Crystallization Behavior of Semicrystalline Polymers Characterized by an In Situ Fluorescence Technique and its Sensing Mechanism

Abstract

In this study, fluorescence spectroscopy is used to study the bulk nonisothermal and isothermal crystallization of poly(L‐lactic acid) (PLLA) by monitoring in situ the temperature (T)‐ and time (t)‐dependent fluorescence intensity of the fluorophores incorporated into the PLLA matrix, respectively. The crystallization behavior characterized by fluorescence resemble those measured by conventional differential scanning calorimetry, confirming the validity of this fluorescence technique for sensing crystallization. Combined in‐situ fluorescence results and ex‐situ X‐ray diffraction characterizations demonstrate that this fluorescence technique shows great sensitivity not only to the degree of crystallinity but also to the crystalline microstructures formed during crystallization (e.g., α versus α' form PLLA crystals). Moreover, complementary fluorescence microscopy to this technique help reveal the intrinsic crystallization sensing mechanism: As crystals form during crystallization, the bulky fluorescent probes excluded from the crystalline regions reside in the rigid/mobile amorphous (i.e., non‐crystalline) regions of the resulting semicrystalline matrix, and their intramolecular motions are restricted by the neighboring crystalline domains and thus their fluorescence intensity is greatly enhanced upon crystallization. Because of its high sensitivity, fluorescence is powerful for studying the crystallization behavior of ultrathin polymer films (e.g., 75 nm) and elucidating confinement and interfacial effects through future studies.This article is protected by copyright. All rights reserved

Unveiling the Nanoconfinement Effect on Crystallization of Semicrystalline Polymers Using Coarse-Grained Molecular Dynamics Simulations

“…A fundamental understanding of the complex polymer crystallization affected by intrinsic and extrinsic factors can help to improve control over the properties of semicrystalline polymers and lead to novel inverse designs of polymer materials. The crystallization behavior of semicrystalline polymers is a classical problem of polymer physics research and is of great technological and scientific importance [ 4 , 5 , 6 ].…”