| Aggregate morphologies as a function of apparent pH (PH*) have been studied for PS-b-P4VP diblocks in DMF/H2O. The pH* changes are induced by addition of HCl or NaOH (100 nM to 20 mM). As the pH* increases, the morphology changes from large compound micelles to a mixture of spheres, rods, and vesicles, to spheres, to rods, back to spheres when no acid or base is added, then to rods again, back to spheres again, and finally to a mixture of spheres, rods, lamellae, and vesicles. The interplay of the charge introduction into the corona chains, shielding, and steric-solvation interaction is responsible for the complex behavior. The effect of NaCl on the neutral copolymer and the effect of pH* on a quaternized copolymer are also explored.;Thermodynamics of micellization of PS-b-PAA copolymers in DMF/water have been investigated as a function of four variables, i.e. the water content, PS block length, PAA block length, and NaCl concentration. Based on a closed association model, thermodynamic functions (DeltaG, DeltaH, and DeltaS) are estimated.;Morphological phase diagrams, as well as kinetics and mechanisms of the rod to vesicle transition for PS-b-PAA diblocks in dioxane/water have been studied. In the study of morphological phase diagrams, the regions of stability are identified for spheres, spheres and rods, rods only, rods and vesicles or rods and bilayers, vesicles or bilayers alone, and for some copolymers, more complex mixtures. Evidence is presented that spheres, rods, and vesicles represent true equilibrium structures. The influence of the water content and polymer concentration on aggregate morphologies and the effect of fractionation on the phase diagram are discussed. The block length dependence of the phase diagram is also explored. It is found that copolymers with long core-forming blocks favor the formation of vesicles, and that for copolymers with short core-forming blocks, vesicles are favored at high water contents and other bilayers at relatively low water contents. In the kinetic and mechanistic study, two consecutive first order relaxation processes are found. In the first, the rod is flattened and then converts to a lamella, while in the second, the lamella closes to form a vesicle. Two relaxation times are explored in terms of the initial water content, size of the jump in the water content, and polymer concentration. |
