Synthesis and applications of anisotropic colloidal dimers

by Sijia Wang

Institution: Colorado State University
Year: 2015
Keywords: Dimers; Anisotropy; Particles; Colloids; Surface chemistry; Emulsions
Record ID: 2061241
Full text PDF: http://digitool.library.colostate.edu:80/R/?func=dbin-jump-full&object_id=462352


Nowadays, anisotropic particles have attracted a lot of attention due to their wide applications in optical display, emulsion stabilization, biomedical imaging, and active materials, and drug delivery. However, methods to produce anisotropic particles with precise tunability, large quantity, high monodispersity, and low cost are still elusive. This challenge also limits the scope of studies of those particles in both scientific research and practical applications. This thesis focuses on a special class of anisotropic particles - colloidal dimers. We have successfully developed a series of bulk synthetic strategies for dimers with geometric, interfacial, compositional, and combined anisotropies based on the modification of seeded emulsion polymerization. Dimers with geometric anisotropy show new and rich assembly structures such as Ising-like lattice and chiral clusters under AC electric fields. While dimers with interfacial anisotropy, e.g., platinum-polystyrene dimers, could be used as self-propelling motors in both AC electric fields and hydrogen peroxide solution. We discover a new type of electric-field driven propulsion mechanism based on broken symmetry in electrohydrodynamic flow. Interestingly, our dimers swim in hydrogen peroxide based on bubble propulsion, which is different from the conventional self-diffusiophoresis. With additional studies, we reveal the interconnection between these two mechanisms, which depends on the surface coating of platinum. Moreover, the geometric anisotropy of colloidal dimers are crucial to generate circular motion. We also demonstrate a new concept in making colloidal emulsifiers and phase-transfer vehicles that are important for encapsulation and sequential release of small molecules across two different phases. Finally, we explore the possibility to use non-polymerizable swelling agents such as toluene and tetraethyl orthosilicate, and investigate their impacts on making dimers with combined geometric, interfacial, or compositional anisotropies. Our method not only simplifies the procedure for synthesizing dimers, but also can be potentially extended to other types of non-polymerizable swelling agents for expanding the existing catalogue of anisotropic particles.