Date of Award

8-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

School of Materials Science and Engineering

Committee Member

Dr. Olga Kuksenok, Committee Chair

Committee Member

Dr. Konstantin G. Kornev

Committee Member

Dr. Igor Luzinov

Abstract

Designing soft, active materials that change their shape and properties depending on external stimuli is a rapidly developing area of research. Using theoretical and computational modeling, we focus on the dynamics of gel filled with uniformly distributed ferromagnetic nanoparticles exposed to electromagnetic (EM) waves in the GHz frequency range. For the polymer matrix, we choose Poly(N-isopropylacrylamide) (PNIPAAm) gels, which have a lower critical solution temperature and shrinks upon heating. When these composites are irradiated with EM waves that have frequency close to that of the Ferro-Magnetic Resonance (FMR) frequency, the heating rate increases dramatically. The magnetically induced heating inside the nanoparticles is transferred to the gel matrix. We show that the dissipated EM energy causes volume phase transitions in the gel, as a response to temperature change, leading to the large deformations of the sample for a range of system parameters. We propose a model that accounts for the dynamic coupling between the elastodynamics of polymer gels and FMR heating of magnetic nanoparticles. This coupling is non-linear: as the system is heated and the gel shrinks at the temperatures close to the volume phase transition temperature, the particles concentration increases, which in turn results in an increase of the heating rates as long as the concentration of nanoparticles does not exceed a critical value. We show that the system exhibits high selectivity to the frequency of the incident EM radiation and can result in a large mechanical feedback in response to the time-varying power signal. These results suggest a design of a new class of soft active gel-based materials remotely controlled by the low power EM signals within the GHz frequency range.

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