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Colloid assembly and actuation under magnetic and electric fields
Gao, Yan
Gao, Yan
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2025
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Active colloidal particles, typically ranging from 10 nms to 10 µms in size, have attracted significant attention over the past few decades for their ability to be controlled by external fields. In this thesis, we investigate the assembly of colloidal particles into three systems of increasing complexity, the first two manipulated with applied magnetic fields and the third with combined magnetic and electric fields.
We begin by demonstrating that a single applied magnetic field can be used to assemble simple spheres into uniform colloidal chains. These chains can be varied from two to four to eight monomers in length and serve as the building blocks for more complex superstructures.
For our second study, we demonstrate that simple colloidal spheres can be assembled into microbots using an applied magnetic field. We determine, however, that these active devices are rigid and face challenges such as limited biocompatibility, inefficient drug loading, and surface slip. To address these issues, we introduce magnetically controlled soft microbots based on emulsion droplets decorated with simple magnetic colloidal spheres at their outer surface. Soft microbots can roll like deflated tires under magnetic fields, which change the lubrication layer and increase the contact area of soft robots. This inherent deformability can enhance traction significantly, supported by numerical simulations and theoretical analysis.
Finally, we extend control over motion and functionality using a hybrid actuation strategy like combined electric and magnetic fields. This method enables fine-tuning of interparticle interactions, leading to more complex and novel structures. One such structure is the dodecagonal quasicrystal, which displays “forbidden” symmetries and long-range orientational order without periodicity, first discovered in synthetic alloys and later in Nature. When the quasicrystal building blocks are colloidal particles, the formation processes slow dramatically, allowing for real-time, in-situ observation and providing a valuable platform for studying the dynamics.
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