Morphological effects on transparency and absorption edges of some semi-alicyclic polyimides

Barzic, Andreea Irina; Stoica, Iuliana; Fifere, Nicuşor; Vlad, Cristina Doina; Hulubei, Camelia

doi:10.1007/s10965-013-0130-8

Cited by 25 publications

(19 citation statements)

References 34 publications

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“…The transmittance of the free‐standing PI films was tested. In a previous work it was shown that poly(EPI/DDM) sample has a transmittance of 80% starting with 386 nm and in visible range increases to 89%. The cut‐off wavelength (λ c ), denoting the point where transmittance reaches 1%, is 307 nm.…”

Section: Resultsmentioning

confidence: 99%

“…Besides the optical features, the AL must exhibit a good ability to develop a uniform pattern after rubbing. Previous complex atomic force microscopy studies on poly(EPI/DDM) and other epiclon‐derived PI films showed that such materials exhibit a smooth surface with heights of the structural formations below 25 nm . Both investigated polymers exhibit flat and non‐porous surfaces with isotropic character ( Figure a,b).…”

Section: Resultsmentioning

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: Resultsmentioning

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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“…et al -eXPRESS Polymer Letters Vol.9, No.5 (2015) [456][457][458][459][460][461][462][463][464][465][466][467][468] 459 Figure 3. Absorption coefficient dependence on photon energy for the investigated polysilanes This approach has been also applied earlier for amorphous polymer foils [30][31][32]. The Tauc plots for the investigated polysilanes, displayed in Figure 4, present a saturation domain at high energies followed by an exponential one in the low energies range, from which were extracted the values of the optical band-gap energy (Table 2).…”

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confidence: 91%

The influence of polysilane chemical structure on optical properties, rubbed film morphology and LC alignment

Soroceanu¹,

Barzic²,

Stoica³

et al. 2015

Express Polym. Lett.

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Abstract. Polysilane films were prepared by the drop casting method and their optical and morphological properties have been analyzed in order to investigate their suitability as alignment layers for nematic molecules. The samples do not absorb the radiations in the visible domain, particularly those containing methylhydrosilyl units, and present a transmittance of about 90% starting from 390 to 1100 nm. The optical band-gap is higher than 3.26 eV for all polysilanes indicating a low probability of optical absorption processes in the visible range. The morphology of the pristine samples shows isotropically distributed granular formations. The polymer surface was oriented by rubbing with two types of velvet: one with short fibers and the other with long fibers. The latter generates higher surface anisotropy, as shown by the reduction of the surface texture direction index values. The presence of methylhydrosilyl units allows a denser packing of the polymer structure and thus finer surface periodicities, leading to better orientation of the nematic molecules on the polysilane surface.Keywords : material testing, polysilane, rubbing, morphology, LC alignment eXPRESS Polymer Letters Vol.9, No.5 (2015) 456-468 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2015.43 * Corresponding author, e-mail: irina_cosutchi@yahoo.com © BME-PT layer in the visible domain. The surface morphology of the rubbed alignment layer, the pretilt angle and surface energy of the alignment film are influenced by the conformation of the polymer molecular backbone [9]. Many studies are focused on preparing alignment layers by rubbing polyimides [10][11][12][13], poly(vinylidene fluoride) [14] or polyamides [15]. Since the absorption characteristics of alignment layer determines unwanted light-transmission modulation of the liquid crystal leading to ghost images on the LCD panel [16,17], the investigations are focused on transparent polymers with good surface alignment ability. Another class of transparent polymers is represented by polysilanes. They consist of chains exclusively made up of silicon atoms with significant delocalization of the sigma electrons along the backbone. This aspect leads to interesting electrical and optical properties, such as high quantum efficiency of charge generation, high charge-carrier mobility, efficient luminescence, and optical non-linearity [18]. Their photophysical properties are strongly influenced by the chemical structure of the polymer side groups and/or dimensionality of the skeletal framework [19,20]. To our knowledge there are no investigations on polysilane-based alignment layers patterned by rubbing. Previous papers [21][22][23] showed that polysilanes exhibit good ability of aligning molecules. The morphological features of these polymers are affected by UV exposure due to the scission of the main chain and oxidation processes [21]. Since UV-irradiated polysilane generated different orientation of nematic molecules from that induced non-irradiated polymer, pattern...

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“…To overcome these drawbacks, much effort has been devoted toward improving the processing characteristics of these relatively intractable yet promising polymers. These studies have included introducing flexible segments into the polymer backbone, replacing symmetrical aromatic rings with unsymmetrical ones, introducing bulky pendant groups, forming a noncoplanar structure, and introducing hyperbranched or substituted linear structures . These methods served to disrupt the crystallinity of these polymers, thus enhancing their solubility.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and properties of novel soluble poly(amide‐imide)s with different pendant substituents

Qian

Shi

et al. 2017

J. Polym. Sci. Part A: Polym. Chem.

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Two types of novel fluorinated diimide-diacid monomers-[2,2 0 -(4,4 0 -(3 0 -methylbiphenyl-2,5-diyl)bis(oxy)bis(3-(trifluoromethyl)-4,1-phenylene))bis(1,3-dioxoisoindoline-5-carboxylic acid)] (III) and [2,2 0 -(4,4 0 -(3 0 -(trifluoromethyl)biphenyl-2,5-diyl)bis(oxy)bis(3-(trifluoromethyl)-4,1-phenylene))bis(1,3dioxoisoindoline-5-carboxylic acid)] (IV)-were respectively designed and prepared by the condensation of diamines I and II with two molar equivalents of trimellitic anhydride. From both diimide-diacids, two series of novel poly(amide-imide)s (PAIs) (IIIa-IIIe and IVa-IVe) bearing different pendant groups were prepared by direct polymerization with various aromatic diamines (a-e). All the PAIs had a high glass transition temperatures (T g s, 232-265 8C), excellent thermal stability (exhibiting only 5% weight loss at 493-542 8C under nitrogen) and good solubility in various organic solvents due to the introduction of the bulky pendant groups. The cast films of these PAIs (80-90 lm) had good optical transparency (73-81% at 450 nm, 85-88% at 550 nm and 87-89% at 800 nm) and low dielectric constants (2.65-2.98 at 1 MHz). The spin-coated films of these PAIs presented a minimum birefringence value as low as 0.0077-0.0143 at 650 nm and low optical absorption at the near-infrared optical communication wavelengths of 1310 and 1550 nm.

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Morphological effects on transparency and absorption edges of some semi-alicyclic polyimides

Cited by 25 publications

References 34 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

The influence of polysilane chemical structure on optical properties, rubbed film morphology and LC alignment

Synthesis and properties of novel soluble poly(amide‐imide)s with different pendant substituents

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