Dichroic Ratio Measurements Research Articles

Ultrathin Polythiophene Films Prepared by Vertical Phase Separation for Highly Stretchable Organic Field‐Effect Transistors

AbstractPhysically blending semiconducting conjugated polymers with elastomeric materials and precisely controlling the resulting film structure provides an effective strategy to obtain intrinsically stretchable semiconducting polymers. Here, vertically phase‐separated ultrathin poly(3‐hexylthiophene) (P3HT) and polystyrene‐b‐polyisoprene‐b‐polystyrene (SIS) blend films are developed for one‐step fabrication of semiconductor and insulator layers of organic field effect transistors (OFETs). The phase‐separated structure, surface morphology, and tensile deformation are characterized by UV–vis absorption spectroscopy, atomic force microscopy, and optical microscopy. The blend film device maintains 43% of its mobility compared with 0.1% mobility of the pristine P3HT films after 50% stretch. The deformability of the films is efficiently improved by blending proved by both the finite element analysis and the dichroic ratio measurements. The P3HT/SIS blended films possess reproducible properties under 200 continuous stretch–release cycles at a strain of 50% without significantly reduced mobilities. The fully‐stretchable OFETs on polydimethylsiloxane substrate are also investigated and show a stretchability up to 70% and good electrical recovery properties after stretch–release process. The vertical phase‐separated structure obtained by the blends provides an effective way to easily fabricate stretchable devices with a balance between their mechanical and electrical properties.

Real‐time orientation and crystallinity measurements during the isotactic polypropylene film‐casting process

AbstractA method based on Fourier transform infrared (FTIR) transmission spectra is proposed to measure the crystallinity of isotactic polypropylene (iPP) samples. The method parameters were tuned as compared with wide‐angle X‐ray scattering measurements performed on test samples characterized by different crystallinity values obtained by solidification of thin iPP films under several cooling rates in a homemade device. The FTIR dichroic ratio measurements were adopted to measure crystalline and average Hermans' orientation factors of iPP samples obtained by film casting. The crystalline orientation measurement method was validated as compared with the birefringence measurement. The techniques were successfully used in real time during some film‐casting runs with a suitably modified FTIR system made of a spectrometer equipped with two optical guidelines and an external detector. Real‐time measurements are reported and discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 998–1008, 2003

FTIR Investigation of the Molecular Structure at the Crack Interface in Unfilled and Silica Filled Polyisoprene

Unfilled and silica-filled polyisoprene samples were stretched until cracking was initiated. The crack interface was then studied using Fourier transform infrared (FTIR) microspectroscopy to investigate the changes in the molecular structure induced by crack formation. Unfilled rubber samples had a constant absorbance for all molecular frequencies in all regions surrounding the crack tip at the resolution of the FTIR microscope. Silica filled samples, however, had a higher absorbance of the C=C stretching frequency in the area immediately ahead of the crack tip. The high absorbance region corresponds to the region of highest stress in crack tip stress analysis. Dichroic ratio measurements were performed to investigate the relationship between orientation and stress. Results showed a higher dichroism of the C=C frequency immediately ahead of the crack tip. Differential scanning calorimetry experiments were performed to determine the crystallinity of the rubber after it was stretched. No residual crystallinity was found as a result of the stretching procedure. The temperatures necessary for the microtoming process also did not produce any residual crystallinity.

Effect of Chemical Structures of Polyimides on Unidirectional Liquid Crystal Alignment using a Single Linearly Polarized UV Exposure

Unidirectional liquid crystal (LC) alignment by a linearly polarized UV exposure was examined using various polyimides (PIs) which consist of different tetracarboxylic dianhydrides and diamines. Measurement of dichroic ratios of LC cells suggests that sensitivity of unidirectional LC alignment for UV dosage is largely affected by the chemical structures of PIs used. The results of dichroic ratio measurement of LC cells, UV absorption spectra, birefringences, FT-IR spectra of PI films, and molecular conformations of diamines in Pis calculations using molecular mechanics suggest that the selective photo-decomposition of PI caused the anisotropic van der Waals forces which aligns the LC along its optic axis in residual PI chain.

