X-ray diffraction: X-ray diffraction is a common method to analyze the crystal structure of polymers. Through the X-ray diffraction analysis of polymer samples, the crystal structure information of polymer can be obtained, and then the folding of polymer chain in crystal region can be determined.
2. Thermal analysis: the structure of polymer samples will change during heating, so the folding of polymer chains in crystal region can be studied by thermal analysis technology. For example, differential thermal analysis (DSC) can measure the thermal stability, melting point, glass transition temperature and other information of polymer samples, which can reflect the arrangement and folding of polymer chains in the crystal region.
3. Nuclear Magnetic Resonance (NMR): NMR can analyze the structure and folding of polymer chain by detecting hydrogen atoms at different positions on the polymer chain. For example, the three-dimensional structure information of polymer chains can be obtained by using two-dimensional nuclear magnetic resonance technology, so as to determine the folding situation of polymer chains in the crystal region.
4. In-situ stretching: In-situ stretching can be used to study the folding of polymer chains in crystal regions by stretching polymer samples and simultaneously performing X-ray diffraction analysis. Through different stretching conditions and angles, we can get different folding States of polymer chains in the crystal region, so as to further understand the structure and properties of polymer chains.
Prospect of theoretical model of polymer crystallization;
The theory of polymer crystallization is a big difficulty and challenge in polymer science. In the past century, scholars have put forward many different theoretical models to understand and solve the basic scientific problems of polymer crystal nucleation and growth. However, due to the complexity and diversity of the polymer system itself, so far, there is no theoretical model that can completely describe the process and characteristics of polymer crystallization.
Professor Li from the National Synchrotron Radiation Laboratory of China University of Science and Technology published a paper entitled "The Difficult Course of Polymer Crystallization: Hitting with Chain Flexibility and Connectivity" [Macromolecule 2019,52,3575? 359 1], Ph.D. student Tang and associate researcher Chen Wei are the first authors of the paper.
This prospect aims to raise questions and stimulate discussion. Firstly, classical nucleation theory and non-classical nucleation theory are introduced, and the characteristics, basic assumptions and shortcomings of these important theoretical models are summarized. On this basis, this paper reviews the Hoffmann-Lauritzen model of polymer crystallization and the multi-stage model proposed by Professor strobl, as well as the debate between the two models. In addition, the prospect also introduces the "two-step nucleation" theory developed in protein, colloidal particles and other fields in recent years, thus emphasizing the existence of intermediate state in polymer crystallization and its important role in crystallization.