非溶劑誘導相分離形成膜和膠囊的微觀結構動力學

Abstract

高分子薄膜和膠囊被廣泛應用於各種工業和日常應用中。瞭解它們的動力學、形態和微結構可以為工程、科學和製藥領域提供有價值的見解。本篇論文主要分為四個部分，深入探討了使用非溶劑誘導相分離方法所產生的高分子薄膜和膠囊的固化動力學機制。 (1) 非溶劑誘導相分離是高分子薄膜製作中常見的技術，涉及液-液分離。利用分子模擬來研究薄膜形成動力學，追蹤膜收縮和各物質濃度的分布。可區分三個不同的區域：界面區域、致密層和中間區域，且這三個區域的固化機制各不相同。模擬結果顯示相分離是由溶劑萃取和高分子增濃所引起的，而不是非溶劑誘導引發。這些結果顯示由於溶劑損失和過飽和而導致的定向固化以及薄膜自動分層化。此篇研究成果已被刊登於Journal of Membrane Science期刊：Hu, H.-W., et al. (2023). “Solidification dynamics of polymer membrane by solvent extraction: Spontaneous stratification.” Journal of Membrane Science 683: 121846。 (2) 利用模擬探索非溶劑誘導相分離生成高分子薄膜的過程，並對其固化機制加以研究。主要探討非溶劑和溶劑之間的親和力對薄膜形態和微結構的影響。強親和力導致主動交換和形成穿越孔洞的結構；而弱親和力則導致由於溶劑損失過飽和而形成封閉的空隙結構。再者，模擬結果發現薄膜微結構與高分子構形相關，這些高分子在薄膜中呈現低結晶度和具有較小的尺寸的捲曲螺旋狀態。推測若選用強親和力的非溶劑和溶劑會導致固化加速，並且降低整體薄膜的結晶度以及高分子的排列。此篇研究成果已被接受於Macromolecules期刊：Hu, H.-W., et al. (2024). “Impact of Nonsolvent-Solvent Affinity on Membrane Morphology and Microstructure: Unraveling the Transition from Traversing Pore to Closed Void Structures.” Macromolecules 57(15): 7640-7653。 (3) 利用耗散性粒子動力學模擬研究高分子溶液微滴在非溶劑浴中固化成膠囊和微粒的過程，並且探索了各種初始高分子濃度下的過程。分析了收縮微滴的動力學、溶劑和非溶劑濃度以及高分子濃度分布。研究結果顯示，初始高分子濃度顯著影響宏觀形態和微觀結構：較高初始濃度導致形成具有較長尺寸的高分子殼的中空微粒，而較低初始濃度則產生具有增加的摺疊鏈的固體微粒。此篇研究成果已被刊登於Macromolecules期刊：Hu, H.-W., et al. (2024). “Nonsolvent-Induced Solidification of Droplets of a Polymer Solution: From a Sphere to a Capsule.” Macromolecules 57(3): 847-857。 (4) 在非溶劑浴中固化二元高分子溶液液滴可創建獨特的微載體。我們使用耗散粒子動力學模擬，探索了含有兩種不相容高分子的沉澱物的形態。最終結構取決於高分子間的不相容性、高分子與非溶劑的不相容性以及莫爾分率。當高分子間不相容性較低時，形成多相高分子殼層；而當其較高時，則形成異質雙面顆粒。增加聚合物與非溶劑的不相容性，會使微膠囊殼從多相轉變為雙層。

Polymer membranes and capsules find widespread use in various industrial and everyday applications. Understanding their dynamics, morphologies, and microstructures can yield valuable insights for engineering, scientific, and pharmaceutical purposes. The dissertation is divided into four major parts, delving into the solidification dynamics mechanisms of polymer membranes and capsules using the nonsolvent-induced phase separation method. (1) Nonsolvent-induced phase separation is a common technique in polymer membrane creation, involving liquid-liquid separation. Simulations are utilized to investigate membrane formation dynamics, tracking film shrinkage and concentration profiles. Three distinct regions are identified: the interfacial region, dense layer, and middle region. Demixing arises from solvent extraction and polymer concentration, rather than nonsolvent-induced separation. These findings shed light on directional solidification and membrane stratification due to solvent loss and oversaturation. This research has been published in the journal: Hu, H.-W., et al. (2023). “Solidification dynamics of polymer membrane by solvent extraction: Spontaneous stratification.” Journal of Membrane Science 683: 121846. (2) Simulations are employed to explore how nonsolvent-induced phase separation generates polymer membranes and elucidates their solidification mechanisms. The impact of the affinity between nonsolvent and solvent on membrane morphology and microstructure is examined. Strong affinity results in active exchange and the formation of traversing pore structures, whereas weak affinity leads to closed void structures due to solvent loss oversaturation. Membrane microstructure correlates with polymer conformations, with polymers in smaller size observed in membranes with low crystallite content and coil-like conformations. Strong affinity accelerates solidification, reducing crystallinity and polymer alignment. This research has been published in the journal: Hu, H.-W., et al. (2024). “Impact of Nonsolvent-Solvent Affinity on Membrane Morphology and Microstructure: Unraveling the Transition from Traversing Pore to Closed Void Structures.” Macromolecules. (3) Investigating the solidification of polymer solution droplets into capsules and particles in a nonsolvent bath, the research employs dissipative particle dynamics simulations to explore this process across various initial polymer concentrations. It analyzes the dynamics of shrinking droplets, solvent and nonsolvent concentrations, and polymer concentration profiles. Results indicate that initial polymer concentrations significantly impact both macroscopic morphology and microscopic configuration: higher concentrations lead to hollow particles with longer polymer shells, while lower concentrations produce solid particles with increased chain-folding. This research has been published in the journal: Hu, H.-W., et al. (2024). “Nonsolvent-Induced Solidification of Droplets of a Polymer Solution: From a Sphere to a Capsule.” Macromolecules 57(3): 847-857. (4) Solidifying binary polymer solution droplets in a nonsolvent bath creates unique microcarriers. Using dissipative particle dynamics simulations, we explored the morphologies of precipitates with two immiscible polymers. The structure depends on inter-polymer and polymer-nonsolvent incompatibility and mole fraction. Multi-compartment shells form when inter-polymer incompatibility is lower, while Janus particles form when it is higher. Increasing polymer-nonsolvent incompatibility changes the microcapsule shell from multi-compartment to bilayer, offering insights into polymer blend microcapsule formation and morphology.