Dissertation/Thesis Abstract

Synthesis and Directed Assembly of Colloids with Novel Functions
by Youssef, Mena, Ph.D., New York University, 2019, 284; 22587956
Abstract (Summary)

The synthesis and assembly of nano- and micron-sized particles with novel shapes and functions is currently at the forefront of research in the materials science and the soft matter community. The synthesis of particles with new shapes provides many opportunities for the bottom-up assembly of building blocks into functional materials. However, there are many challenges for assembling particles in colloidal systems, including assembly directionality and particle reconfigurability. In this dissertation, the synthesis and directed assembly of colloidal particles with novel functions is presented. New synthetic routes are developed to prepare colloidal suspensions containing particles of uniform shape and size. In addition, particles are also engineered to have a propensity for interacting with their environments in specific ways, including responding to external stimuli and assembling in a directional manner. For the majority of these colloidal systems, a trialkoxysilane precursor is used to nucleate oil droplets via homogeneous or heterogeneous nucleation. The use of such versatile trialkoxysilane precursors provides researchers with a myriad of synthetic opportunities because of their ability to be shaped, functionalized, and hardened in bulk (on the gram scale), allowing for the mass production of particles that can change shape, act as cells for confinement, and be used as self-assembling building blocks, which are all reported in this dissertation. Physical interactions such as electrostatic, depletion, and the adsorption of polymers onto particle surfaces are employed to direct the assembly of particles in these colloidal systems. Examples of directed assembly include two- and three-dimensional crystallization, particle trapping, directional binding, and selective depletion.

In part I of this dissertation, a general introduction of colloid chemistry (chapter 1) precedes an in-depth examination of the material used throughout the majority of this dissertation (chapter 2). The material is the organosilane monomer 3-(Trimethoxysilyl)propyl methacrylate (hereafter abbreviated TPM), that can be used to make highly monodispersed liquid oil droplets that have the ability to be shaped and hardened. In chapter 2, TPM is utilized to prepare reactive oil droplets via homogeneous nucleation and is grown onto existing solid particles via heterogeneous nucleation, resulting in hybrid particles. The synthetic and instrumental methods used to prepare and characterize TPM particles are explained in chapters 1 and 2.

Part II of this dissertation describes the fabrication of functional colloids via novel synthetic routes. In chapter 3, the heterogeneous nucleation of TPM onto solid particles is exploited to obtain monodispersed hybrid particles comprised of oil droplets which contain a tunable single solid inclusion. Because TPM is reactive as a liquid, the oil is chemically or optically triggered to dewet from the solid particles, resulting in particles that can change shape upon exposure to chemical or light stimuli. This dynamic change in shape opens up a number of opportunities for the synthesis of particles with exotic shapes and self-assembly, which are both explored. In chapter 4, the hybrid particles consisting of TPM grown onto a solid template are used to synthesize colloidal Janus tubes via a templating and etching sequence. These Janus tubes have chemically distinct inner and outer surfaces. The Janus character of the tubes allows them to trap nanoparticles and exhibit directional binding onto nearby substrates. Interestingly, these Janus tubes are stable in suspension and assembly only occurs in the presence of a stimulus.

Part III of this dissertation focuses on directing colloidal assembly using the depletion interaction. In chapter 5, the depletion interaction is tuned in a number of colloidal systems containing particles with different surfaces, allowing them to assemble selectively and distinctively under a specific set of conditions. Control over the selective assembly of particles is demonstrated using bidispersed systems, where the assembly of particles is well-controlled and defined by the chemical environment that the particles are exposed to. This results in the crystallization of particles in the bidispersed suspensions into single or mixed crystals. In addition, Janus colloids are synthesized and made to selectively assemble into micellar-like structures using directional and specific depletion interactions. In chapter 6, the depletion interaction is used to probe both two- and three-dimensional assemblies of hollow silica microcubes. While the two-dimensional assemblies have been previously probed on Earth, the three-dimensional assemblies reported in this dissertation are the first among their kind. All three-dimensional crystals reported in this dissertation are formed on the International Space Station in microgravity and are imaged using confocal microscopy.

Part IV contains two appendices which contain experimental procedures and results for two side projects, namely the self-inflation of TPM into microcapsules (appendix A) and characterizing the nanoscale properties of polymers using electrophoresis (appendix B). In appendix A, the synthesis of colloidal microcapsules is reported. After obtaining monodispersed TPM oil droplets via homogeneous nucleation, as described in chapter 2, the inflation of the particles is triggered by the introduction of base, which transforms liquid TPM droplets into a double (water in oil in water) emulsion. The geometry of these capsules is tunable controllable, yielding particles with well-defined inner and outer radii and shell thicknesses. In appendix B, the functionalization of particles in colloidal systems via the installation of polymers on their surface is examined. The polymers can either be physisorbed at the particle surface or permanently grafted onto the particle surface. In either case, it is demonstrated that the presence of polymers on the surface of particles can be probed using electrophoretic light scattering to obtain information about both polymer length and density at the surface of colloidal particles. A number of different polymers and particle compositions are used to study the robustness of the analytical method.

Indexing (document details)
Advisor: Sacanna, Stefano
Commitee: Seeman, Nadrian, Kahr, Bart, Geacintov, Nicholas, Jerschow, Alexej
School: New York University
Department: Chemistry
School Location: United States -- New York
Source: DAI-B 81/5(E), Dissertation Abstracts International
Subjects: Chemistry
Keywords: Chemistry, Colloids, Functional, Materials science, Self-assembly, Synthesis
Publication Number: 22587956
ISBN: 9781392609583
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