Nanostructures of crystalline block copolymers
Abstract (Summary)The phase behavior and properties of strongly segregated crystalline-amorphous diblock copolymers with rubbery amorphous block were investigated. For low crystallinity PE-containing diblock copolymers, well-ordered microphase separated morphology was observed in the melt-state. Upon crystallization, in most cases, two-dimensional crystallization confined within the microphase-separated microdomains was observed with retention of the microphase-separated morphology formed in the melt-state. However, the crystallization temperature was found to have significant effect on morphology. Both the extent of microdomain confinement on crystallization and the crystalline chain orientation inside the microdomain were observed to be crystallization temperature dependent. Utilizing the unique properties of crystalline polymers, a novel method for preparing photonic band gap crystals was developed based on self-assembly behavior of crystalline block copolymers. It opened up avenues to fabricate novel polymeric optical devices. For high crystallinity PEO containing diblock copolymers, TEM coupled with electron diffraction revealed a microphase separated, alternating lamellar morphology with PEO crystalline chains oriented perpendicular to the microdomain interface regardless of the crystallization temperature. As suggested from optical microscopy and TEM experiments, the melt microphase separated morphology acted as template for crystallization. In contrast to the extended chain crystals always preferred by homopolymers, folded chain crystals were formed for crystalline/amorphous block copolymers at equilibrium state. The results were interpreted based on thermodynamic consideration of the system. The morphology of block copolymers where both block were crystalline was also investigated in this study. The effect of soft and rigid confinement on crystallization in P(E-b -EO), a crystalline/crystalline block copolymer, was evaluated. The morphological evolution of crystalline block copolymers in thin films was studied. Multiple parallel layers of crystalline PEO were found to be in perfect orientational registry even though they were separated by approximately 10 nm thick layers of amorphous polymer.
School Location:USA - Massachusetts
Source Type:Master's Thesis
Date of Publication:01/01/2002