Pursuing Phase Transitions of a Concentrated Polymer Solution by In Situ Fluorescence Measurements Based On Aggregation-Induced Emission

Abstract

Concentration-dependent phase transitions in concentrated solutions have remained speculation due to the serious impediment of macromolecule dynamics by intensive topological entanglement or intermolecular interaction as well as the absence of powerful tool for detecting changes in chain or segment movement. Herein, taking a general polymer, namely, poly(vinyl alcohol) (PVA), as an example, a water-soluble fluorescent molecule with aggregation-induced emission (AIE) is introduced into the PVA solutions as a chain dynamics indicator to investigate phase transitions at high concentrations through in situ monitoring of the solvent evaporation process. Two turning points of fluorescent intensity are observed for the first time at mean concentrations of ∼25% and ∼45%, corresponding to the gelation and amorphous-to-crystalline transitions, respectively. Our work offers a fundamental insight into the physical nature of concentrate-dependent nonequilibrium transitions and develops a reliable and sensitive approach based on the AIE phenomenon for following high-concentration-triggered property changes of a polymer solution.

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

“…However, when polymer chains are frozen, intramolecular motion of these rotors is restricted, hence nonradiative decay is suppressed, leading to significantly enhanced emission . It has been experimentally demonstrated in our previous work that TTVP molecules are highly sensitive to the chain motion of PVA in solution, exhibiting rapid response in fluorescence intensity change . Therefore, TTVP molecules are selected as a probe for the chain dynamics to study the film forming from PVA/plasticizer solutions in this work.…”

“…(1) The current study offers an integrated physical picture of condensed matter transition within a wide solution concentration range, especially the very late stage, glass transition, was unascertained in our earlier work. 34 (2) For the PVA/water system, the critical concentrations of skin-core delamination, gelation, and amorphous-to-crystalline transition are independent of solution initial concentration or PVA molecular weight. 34,45 However, all of the condensed matter structure transitions are influenced by the plasticizer content, indicating that the plasticizer plays a crucial role in the PVA film formation.…”

Inhibition of the Skin-Core Structure in Poly(Vinyl Alcohol) Films by Increasing the Diffusion-Induced Dominated Drying Process

“…33 The kinetic behavior of the amorphous is limited by the presence of crystalline domains above, and the dynamics gradient serves as a triggering factor for microstructural changes and the recording of polymer chains along the thickness direction. 34 Furthermore, Peclet number (Pe), 32 an important parameter for measuring heat transfer in fluid dynamics, can also be applied to the study of solution evaporation and film formation processes. During the solution drying process, evaporation and diffusion are two competing processes that have different effects on the solution uniformity.…”

“…This glass layer further hinders solvent evaporation within the solution system, thereby increasing the difference in concentration distribution in the thickness direction and eventually leading to the formation of a crystalline layer . The kinetic behavior of the amorphous is limited by the presence of crystalline domains above, and the dynamics gradient serves as a triggering factor for microstructural changes and the recording of polymer chains along the thickness direction . Furthermore, Peclet number ( Pe ), an important parameter for measuring heat transfer in fluid dynamics, can also be applied to the study of solution evaporation and film formation processes.…”

“…Additionally, NMR testing requires the use of deuterated reagents, which differ from actual aqueous solution systems and may not accurately reflect the segmental dynamics in real solution environments. In recent years, the laser-induced fluorescence (LIF) analysis technology has been widely applied in high-resolution imaging ,− due to its high spatial resolution and nondestructive optical sectioning capabilities. Babaie and Stoeber − used Rhodamine B dye as a fluorescent probe and studied the concentration field distribution during the deposition of PVA solutions through confocal microscopy imaging.…”