Regularity and Narrowness of the Intervals of the Microgrooves on the Rubbed Polymer Surfaces for Liquid Crystal Alignment

It has been proved that genuine microgrooves on the rubbed polymer surfaces for liquid crystal alignment have very regular and narrow intervals. The minimum mean interval, 0.03 μm, is observed by field-emission scanning electron microscope (FE-SEM) after staining the polyimide alignment layer with ruthenium tetroxide (RuO4) at room temperature. Its coefficient of variance is 14.7%. Results on Atomic Force Microscope (AFM) measurements essentially coincide with that of FE-SEM. On the other hand, microgrooves of the poly(amic acid) which has poor ability to let the liquid crystals align, have less regular and wider intervals than polyimide. Five other polymers were also observed in the same manner. Non-destructive staining at room temperature and the existence of heavy metal compound on and just beneath the surface may make possible observation of the real topography of the rubbed polyimide surface. It is also emphasized from dichroic ratio measurements that observation without any distortion of the samples is very important.

The role of benzotriazole in corrosion inhibition: formation of an oriented monolayer on Cu 2O

Studies of the adsorption of benzotriazole (BTAH) on Cu 2O surfaces have been carried out up to saturation coverage using both experimental (transmission UV and Auger electron spectroscopy (AES)) and computational approaches. Correlation of the UV integrated band intensity for the adsorbed BTA − species with quantitative measurements of N/Cu ratios from AES shows the saturation coverage of chemisorbed BTA − to be Γ ML ≈ 6.3 × 10 14 cm −2. Calculations based on a molecular mechanics (MM2) minimization of the BTA − structure show a maximum surface density of 8.3 × 10 14 and 2.4 × 10 14 cm −2 for orientations in which the BTA − plane is perpendicular and parallel to the surface, respectively, thereby indicating that BTA − cannot be bound with the ring plane parallel to the surface under these conditions. Furthermore, the orientation is invariant with surface density, as demonstrated by coverage-dependent dichroic ratio measurements. Semi-empirical calculations of free BTA − and transmission linear dichroism measurements suggest that an orientation in which the ring plane is perpendicular to the surface with the C 2 axis canted away from the surface normal is the most reasonable proposal for the structure of the adsorbed layer.

Corrections for polarizer and spectrometer imperfections in the measurement of infrared dichronic ratios

Abstract The measurement of dichroic ratios in highly absorbing systems requires careful consideration of the effects of instrumental polarization sensitivity and of polarizer imperfections if accurate results are to be obtained. If the absorbances exceed about 1.5, corrections due to imperfect polarizers can become important but are fairly easily performed. With the polarizers set in the standard 45° geometry, the correction due to instrumental polarization sensitivity is small.

Molecular organization of DNA in chromosomes.

AbstractMetaphase chromosomes of Chinese hamster and lampbrush chromosomes of Triturus viridescens were studied for DNA arrangement by polarized fluorescence microscopy and by linear dichroic ratio measurements. Intact chromosomes showed a small but negative polarization (−8%) of fluorescence, while the dichroic ratio was negative and quite appreciable (0.85). On treatment with trypsin or RNase the polarization value increased to about −34% with no change in the polarization direction. The dichroic ratio on the other hand remained unchanged on such enzyme treatments. These results, along with the data of form dichroism and the change in fluorescence color following any enzyme action, suggest that basically the preexisting DNA arrangement was revealed by these enzymes. The fully enzyme‐treated chromosome–dye complexes showed cross‐bands. Quantitatively, the highest degree of DNA orientation across the above two chromosomes was in the range of 15–34%. This orientation fits well with a coiled coil‐DNA, which is mostly longitudinal in these chromosomes. It is suggested that this longitudinal coil may have occasional defects in DNA structure. Alternatively, this coil may terminate into regions of random DNA and unsupercoiled DNA showing lateral projections, such as loops. This alternating feature of the DNA arrangement would tandemly repeat in either metaphase and lampbrush chromosomes.

Dichroic Ratio Measurements in the Infrared Region

An analysis of conventional optical arrangements for the measurement of dichroic ratios in the infrared region reveals that such measurements may be in error by factors up to 3 or more. These errors result from failing to account for the effects of prism polarization and of the imperfection of polarization in the transmitted beam of multiple plate AgCl polarizers. Elimination of the effect of prism polarization by a method proposed by Elliot, Ambrose, and Temple is shown to be relatively ineffectual when a transmission polarizer is employed. The magnitude of the error varies with the true dichroic ratio and with the optical density of the sample for polarized radiation parallel to one of the optic axes. A frequency dependent parameter is found to account for relatively isotropic intensity losses resulting from absorption and scattering by the AgCl in the polarizers; observed values of this parameter are given for three wavelengths, 1.67μ, 3.85μ, and 4.80μ.