| Dilute solution experiments employing steady state fluorescence spectroscopy were conducted to investigate the phenomenon of chain exchange between micelles. PS-PEO diblocks synthesized with fluorescent labels at the junction point were used in aqueous solution. Results showed that on mixing two different micellar solutions, the micelles equilibrated by exchanging chains with one another. This process was found to be restricted by lower and upper limits for both temperature and concentration. Within the window provided by the concentration and temperature limits, a rate constant for the chain transfer process was measured by empirical fit to experimental data. A mechanism for the process was also devised and rate equations were derived based on this mechanism.;The systems were characterized by means of visual inspection and calculations of chain dimensions, orientation correlations, total energies, pair correlations and structure factors. The order-disorder transition was followed and the results from various properties were compared for both cases of non-selective and selective solvents. From the results of the studies on systems with selective solvent, a phase diagram for diblock copolymers in solution as a function of polymer concentration and a phase diagram for diblock copolymers as a function of compositional asymmetry were calculated.;Monte Carlo simulations were performed by modeling symmetric diblock chains as self-avoiding random walks on a cubic lattice with periodic boundary conditions. Concentration of the polymer was varied to cover a wide range. In the first case, where lattice sites not occupied by a polymer bead were treated as voids or non-selective solvent, the copolymer underwent an order-disorder transition to form alternating lamellae of the two blocks. The lamellae formation took place only when the polymer formed the major component of the system and the transition point weakly depended on the concentration. In the second case where the empty lattice sites were treated as selective solvent, the insoluble blocks were seen to aggregate into various morphologies. Spherical, cylindrical, helical, OBDD and lamellar morphologies were observed as a function of concentration, in that order. These results were compared to the morphologies accessible to an asymmetric diblock melt. This study is the first known observation of helical morphology in diblock copolymer systems. |
