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Author ORCID Identifier
Campus-Only Access for Five (5) Years
Doctor of Philosophy (PhD)
Polymer Science and Engineering
Year Degree Awarded
Month Degree Awarded
David A. Hoagland
Thomas P. Russell
Polymer and Organic Materials | Statistical, Nonlinear, and Soft Matter Physics
Gels and emulsions, a category of dispersed or swollen soft matter, exhibit diverse characteristics and applications. Understanding their behavior requires nanoscale visualization, making liquid-phase electron microscopy a promising approach. This thesis investigates solvated soft matter using open liquid SEM and TEM techniques, avoiding confinement by employing liquids of negligible or low volatility alongside specialized electron microscopes. We developed open liquid TEM and SEM-based high-resolution imaging methodologies for polymer gels and nanoparticle interfacial assemblies, contributing to an enhanced understanding of nanoscale features and rearrangements. A Variable Pressure Scanning Electron Microscope (VPSEM) enabled imaging of nanoparticle (NP) adsorption and dynamics on the surface of commonly used liquids such as glycerol. At low electron doses, NP motion at the liquid surface was negligibly affected by the electron beam. However, high electron doses and the use of hydrophobic liquid led to significant beam-induced artifacts. We were able to image the packing of nanorods (NRs) and nano-ellipsoids (NEs) in dense monolayers at an individual particle level on the surface of a variety of liquids with unprecedented resolution. In-situ imaging of the interfacial assembly of NRs and NEs revealed a slow reorientation behavior that depended on the NP shape, aspect ratio, polymeric ligands, and solvent. The packing of dense monolayers of rod-like NPs was influenced by the strength of interparticle interactions, which in turn depended on interparticle separation, polymeric ligands, and solvents. At high areal densities, strongly interacting NEs exhibited a morphology similar to ellipsoidal microparticles, while NEs with negligible interactions displayed local liquid crystalline order. The interfacial adsorption and packing of both NRs and NEs were significantly influenced by the grafted polymeric ligands. A TEM-based technique was used to image solvated crystalline polymers, specifically capturing PEG crystallization within thin ionic liquid films for the first time. This approach revealed novel PEG nano-crystallite morphologies that correlated with film thickness and substrate characteristics. Applying the same methodology, we characterized the gel network of PEG-IL gels, uncovering a heterogeneous network structure. Our observations revealed an interconnected gel network formed by fibrillar crystallites of PEG, spanning dimensions from a few nanometers to several hundred nanometers.
Srivastava, Satyam, "OPEN LIQUID ELECTRON MICROSCOPY: IMAGING CRYSTALLINE POLYMERS AND POLYMER-GRAFTED ANISOTROPIC NANOPARTICLES" (2023). Doctoral Dissertations. 3009.
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