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Document Type

Campus-Only Access for One (1) Year

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2017

Month Degree Awarded

May

First Advisor

James J. Watkins

Subject Categories

Polymer and Organic Materials

Abstract

The “bottom-up” fabrication of functional hybrid material can be achieved by using directed self-assembly of functional nanoparticles (NP) and block copolymers (BCP) as templates. The versatile nanostructures of BCP provide possibilities to precisely control NPs spatial distribution and the resulting hybrid materials exhibit enhanced electrical, mechanical and optical functionalities. Three main topics related to BCP/NP composites are discussed in this dissertation: I) the spatial distribution of large NP in linear BCP; II) the morphology control of BCP templates with new architectures; and III) the magneto-optical properties of hybrid material using magnetic NPs.

For well-ordered BCP/NP composite, the ratio of NP core diameter (dcore) and BCP domain width (L) has been generally limited with dcore/L < 0.3 when BCP/NP interactions are relatively neutral or weak. By modifying the Au NPs with hydrogen bonding (H-bonding) donor group, the selective spatial distribution of Au NPs ranges in size up to 0.8 times that of the target domain width in symmetric polystyrene-block-poly (2-vinylpyridine) (PS-b-P2VP). In addition, H-bonding meditated 15 nm NPs can be directed by linear BCP of dcore/L up to 0.4 at 20wt % loading. The H-bonding interactions between NP and BCP provide favorable enthalpic interaction to overcome the inherent entropy penalties mainly arising from polymer chain stretching upon the sequestration of large particles.

On the other hand, the extensive chain entanglements of linear BCP still remain a challenge for hybrid materials with the consequence of long processing duration, many defects and lack of orientation. Bottlebrush BCPs (BBCPs) exhibit much lower degree of chain entanglement due to the highly extended confirmation. A systematic study was conducted to investigate the morphology transitions that occur in polystyrene-block-poly (ethylene oxide) (PS-b-PEO) BBCPs upon varying PEO volume fraction (fPEO) from 22 % to 81 %. Either symmetric or asymmetric lamellar morphologies were observed in the BBCPs over an exceptionally wide range of fPEO from 28 % to 72 %. A microphase transition temperature TMST was observed over a temperature range of 150-180 ℃.

Finally, enhanced magneto-optical (MO) composites with excellent Faraday rotation (FR) response were fabricated using iron platinum (FePt) NPs and PS-b-P2VP linear BCP. Gallic acid (GA) functionalized FePt NPs with average dcore from 1.9 to 9.3 nm were selectively incorporated into a P2VP domain through H-bonding interactions. The use of copolymer template to selectively arrange the magnetic NPs enabled high MO performance with limited trade-off of scattering loss, providing a simple strategy to prepare functional materials for MO applications. Verdet constants of a 10 wt % loaded 4.9 nm FePt NP composite reached absolute magnitudes as high as ~ -6×104 °/T⋅m at 845 nm, as determined by FR measurements at room temperature, which is comparable to today’s benchmark materials.

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