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Dissertation
The Formation of One-Dimensional and Two-Dimensional Poly(L-Lactic Acid) Crystals via Evaporative Crystallization on Water Surface
Doctor of Philosophy (Ph.D.), Drexel University
Sep 2023
DOI:
https://doi.org/10.17918/00001885
Abstract
Solvent evaporation is one of the most fundamental processes in soft matter. Structures formed via solvent evaporation are often complex yet tunable via the competition between solute diffusion and solvent evaporation time scales. Controlling the evaporation process has profound effects on the coating, printing, food, membrane, and pharmaceutical industries. This dissertation concerns the polymer evaporative crystallization on water surface (ECWS). The dynamic and two-dimensional nature of the water surface offers a unique way to control the crystallization pathway of polymeric materials. Using poly(L-lactic acid) (PLLA), we demonstrate that both one-dimensional (1D) crystalline filaments and two-dimensional (2D) lamellae are formed via ECWS, in stark contrast to the 2D Langmuir-Blodget monolayer systems as well as polymer solution crystallization. Results show that this biphasic 1D/2D structure is tunable via chemical structures such as molecular weight and polarity of the polymer and processing conditions such as temperature, evaporation speed, and interfacial tension. We show that the 1D crystals are formed by interfacial crystallization of pinned PLLA chains at the liquid/liquid interface, while 2D lamellae are formed where less confinement on the chain conformation is imposed. Only 1D filaments are formed when poly(L-lactic acid)-b-poly(ethylene oxide) (PLLA-b-PEO) block copolymer is employed in ECWS, which is attributed to the strong pinning effect of the block copolymer imparted by the hydrophilic PEO block. The formation of 1D crystals follows a nucleation-merging process, different from the classical nucleation and growth mechanism. The nucleation-merging process mimics the recently discovered particle-mediated crystallization in biominerals and the so-called nodule structures in polymer bulk. This intriguing observation reveals the feasibility of altering the polymer's crystallization pathways by changing the energy landscape of the intermediate states. This dissertation work demonstrates that ECWS provides a rich platform to tune polymer crystallization pathways. It also offers a unique approach to fabricating nanomaterials and polymer thin films with tunable morphology.
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Details
- Title
- The Formation of One-Dimensional and Two-Dimensional Poly(L-Lactic Acid) Crystals via Evaporative Crystallization on Water Surface
- Creators
- Qian Qian
- Contributors
- Christopher Y. Li (Advisor)Andrew J. D. Magenau (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xvi, 125 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Materials Science and Engineering; College of Engineering; Drexel University
- Other Identifier
- 991021230106604721