Effect of boric acid treatment method on the characteristics of poly(vinyl alcohol)/iodine polarizing film

Abstract

Four types of polyvinyl alcohol (PVA)/iodine complex films were made using different boric acid treatments to prepare polarizing films having high durability under humid and warm atmospheres and to identify the effects of the boric acid treatment method on the formation of the PVA/iodine polarizing film. The four types of films were a PVA iodinated film(I), a PVA film that was iodinated and then treated with boric acid(I-B), a PVA film that was treated with boric acid and then iodinated(B-I), and a PVA film that was simultaneously treated with iodine and boric acid(IþB). The concentrations of I 2 /KI were 0.03, 0.05, and 0.07 mol/L, and the concentrations of boric acid were 0.1, 0.3, and 0.5 mol/L. Comparing four type films treated with 0.05 mol/L I 2 /KI and 0.5 mol/L boric acid, the conformation of PVA/iodine complexes for I-B film were larger than the others. The degrees of polarization (q) of all of the films increased to very high levels (99.9%:). The durability of I-B was superior to B-I or IþB, and the change in the q was below 5% because the boric acid treated after iodine treatment reduced the molecular mobility of the PVA/ iodine complex chains through intracrosslinking, so that the PVA/iodine complex could not easily collapse.

Molecular iodine/polymer complexes

“…High amounts of solvents such as acetone, DMF, methanol, ethanol, pyridine, or formic acid, will destroy the complex and the color will fade. Shin et al [173,174] reported the use of boric acid treatment to form I 2 PVA polarizing film characterized by its transmittance and polarization degree. The acid promoted the formation of iodide species I 3¯ and I 5¯, and improved the durability of the film under heat and humidity.…”

Formation and dichroism of poly(vinyl alcohol)–iodine complex in photocurable film

“…Figure a–c shows and compares the UV–visible absorption spectra of PVA‐SbQ films (P‐I) and PVA‐SbQ films (P‐I‐B) of a) MQ2011, b) MQ2012 and c) MQ2013. In these spectra, absorption bands at 200, 290, 360, 470 and 600 nm are identified as being derived from I − , I 3 − , free I 2 I 3 − , PVA–I 3 − and PVA–I 5 − complex . We can see the presence of I − , I 3 − and free I 2 I 3 − in the films (P‐I) in Fig.…”

“…The complexes and structures of polyiodines with poly(vinyl alcohol) (PVA) and other polymers have been studied and discussed for many years, and have been applied to polarizer films for actual use, such as being used as an important component of liquid crystal displays. Aggregation models for PVA–I 3 − and PVA–I 5 − complexes have been suggested, which are enveloped by four PVA segments of syndiotactic configuration with extended conformation .…”

“…Boric acid forms crosslinked bonding in PVA, and it stabilizes PVA–polyiodine complexes in the polymer. The effects of boric acid on PVA–polyiodine complexes and the reactions have been studied, and a mechanism has been proposed …”

Effect of dye structure on orientational behavior and transition dipole moments in coatable guest–host polarizers

“…Nowadays, the maximum demand for polarizers is in the area of liquid crystal displays (LCDs). PVA-iodine polarizing films, which exhibit the highest polarization efficiency among commercial polarizers, are mainly used in this area [1][2][3]. However, PVA-based polarizing films should be protected by tri-acetyl cellulose (TAC) because of their low stability.…”