Chen, Zhong-Ren (1998) I. Dynamics of block copolymer nanostructures. II. Polymerizability of cyclic olefins and ring-closing metathesis. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-01242008-095827
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, dynamics and thermodynamics of block copolymer nanostructures must be understood. The dynamics of flow-induced alignment of block copolymers will provide the basis to predict the direction, rate, and degree of alignment, while defect dynamics and thermodynamics will give insight into the possibilities of formation of desired nanostructures. In chapter 1, I will overview key issues of flow-induced alignment based on literature and new results from the first two chapters of the thesis. A three-dimensional mapping summarizes the flow behavior of diblock copolymers in terms of molecular characteristics and processing conditions. Various mechanisms that had been proposed since two decades ago are reviewed and re-evaluated.
In chapter 2, I will present detailed results revealed by a powerful experimental method, which combines in-situ rheo-optical measurements and ex-situ structural characterization by electron microscopy and x-ray scattering. A PS-PI (10K-10K) diblock is used as a model system. Three different trajectories of alignment are investigated: perpendicular alignment and two qualitatively different routes to parallel alignment. At the highest frequencies, 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. These explain the change in character of the pathway to parallel alignment and the emergence of perpendicular alignment with decreasing frequency. For each trajectory in general, the initial 'fast' process enhances not only the projection of the orientation distribution that corresponds to the final state, but also increases other projections of the distribution; the late-stage 'slow' process eliminates these other projections and perfects a single alignment.
ABC triblock copolymer can form a fascinating array of nanostructures. Phase behavior, dynamics of oscillatory-shear alignment, and other issues raised by ABC triblock copolymers, such as dynamics of lamellar perforation in three-nanophase-separated states will be discussed in chapter 3. Both thermotropical and shear-induced phase transitions are observed. Dramatic changes of morphology and alignment behavior are induced simply by switching the permutation of the blocks, molecular size, shear condition, and temperature. In three-nanophase-separated lamellar materials, a new type of defect is found: correlated perforation. As these defects annihilate upon annealing, long range correlations produce striking patterns, including those that resemble a ship's wake. The creation and evolution of these defect structures present challenge and opportunities in developing novel nanostructures.
Olefin metathesis by transition metal complex has been a powerful method in polymer and organic synthesis. In chapter 4, I will present a model to predict the ring-chain equilibria in ring-opening-closing reaction. Statistical mechanics and molecular mechanics provide the basic tools in problem formulation and parameter determination. Polymerizability of cyclic olefins are predicted by this model, and agree well with ring-opening metathesis polymerization 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.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Chemistry and Chemical Engineering|
|Major Option:||Chemical Engineering|
|Thesis Availability:||Restricted to Caltech community only|
|Defense Date:||9 December 1997|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||15 Feb 2008|
|Last Modified:||26 Dec 2012 02:28|
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