Directed Self-Assembly of Polymer-Decorated Nanoparticles
The use of nanoparticles has grown tremendously in the past 25 years in virtually all ndustries from alternative energy formulations to drug delivery development and from semiconductor fabrication to cosmetic research. The main goal of this thesis is to shed light on the surface behavior of these universally used components. The thesis explores controlling surface reactivity of nanoparticles to great detail and concludes with a proven method to organize the nanoparticles using self-assembly. The consistent and reproducible organization of the nanoparticles has tremendous value in all industries using nanoparticles in lowering production and processing costs and time.The surface reactivity of the nanoparticles is found to be well-controlled. In Chapter 3, we show a method to control alkyne reactivity on nanoparticles using a mixture of organosilane monolayers. These surfaces have the unique ability to react with azide-terminated materials through the well-known copper catalyzed azide alkyne cycloaddition `click' reaction. We also put to use a new method to ensure that the mixed surface formed is reactively homogeneous; this novel technique will sure help research endeavors as this has not been demonstrated on surfaces of nanoparticles before. We extend our surface reactivity studies with the azide-functional surface in Chapter 4. Since we were unable to create a homogeneous surface using the methods described in Chapter 3, we looked to creating a mixed monolayer by kinetic control. This involved fabrication of a bromine-terminated surface and subsequent incomplete substitution of the bromide to azide. This method of creating mixed monolayers was shown to be universally applicable to surfaces of different chemical nature and different surface geometries with the same reaction kinetics. We also contend that this method of creating mixed monolayers is novel and it provides for an additional in the control of other surface reactivity groups. Chapter 5 provides the grand finale of the thesis with the intended use of the mixed monolayers surfaces to organize nanoparticles. We show that by carefully controlling the amount of polymer chemisorbed onto a surface, the self-assembly behavior of the particles is changed. In such a method we constructed a phase diagram showing how polymeric coverage controls selfassembly. We also ensured that the phases formed were indeed equilibrated structures by studying the formation of the phases under different preparation conditions. We encountered sheets, rods, and agglomerates and were able to consistently create these structures as well as study them using image analysis.
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