Date of Award

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science

Committee Chair

Jeffrey J. Weimer

Committee Member

Isaac Torrez Diaz

Committee Member

Seyed Sadeghi

Committee Member

Vinoy Thomas

Committee Member

Bernhard Vogler

Research Advisor

Jeffrey J. Weimer

Subject(s)

Quantum dots, Thin films, Ligands, Nanoparticles, Liquid-liquid interfaces

Abstract

When nanoparticles are used as coatings on displays, solar cells, or devices, a thin, closely packed, uniform film is desired to enhance performance. Organic ligands are commonly used during the synthesis of metal or semiconductor nanoparticles. The ligands bind to the surface of the nanoparticle to control size, stability, or functionality. Commercially available nanoparticles have excess (free), ligands in their dispersions. Removal of the free ligands can potentially improve the performance of the system, especially when the dispersion is subsequently coated on a surface. Current methods to remove free ligands from nanoparticle dispersions result in mass loss, reduced performance, or decreased stability. In this study, liquid-liquid extraction is investigated as a potential method without mass loss or stripping of bound ligands. Subsequent studies determine how removing free ligands impacts the quality of Langmuir films formed from the altered dispersions. The system is CdSe/ZnS quantum dots with oleic acid ligands. Characterization is done with Fourier transform infrared spectroscopy, thermogravimetric analysis, digital imaging, Brewster angle microscopy, and white light interference spectroscopy. The results show that 94% of free ligands can be removed from quantum dot dispersions using liquid-liquid extraction without mass loss, stripping of bound ligands, or agglomeration. The method can be used for commercial applications or research to optimize the ratio of free to bound ligands and thereby reduce unnecessary expenses in ligands. The results also show that removal of free ligands changes spreading dynamics. Finally, the results show the removal of free ligands improves film quality (uniformity) across large scales. This can improve performance in devices that require a thin, closely packed, uniform film.

Comments

Submitted in ... the Joint Interdisciplinary Materials Science Program.

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