Theoretical and Experimental Studies on the Surface Structure of PF-b-PNIPAAm Rod-Coil Block Copolymer Brushes
Date Issued
2009
Date
2009
Author(s)
Chang, Wei-Hsuan
Abstract
A combined theoretical and experimental investigation is performed to study the surface morphology of conjugated rod-coil block copolymer brushes. Based on dissipative particle dynamics, the surface structures of thermoresponsive polymer brushes are found to alter significantly in response to the effects of thermal stimuli, grafting density, and rod-coil block ratio of the polymer brushes. Small, hemispherical domains of the aggregation of rod-blocks are formed at low temperature. As the temperature increases, the conformations transform to isolated islands, worm-like structures, or even network-like morphologies depending on the grafting density. Furthermore, the aggregations tend to submerge into coil block at first and float on the top as the temperature increases. The degree of submergence depends on rod-coil block ratio of the polymer brushes. In the experimental part, two Poly[2,7-(9,9-dihexylfluorene)]-b-poly[N-isopropylacrylamide] (PF-b-PNIPAAm) rod-coil block copolymer with different block ratios are synthesized and used to prepare corresponding polymer brushes on the quartz glass by physisorption. The morphology on the top of the surface is characterized by atomic force microscopy image. The results show a thermoresponsive transformation via temperature variation and are consistent with theoretical predictions. In addition, the surface is verified to be more hydrophobic after temperature treatment by contact angle measurements, suggesting the flotation of the rod aggregative domain on the top. The photophysical properties of PF-b-PNIPAAm polymer brushes are also found to vary by thermal stimuli. The PL spectra reveals that emission peaks originated from the aggregation and/or excimer formation of PF blocks and the intensity slightly changes through temperature variation. Our study demonstrates that the surface morphology of polymer brush and its corresponding photophysical property can be tuned by thermal stimuli.
Subjects
polyfluorene
thermoresponsive polymer
rod-coil block copolymer
polymer brush
surface structure
photophysical property
Type
thesis
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