam lithography (Loesberg et al, ), nanoimprint lithography (Takahashi et al, ), laser interference lithography and subsequent reactive ion etching (Lamers et al, ; van Soest et al, ), soft lithography (Kocabas and Aydinli, ; Lo and Juang, ; Xia and Whitesides, ), crack‐induced grooving method (Lin et al, ), rubbing with different types of fabric (Barzic et al, ; Stoica et al, ), scanning probe lithography (Fang et al, ) and so on. Unfortunately, all mentioned techniques have two or more fabrication steps.…”

Section: Introductionmentioning

confidence: 99%

An atomic force microscopy statistical analysis of laser‐induced azo‐polyimide periodic tridimensional nanogrooves

Stoica¹,

Epure

Sava³

et al. 2013

Microscopy Res & Technique

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The surface morphology of azo-polyimide films was investigated after 355 nm Nd: YAG laser irradiation with two different incident fluencies. Atomic force microscopy (AFM) was employed to correlate the laser-induced tridimensional nanogrooved surface relief with the incident fluence and the number of irradiation pulses. The height images revealed that the grooves depth increased even tens of times by increasing the incident fluence, using the same numbers of irradiation pulses. For low incident fluence, the films were uniformly patterned till 100 pulses of irradiation. Instead, when using higher fluence, after 15 pulses of irradiation the accuracy of the surface relief definition was reduced. This behavior could be explained by means of two different mechanisms, one that suppose the film photo-fluidization due to the cis-trans isomerization processes of the azo-groups and the second one responsible for the directional mass displacement. The dominant surface direction and parameters like isotropy, periodicity, and period were evaluated from the polar representation for texture analysis, revealing the appearance of ordered and directionated nanostructures for most of the experimental conditions. Also, the graphical studies of the functional volume parameters have evidenced the improvement of the relief structuration during surface nanostructuration. The correlation of these statistical texture parameters with the irradiation characteristics is important in controlling the alignment of either the liquid crystals or the cells/tissues on patterned azo-polyimide surfaces for optoelectronic devices and implantable biomaterials, respectively.

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An insight on the effect of rubbing textile fiber on morphology of some semi-alicyclic polyimides for liquid crystal orientation

Cited by 16 publications

References 40 publications

Insights on Light Dispersion in Semi‐Alicyclic Polyimide Alignment Layers to Reduce Optical Losses in Display Devices

Insights on Light Dispersion in Semi‐Alicyclic Polyimide Alignment Layers to Reduce Optical Losses in Display Devices

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

An atomic force microscopy statistical analysis of laser‐induced azo‐polyimide periodic tridimensional nanogrooves

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