Iodine-doped Polyvinyl Alcohol Research Articles

Drying temperature dependence of adhesion via H-bonds between polyvinyl alcohol and cellulose films

This study is to address the drying temperature dependence of the adhesion between an iodine-doped polyvinyl alcohol (PVA-Ix) and a saponified triacetyl cellulose (TAC) films, where a water-borne PVOH solution is used as an adhesive. Upon laminating three layers into a TAC/PVA-Ix/TAC sheet with two PVOH adhesive layers there between, drying process is carried out at temperature of 50, 60, 70, 80, and 90 °C, respectively. As a result, the adhesion (peel) strength initially increases with temperature, reaching a maximum at around 70 °C, and then decreases with further increasing temperature to 90 °C. We have interpreted this phenomenon by means of a physical model built to account for the competition between the kinetic and thermodynamic driving forces. In another words, there occurs competition in the drying process between the kinetic forces coupled with the water diffusion out of the system and the thermodynamic forces of the hydrogen-bond formation in the adhesion interfaces.

Polarization-dependent micro-structure fabrication with direct femtosecond laser writing on plastic polarizer films.

Iodine-doped polyvinyl alcohol (IDPVA) film has been widely used as a plastic polarizer due to its great linear dichroism. We found that the anisotropic character of the plastic polarizer can be permanently damaged upon exposure of high intensity femtosecond laser pulses. This process is a two-photon-induced chemical reaction and denominated as two-photon-induced isotropy (TPII). The TPII effect can form a high polarization contrast on the base of the original IDPVA films. With this property, polarization-sensitive diffractive optical elements are fabricated in IDPVA films. The low cost of the IDPVA film and the high polarization contrast of TPII make it a promising new candidate for femtosecond laser fabrication of polarization-selective optical elements.

Enhancing mechanical properties of gel‐spun polyvinyl alcohol fibers by iodine doping

AbstractHigh strength polyvinyl alcohol (PVA) fibers with a conventional degree of polymerization of 1500 were prepared by doping iodine with PVA spinning solution. The iodine‐doped PVA (I‐PVA) aqueous solution was extruded into cold methanol that provides dark purple PVA‐iodine complex gel fibers. Only a small amount of iodine was required to enhance drawability and molecular orientation by reducing the interaction between PVA chains. An increase of ca. 10% in the maximum draw ratio of the doped fibers compared with that of undoped PVA translated into values for the tensile strength, 2.2 Giga‐Pascal (GPa), and initial modulus (47 GPa) that were more than 30% higher than those of the neat PVA fiber. Easier chain slippage of molecules in the amorphous segments of the I‐PVA fiber during drawing leads to increased orientation in these segments, which is believed to be the source of the improvements in mechanical properties. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

Multiple scattering approach to I K-edge XANES for iodine-doped PVA films

Polarization dependent iodine K-edge XANES spectra of iodine-doped polyvinyl alcohol (PVA) films provide much information on the local structure around iodine anion. The present multiple scattering analyses support that the iodide anions are along to the PVA chain in the films. The difference XANES spectra taken between 0° and 90° and between 45° and 90° are slightly sensitive to the local structure of the PVA film around iodine anions.

Iodine-doped polyvinylalcohol using positron annihilation spectroscopy

Iodine-doped polyvinylalcohol, doped up to 52 wt %, was studied using positron annihilation lifetime technique and Doppler broadening of annihilation radiation. Three component, free fit analysis was used for the lifetime spectra. It is found that ${I}_{3}$ drops sharply on initial iodine doping, whereas decrease in ${\ensuremath{\tau}}_{3}$ is small, indicating inhibition of positronium formation by the dopant. The S parameter, on iodine doping, initially shows a drastic increase due to the decrease in crystallinity of the doped sample. Differential scanning calorimetry (DSC) and x-ray diffraction curves confirm that doping results in decreased crystallinity of the sample. ${\ensuremath{\tau}}_{3}$ increases beyond 23 wt % doping level due to structural changes induced by formation of polyiodide complexes, which is confirmed by UV-Vis spectra, for moderately and highly doped samples. The drop in ${\ensuremath{\tau}}_{3}$ at higher levels of doping (g44 wt %) suggests chemical quenching of positronium, probably due to iodine aggregation. DSC confirms formation of iodine aggregates, as revealed by a large endotherm at $185\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ for doping levels beyond 47 wt %.

