"Directed assembly of magnetic binary suspensions" by David H. Harris

Date of Award

2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science

Committee Chair

Isaac Torres-Díaz

Committee Member

Yuping Bao

Committee Member

Maria Pour

Committee Member

Judy Schneider

Committee Member

Carmen Scholz

Research Advisor

Isaac Torres-Díaz

Subject(s)

Colloids, Anisotropy, Magnetism, Ellipsoid-dipole model

Abstract

Colloids are particle suspensions in a continuous medium. The particle interactions promote the assembly of structures under the influence of a magnetic field, known as directed-assembly. The magnetic properties and shape anisotropy are relevant features of the particle building blocks to the assembled structures. The dipolar interaction between colloidal particles for directed assembly has been extensively modeled considering spherical particle potentials, which is inaccurate when anisotropic particles are at close range. This research aims to address the problem of quantifying the dipolar interaction between arbitrarily positioned and oriented ellipsoids with different aspect ratios and material properties. We combine the recently developed ellipsoid-dipole model and the orientation parametrization of the orientational space with the unit quaternions to quantify the dipolar interaction energy between arbitrarily positioned and oriented ellipsoids. We implement the dipolar interaction energy using the ellipsoid-dipole model in a Monte Carlo algorithm to simulate the assembly of binary suspensions of paramagnetic spheres and diamagnetic ellipsoids in a two-dimensional confinement. We analyze the assembled structures using pair correlation functions and order parameters of the mixture and the independent components. Our results show that local order and symmetry of the assembled structures are tunable under the influence of a uniform magnetic field when one component of the structure is dilute with respect to the other. We also show tunable assembled structures by changing the medium permeability and relative concentration between particle components. The simulations predict a variety of assembled structures, such as triangular structures of ellipsoids enclosing a sphere, chains of ellipsoids linked by spheres, and isotropic systems. These results indicate potential in customizing the assembled structures by tuning both medium and particle properties in binary colloidal suspensions.

Comments

Submitted ... in the joint interdisciplinary Materials Science program.

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