Effects of Plasticizers on Structural Transitions and Heterogeneity of Poly(vinyl alcohol) Films as Studied via AIE Materials

Abstract

Solution casting is a common processing method in industrial production. The phase-structure transitions driven by solvent evaporation directly impact the quality of the final film. However, due to the presence of solvents and other additives in the solution, it is difficult to detect the condensed matter structure during the drying process. This work studies structural transitions and heterogeneity of a poly­(vinyl alcohol) (PVA) film during water evaporation using glycerol as a plasticizer. Aggregation-induced emission (AIE) molecules are utilized to indicate the change in PVA chain dynamics during evaporation. The gelation, crystallization, and glass transition can be clearly detected via emission intensity change of the AIE molecules during water evaporation. It is found that the critical concentrations triggering structural transitions increase with the glycerol content, attributed to the release of PVA segmental mobility by the plasticizer. Furthermore, structural uniformity in the thickness direction is realized while the PVA film was loaded with 20% glycerol. It is revealed that glycerol diminishing the heterogeneity is due to the dual effect of hydrophilic glycerol reducing the evaporation rate and enhancing diffusion. Finally, the mechanism of the plasticizer in delaying structural transitions and ameliorating the heterogeneity in PVA films is discussed, which could provide theoretical guidance for preparation of polymer films via solution casting.

Supercooling and Solvent Depletion-Driven Poly(vinyl Alcohol) Film Formation Mechanism as Elucidated by In Situ Synchrotron Radiation X-Ray Scattering

“…Various polymer film products, i.e. , poly­(vinyl alcohol) (PVA) base films for producing polarizers used in thin-film-transistor liquid–crystal display and organic light-emitting diode and microporous polyolefin films for lithium batteries, are produced by such wet processes. − After being cast onto the roll-to-roll manufacturing line, the polymer film experiences notable microstructure evolution during the drying process. Despite numerous investigations related to the amorphous polymer film formation during drying, reports related to the microstructure evolution of semicrystalline polymer are quite limited. − Compared with the amorphous polymer film, the film formation of the semicrystalline polymer during drying needs to consider more phase transitions, i.e.…”

Suppression of the Skin-Core Structure of Poly(vinyl alcohol) Films by Adding Urea/Diethanolamine to Improve the Mechanical and Optical Properties

“…PVA-based films are processed by solution casting, , a method in which the primary mechanism driving structural transformation is the volatilization and diffusion of solvent molecules. − On the one hand, the volatilization rate at the solution–air interface differs from that at the solution–substrate interface. On the other hand, PVA is a semicrystalline polymer, , and the evaporation of the solvent during film formation will promote the development of both crystalline and amorphous (glassy) phases .…”