VERTICAL EVAPORATIVE ASSEMBLY AND DOUBLE REPLICATION OF UNARY AND BINARY SILICA COLLOIDAL CRYSTAL FILMS

Open Access
- Author:
- Russell, Jennifer Lynn
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 09, 2017
- Committee Members:
- Thomas E Mallouk, Dissertation Advisor/Co-Advisor
Thomas E Mallouk, Committee Chair/Co-Chair
Benjamin James Lear, Committee Member
Lauren Dell Zarzar, Committee Member
Suzanne E Mohney, Outside Member - Keywords:
- colloidal crystal
silica
nanoparticle
template replication
self-assembly
polymer - Abstract:
- As the field of nanomaterials expands, the pursuit of smaller dimensions necessitates the ability to both synthesize nanoscale building blocks and also control their spatial arrangements. In a size regime where dimensions and structure may dictate material properties, colloidal nanoparticles are versatile nanoscale building blocks with the ability to order into diverse periodic arrangements, called colloidal crystals. There have been tremendous advancements in the area of colloidal crystal fabrication over the past few decades, but new syntheses and assembly techniques continue to develop in order to unite scale and desired material structure. In this dissertation, I describe my work from three different projects: silica binary colloidal crystal assembly, the use of colloidal crystal films in template replication synthesis, and silica nanoparticle morphological changes during assembly. In Chapter 1, I introduce colloidal crystals and review synthetic methods for silica colloid synthesis and techniques for their assembly into colloidal crystals. I also discuss template replication synthesis and provide an overview of the projects detailed in the remaining chapters. I will discuss my first project in Chapter 2, in which the phase behavior of 36 nm and 22 nm silica binary colloidal crystal films was mapped over a range of compositions and temperatures in order to optimize AB2-type binary colloidal crystal film growth. While thermodynamic phase diagrams can serve as a guide in selecting binary systems based on size ratios and what phases are energetically favorable, they do not account for the intricacies of experimental non-equilibrium conditions. Therefore, this systematic experimental approach to determining growth conditions was employed. We found that low temperature (30-35°C) film growth and a range of excess 22 nm silica produced the largest, most widespread AB2 domains in film samples. I present the phase mapping results and discuss the possible reasons for the deposition conditions-dependent phase behavior and how it might extend to future binary colloidal crystal film studies. In Chapter 3, I describe double replication of silica colloidal crystal films with the use of contracting polymers. I quantify the lattice contraction of several polymer inverse replicates of the silica colloidal crystal films through the extensive use of electron microscopy. I discuss lattice contraction as a function of colloidal template size and also polymer elastic moduli using AFM nanoindentation. It was discovered in this project that polymer inverse opal lattices re-expand upon filling with inorganic oxide sol gels. This finding negates the use of double replication for shrinking periodic structures with these contracting polymers; but the results are still interesting for double replication methodology and presented evidence of the role of surface energy in the polymer contraction/expansion process. Finally, I extended the method to double replication of binary colloidal crystal film templates of silica nanoparticles <50 nm, which produced second-generation binary colloidal crystal films in silica as well as in titania. In Chapter 4, I discuss my investigation into the shape-shifting character of L-arginine stabilized silica nanoparticles during evaporative self-assembly. First, I describe the phenomenon observed in previous experiments, which appear to be due to a combination of solution chemistry and interfacial tension factors. In order to deconvolute the many solution components possibly involved, I performed comparison analyses of purified and unpurified colloidal sols based on composition via solid-state NMR, as well as electron microscopy studies of dried sols. I systematically added reactive components to the unpurified and purified sols then evaporated them into colloidal crystal films for characterization by electron microscopy. I discuss the findings, which reveal a tendency for silica nanoparticle dissolution in L-arginine, as well as encapsulation of L-arginine and under-condensed silicate groups during silica nanoparticle synthesis. The findings suggest silica nanoparticle “softness” in solution that could ease capillary-driven deformation during drying. Additionally, results of additions of L-arginine and silicate precursor to depositing solutions are discussed and how the presence of these components contributed to morphological changes by shape-ripening during evaporative film deposition.