Seminario del Máster en Física: Radiaciones, Nanotecnología, Partículas y Astrofísica de la Universidad de Granada, impartido por James E. Martin (Sandia National Labs, Albuquerque, New Mexico (EE.UU.).
Resumen: Triaxial magnetic fields, comprised of three orthogonal field components, at least two of which are alternating, are a relatively new area of scientific investigation. When such fields are applied to magnetic particle suspensions, a wide variety of phenomena emerge, including vigorous fluid vorticity, complex flow patterns, and biomimetic dynamics. When magnetic particles are instead suspended in a polymer resin, triaxial fields can be used to create complex particle organizations that greatly enhance the physical properties of the composite.This research will be covered in two lectures, the first covering how triaxial fields can be used to induce fluid vorticity, flow lattices and biomimetic dynamics. The underlying cause of fluid vorticity will be shown to be due to aspects of the symmetry of the union of the Lissajous trajectories of the field and its converse. The symmetry theory can predict the direction of the vorticity vector as a function of the field frequencies and predict phase changes required to reverse the flow. A theory of the dynamics of the volatile particle chains that form under triaxial fields is also described, as well as the concept of a field symmetry transition. It will be also shown that this can be used to create an infinite variety of fluid flows having vorticity vectors that orbit in three-dimensional space. Such flows are maximally efficient in mixing in complex volumes and can be used to create striking biomimetic dynamics, such as bees, swimming serpents, ameboid pseudopodia motions, and the streaming strand motion of slime molds. Finally, it will be shown that when such fields are applied to suspensions of magnetic platelets, highly organized flow lattices emerge.The second lecture will describe the formation of magnetic particle composites in triaxial fields. Balanced triaxial fields – those for which all three field components have equal rms amplitudes – create time-average (ponderomotive) interactions that cancel to first order, wherein the particle dipole moments are assumed to be induced by the applied field alone. However, in the self-consistent local field approximation, where the field that polarizes the particles includes contributions from the dipole fields of other particles, a strong, many-body interaction arises. At low particle loadings clusters with molecular-like geometries emerge. At higher particle loadings a wide variety of composite structures can be produced, both isometric and anisometric. The physical properties of these composites are significantly enhanced by triaxial field structuring. Examples of composite structures, both simulated and real, will be shown, and a theory of physical properties such as the magnetic susceptibility and thermal conductivity will be described and compared to experiment. Applications include chemical sensors, strain sensors and tin whisker mitigation films.
- Fecha: 30 y 31 de mayo de 2022
- Lugar: Aula A03 (aulario) de la Facultad de Ciencias
- Horario: de 12:00 a 13:00 horas
- Organiza: Máster en Física: Radiaciones, Nanotecnología, Partículas y Astrofísica de la Universidad de Granada
- Más información:
Fernando Vereda
Associate Professor
Magnetic Soft Matter Group
Singular Laboratory in Advanced Technologies F2N2Lab
Department of Applied Physics
fvereda@ugr.es