Polaroid H-sheet as a polarizer for 33 keV X-rays

It is shown that Polaroid H-sheet (iodine-doped polyvinyl alcohol) can be used to good effect as a fixed-wavelength polarizer for 33.17 keV X-ray beams. Iodine K-edge dichroic spectra of HN22 and HN38 sheets are presented, and the HN22 is used to demonstrate X-ray polarization analysis and polarization rotation.

Structure, Composition, and Vibrational Property of Iodine-Doped Polyvinyl Alcohol Studied by Temperature-Dependent I K-Edge Extended X-Ray-Absorption Fine Structure

Abstract The temperature dependence of the I K-edge extended X-ray absorption fine-structure (EXAFS) spectra of a highly oriented iodine-containing polyvinyl alcohol (I-PVA) film was investigated in order to reveal any local structures around I. It was firstly demonstrated that an analysis of the EXAFS amplitude, which is associated with the Debye–Waller factor (mean square relative displacement) provides information concerning the composition ratio of the dopant species. In the present high-contrast I–PVA film it was found that a significant amount (64%) of isolated I− is present, and that the polyiodine species, which contributes to a high polarization property of I–PVA for ultraviolet and visible light, consists of 21% I3− and 15% I5−, without containing neutral I2.

129I and125Te Mössbauer studies of polyvinyl alcohol films doped with iodine

129I and125Te Mossbauer measurements have been performed on unidirectionally stretched iodine-doped polyvinyl alcohol (PVA) films which are widely used as optical polarizers. From the129I measurements iodine is observed to be in the form of linear polyiodides, I3− and I5−, lying parallel to the stretch direction of the PVA films. From the125I emission Mossbauer measurements the structural arrangement of the iodine-PVA complex is also discussed.

Mössbauer Spectroscopic Study of Iodine-Doped Polyvinyl-Alcohol Films

Iodine-doped polyvinyl-alcohol(PVA) films were studied at 16 K using the Mossbauer resonance of 129 I. Experiments were done for the PVA films with or without boric acid, stretched or not, and doped with iodine only or co-doped with iodine and bromine. For the iodine-doped PVA films without boric acid, a major iodine species is I - . The addition of boric acid causes the formation of linear polyiodides with symmetrical charge population, I 3 - and I 5 - , and the stretch of the films increases the abundance ratio of I 5 - . From the analysis of the intensity ratio of the quadrupole split lines, it was confirmed that the linear polyiodides, I 3 - and I 5 - , lie parallel to the stretching direction. For iodine and bromine co-doped stretched films with boric acid iodine exists as the central ion in the form of linear IBr 2 - .

Light polarization in iodine-doped polyvinyl alcohol films

129I Mossbauer measurements have been performed on unidirectionally stretched iodinedoped polyvinyl alcohol(PVA) films which are widely used as optical polarizers. In the films iodine is observed to be in the form of I−, I 3 − , and I 5 − and the stretch of the films increases the abundance of the polyiodides, I 3 − and I 5 − . In the stretched PVA films, it has become clear that the linear polyiodides lie parallel to the stretching direction.

Selective resonant Raman enhancement in polyiodide chains

A selective resonant Raman enhancement is observed in solid films of the blue complex formed between starch and iodine. The intensity of the 162-${\mathrm{cm}}^{\ensuremath{-}1}$ phonon peak is strongly enhanced when the laser frequency is resonant with the main electronic absorption band at \ensuremath{\simeq} 590 nm, whereas the 112-${\mathrm{cm}}^{\ensuremath{-}1}$ phonon is strongly enhanced when the laser frequency is tuned in the blue region in resonance with the shoulder at \ensuremath{\simeq} 455 nm. Similar behavior has been observed in a number of compounds containing polyiodide chains such as iodinedoped polyvinyl alcohol, sulfur polynitride, and polyacetylene. A theoretical explanation of this phenomenon is given in terms of the theory of resonant secondary emission, and explicit analytical expressions for the Raman cross sections as a function of the exciting wavelength are derived for the case of resonance with broad and structureless absorption bands (i.e., a rapidly relaxing system with strong electron-vibration interactions). A structural model for the chromophore of these compounds is also proposed.