Tuning the Structures of Magnetic Nanoparticles and Thermoresponsive Polymers Towards Magneto-Thermoresponsive Particles
Date of Award
Doctor of Philosophy (PhD)
School of Materials Science and Engineering
Metal substituted ferrite nanoparticles (MxFe3-xO4, M = Mn, Co, Ni, or Zn) have been synthesized and applied for a variety of biomedical applications, including magnetic hyperthermia treatment, drug delivery, and tunable MRI contrast agents. To better understand the structure-property relationship of such materials, nonstoichiometric manganese ferrite was computationally modeled with density functional theory (DFT). Detailed XRD and HRTEM analysis suggest that substitution-induced crystalline defects cause a discrepancy between the computational results and the experimental results. To improve the control of the size, and composition of the ferrite nanoparticles, a seed-mediated drip synthesis method and post-synthesis oxidation method were developed. Manganese-cobalt substituted ferrite nanoparticles were synthesized and characterized. The results showed an insufficiently oxidized core-oxidized shell structure leading to a shell-dominated magnetic property. To solve the insufficient oxidation issue and to better control the crystalline structure of the ferrite nanoparticles, a post-synthesis annealing method was developed. The results indicated that the wüstite rich nanoparticles can be oxidized by post-synthesis annealing without the addition of oxidizing agents. For 20 nm iron oxide nanoparticles, the saturation magnetization increased from 35 Am2/kg to 72 Am2/kg and exhibited a specific absorption rate of 240 W/g under a 212 kHz, 33 mT AC field. To study the structure-property relationship of the 4-arm polypropylene oxide (PPO)–polyethylene oxide (PEO) block copolymers, a series of polymer hydrogels with various molecular weights, block molar ratios, and solution concentrations were prepared via anionic ring-opening polymerization. The chemical structures were determined by nuclear magnetic resonance (NMR) and the thermal properties were tested by differential scanning calorimetry (DSC). The resulting data were statistically analyzed, and a corresponding empirical model was developed. The empirical model indicated the thermoresponsive temperature is positively correlated with the EO/PO ratio and negatively correlated with the molecular weight and concentration. The empirical model was then challenged through the synthesis of 3 targeted polymers and resulted in an RDS of less than 5%. Particles with high heating efficiency were surface modified with thermoresponsive PEO-b-PPO ligands via ligand exchange and silica surface chemistry. The polymer-particle complex showed magneto-thermoresponsiveness that is potentially used in magnetically triggered drug release in the future.
Yan, Zichun, "Tuning the Structures of Magnetic Nanoparticles and Thermoresponsive Polymers Towards Magneto-Thermoresponsive Particles" (2021). All Dissertations. 2879.