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

Abstract

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.

Semi-alicyclic polyimides as potential membrane oxygenators: Rheological implications on film processing, morphology and blood compatibility

“…The analyzed semialicyclic PIs were obtained by the polycondensation reaction between EPI dianhydride with either the DDM or 6FADE diamines in NMP medium (see Figure 1). The details concerning the synthesis procedure were described in a previous work [27]. Fourier transformed infrared spectra, previously published in [27], confirmed the studied polymer structures.…”

“…The details concerning the synthesis procedure were described in a previous work [27]. Fourier transformed infrared spectra, previously published in [27], confirmed the studied polymer structures.…”

“…% Table 5. The thermal and tensile properties of the studied PIs: glass transition temperature (T g -taken from reference [27]), initial decomposition temperature at which the sample displayed a 5% weight loss (IDT), the temperature corresponding to the loss of 10% by weight (T 10 ), the maximum decomposition temperature in the DTG curve (T d ), Young modulus, elongation at break (ε break ) and tensile strength (σ).…”

“…In the presented scientific context, this work brings new aspects concerning the processing and characterization of semi-aliphatic PIs for membrane oxygenator purposes. Two semi-alicyclic PI structures were prepared by polycondensation reaction using a similar procedure to that reported in other works [26,27]. For PI synthesis, EPI dianhydride was combined with two aromatic diamines (containing or lacking fluorine): 4,4′diaminodiphenylmethane (DDM) and 4,4′-(hexafluoroisopropylidene)bis(p-phenyleneoxy) dianiline (6FADE).…”

“…(3) development of new structure-properties relationships that will enable similar or improved performance relative to the reference one. In a previous paper, these polymers were studied from the point of view of their optical properties implication on the possibility to reduce losses in display devices [27]. Here, a special concern is ascribed to the correlation of the rheological behavior of PI solution in order to obtain proper films by tape casting.…”