Investigating polymer crystallization at the nanoscale using AFM-IR

控制聚合物和复合材料的形态和结晶是至关重要的，因为它直接关系到材料的最终性能。半结晶聚合物是商用聚合物的重要组成部分。众所周知，混相聚合物共混物可以具有多种形态和结晶机制，这取决于各组分的熔融温度、共混物组成和结晶条件的差异。这些现象在可混溶和可结晶聚合物的二元共混体系中变得更加复杂，其中两种组分相互竞争以达到最终结构（例如形状、取向、形态、形貌、质地和密度）。然而，尽管物理化学表征方法取得了进展，但检测聚合物在可结晶聚合物共混物中的分布，特别是在亚微米尺度上的分布，在技术上是困难的。最近，我们已经能够使用先进的设备，即原子力显微镜-红外光谱（AFM-IR），研究聚合物在混相和非混相共混物中的结晶和纳米扩散，同时在纳米尺度上记录它们的高分辨率地形图像。这一进步是通过AFM-IR定性鉴定化合物的化学成分的能力而成为可能的。初步结果已经发表了几篇文章并获得了一些奖项。在这个研究项目中，我们将开发新的方法来更好地理解生物可降解聚合物的混相、结晶和分布，特别是在纳米级的二元聚合物共混物，主要使用原子力显微镜结合红外光谱（AFM-IR）或热电偶（Nano-TA）。为了了解结晶过程中的分子结构，将对聚合物共混物进行动力学模拟，主要使用专门用于聚合物和生物分子的大规模原子/分子大规模平行模拟器（LAMMPS）分子动力学模拟器软件。纳米尺度表征方法有助于更好地回答文献中的开放性问题，特别是分子排列，片层发育机制，球形结构中的形态和相变，这些是检测生物聚合物材料最终行为的更重要特征。了解聚合物的扩散与球粒结构的关系以及聚合物共混物的操作条件将提供重要的科学贡献，并为三元和四元共混物等复杂体系的结晶研究开辟新的途径。改善聚合物共混物的性能将扩大这些生物聚合物在生物医学材料和生物组织等各种应用中的使用领域（2019年全球市场规模为254亿美元）。

Controlling the morphology and crystallization of polymers and composites is crucial because it is directly related to the final properties of the material. Semi-crystalline polymers are an important fraction of commercial polymers. It is well known that miscible polymeric blends can have a variety of morphologies and crystallization mechanisms that depend on the difference in the melting temperature of each component, the blend composition and the crystallization conditions. These phenomena become more complex in the binary blends of miscible and crystallizable polymers where the two components are in competition to reach the final structure (e.g. shape, orientation, morphology, topography, texture and density). However, the examination of the distribution of polymers in crystallizable polymer blends, especially at the submicron scale, is technically difficult despite the progress of the physicochemical characterization methods. Recently, we have been able to use an advanced equipment, i.e. atomic force microscopy-infrared spectroscopy (AFM-IR), to study the crystallization and nano-diffusion of polymers in miscible and immiscible blends, while recording their high-resolution topographic images at the nanoscale level. This advancement was made possible through the ability to qualitatively identify the chemical composition of the compound through AFM-IR. The preliminary results have led to several publications and awards. In this research program, we will develop new approaches to better understand the miscibility, crystallization and distribution of biodegradable polymers, particularly the binary polymeric blends at the nanoscale level using mainly atomic force microscopy coupled with an infrared spectroscopy (AFM-IR) or a thermocouple (Nano-TA). The simulation of the dynamics of the polymer blends will be carried out in order to understand the molecular structure during the crystallization using mainly the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) Molecular Dynamics Simulator software dedicated to polymers and biomolecules. Nanoscale characterization methods help to better answer the open questions in the literature, particularly the molecular arrangements, lamella development mechanisms, morphology and phase transition in a spherical structure that are more important features to detect the final behavior of biopolymer materials. Understanding the diffusion of polymers in relation to the structure of spherulites and the operating conditions in polymer blends will provide an important scientific contribution and open a new pathway for crystallization studies in complex systems, such as ternary and quaternary blends. Improving the properties of the polymer blends will extend the field of use of these biopolymers in various applications such as in biomedical materials and biological tissues (globally, market of US$25.4 billion for 2019).