| Self-assembly of block copolymers provide versatile means to create nanostructures with potential applications in nanotechnologies. The form and size of these structures are controlled by the type and the length of each block, and the number of blocks. Active processing using symmetry-breaking fields such as flow can extend self-assembled order into the macroscopic dimensions, thus gain desired directional properties, such as transport, optical, and electrical properties. Towards the integrated synthesis and processing of functional block copolymer nanostructures, the dynamics of flow-induced alignment of block copolymers provide the basis to predict the direction, rate, and degree of alignment, while defect dynamics and thermodynamics give insight into the possibilities of formation of desired nanostructures. Using an integrated experimental approach, which combines in-situ rheo-optical measurements and ex-situ structural characterization by electron microscopy and x-ray scattering, three different alignment trajectories are investigated: perpendicular alignment and two qualitatively different routes to parallel alignment. It is a cascade of dynamics responses of chains, nanophases, and domains during oscillatory shear that determines the alignment regimes. At the highest frequencies, chain distortion and symmetry arguments explain the transient development of a bimodal texture en route to alignment of layers parallel to the planes of shear. At lower frequencies, larger scale relaxations introduce rearrangements out of the deformation plane that permit formation of lamellae perpendicular to the shear plane. For each trajectory in general, the initial 'fast' process enhances projections of a certain range of distributions; the late-stage 'slow' process eliminates other projections and perfects a single alignment. ABC triblock copolymer can form a fascinating array of nanostructures: dramatic changes of morphology and alignment behavior are induced simply by switching the permutation of the blocks, molecular size, shear condition, and temperature. Both thermotropic and shear-induced phase transitions, and new types of defects are observed.; Olefin metathesis by transition metal complex has been a powerful method in polymer and organic synthesis. A model is developed to predict the ring-chain equilibria in ring-opening-closing reaction. Predictions on the polymerizability of cyclic olefins agree well with experiments. We have extended this model to assist ring-closing metathesis of eight-member rings, which can be a useful starting material for drug synthesis. |
