Field-directed Transport and Self-assembly of Magnetic Nanoparticles with Applications
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This dissertation includes five chapters. Chapter 1 contains a general introduction to the fundamentals of magnetism, magnetic nanoparticles and their applications. In Chapter 2, analytic solutions of magnetic fields are presented for different geometrics, including rectangular, cylindrical, and hollow cylindrical magnets. Moreover, these models are validated using a SENIS magnetic field mapper. The next chapter, Chapter 3, deals with the magnetofection. We present closed-form equations for predicting the magnetic field of an array of magnets, the magnetic force using an “effective” dipole moment approach, and a drift–diffusion equation for predicting particle transport and accumulation. The drift–diffusion equation is solved numerically for both a linear 1D and 2D axisymmetric analysis. The models have been demonstrated via application to a conventional 24-well plate magnetofection system. The analysis indicates that several factors have a significant influence on particle transport and accumulation, which in turn impact transfection efficiency, including the size of the particles, the magnet-to-well spacing, the height of the initial concentration of particles in a well and the relative orientation of magnetization in neighboring magnets, among others. In Chapter 4, we perform a theoretical study to understand the self-assembly process of the magnetic particles using two distinct and complimentary computational models, which are based on the Langevin’s equation for predicting the particle dynamics and the Monte Carlo method for the energy of the particles, respectively. Our computational models take into account several dominant assembly mechanisms, including the induced magnetostatic, magnetic dipole-dipole interactions, the electrostatic repulsion, Brownian dynamics, Van der Waals interaction and a steric repulsive force caused by surfactant-surfactant contact. One dimensional chain-like structures, 2D patterns with nanoscale resolution and 3D crystalline structures are presented in this chapter. These are useful for designing the cost effective fabrication of functional nanostructured materials for many diverse technological applications. In Chapter 5, we introduce a computational approach to optimize the optical absorption of dilute monodisperse colloids of plasmonic NPs under the constraint of a prescribed volume fraction, which is useful for the rational design of dilute colloids and process variables for a broad range of photothermal applications. Furthermore, we explored the optical properties of 1D magnetic-plasmonic chains as described in previous chapter using the finite-element (FE)-based Radio Frequency (RF) solver in the COMSOL Multiphysics program (www.comsol.com). The ability to self-assemble particles with tunable field enhancement holds potential for fundamental studies of light-matter interactions as well as applications of bio and chemical sensing.