| Intensive research on block copolymers for their unique phase behavior and natural application as surfactants has gone on for a number of years now. The introduction of these materials into selective solvents has expanded the range of their application to diverse areas, from biological scaffolds and drug delivery to ceramics processing and nanocomposites. This dissertation focuses on a system of AB diblock copolymers and ABA triblock copolymers in the same B selective solvent. In fact, the solvent is only selective for the B blocks at low temperatures. At high temperatures both blocks are readily soluble and the polymers are quite mobile in solution, though upon cooling the copolymers form spherical micelles with the A blocks in the micelle core and B blocks in the micelle corona. The main difference between the diblock and triblock copolymer solutions is that in the triblock copolymer solutions the B midblocks have the ability to form bridges between micelles, ultimately forming a connected network of micelles. The formation of this connected network or gel occurs very quickly over a narrow temperature range and is reversible. It transforms the solution at elevated temperatures from a concentrated polymer solution that exhibits very little elasticity to a soft gel which is mostly elastic in its mechanical response. The fast transition, low elasticity at elevated temperatures, and surfactant nature of the block copolymers all make this a model system for the study of carbon nanotubes as fillers in polymers. Carbon nanotubes have been shown to exhibit unique mechanical, electrical, thermal, and optical properties which make them a potentially interesting filler material in polymer composites. The mechanical properties of both these nanocomposites and the nascent copolymer solutions have been studied extensively in this text. This research was motivated by a desire to understand structural development on a fundamental level for both the networks of block copolymers and carbon nanotube fillers. A number of experimental techniques and theoretical methods have been used to identify and characterize the network formation in these systems. |
