Surface chemistry mediated assembly of polymer-grafted nanorods in solution and polymer matrices.

摘要

In the dissertation, I investigate ways to assemble nanorods, typically made of gold, in solution and polymer matrices by controlling surface chemistry. Gold nanorods were anisotropically functionalized with polymer on the side and alkane dithiol on the end causing the gold nanorods to spontaneously assemble in solution. The assembly could be tuned by controlling the incubation time which affected the solution absorbance due to plasmon coupling. Linked gold nanorods were cast in polymer thin films and their optical properties were imparted to the film. This anisotropic functionalization method was utilized to placed DNA or peptides on the ends of the gold nanorods allowing for reversibly assembly. In the case of DNA, assembly was reversed upon heating and could be tuned by controlling the concentration of the complimentary DNA strand. In the case of the peptide, assembly was triggered by the presence of Zn 2+ ions and could be reversed by adding in a chelater. Anisotropic modification of the nanorods could also be used to assemble organic semiconductors around the nanorods at specific facets. Here, organic semiconductors rhodamine-B, 5(6)-carboxyfluorescein, and cyanine-3 were assembled onto the surface of gold nanorods. By tuning the surface chemistry the organic semiconductors would assemble around the nanorods in different ways which resulted in unique optical properties. The dispersion of PMMA-grafted mesoscopic iron-oxide rods in polymer matrices was studied by varying the PMMA brush molecular weight (N) polymer matrix molecular weight (P), and polymer matrix type. Here, we found that the ratio of P/N and matrix type had little effect on dispersion of iron-oxide mesorods. N was found to be the main factor that determined dispersion, which is attributed to the large size of the mesorods. Long PS and short PMMA brushes were grafted to gold nanorod surfaces and the dispersion of this system in PS and PMMA was investigated by controlling matrix molecular weight. We found that the gold nanorods would disperse in PS matrices 24 times larger than the grafted brush, while in PMMA matrices the nanorods would aggregate. SCFT calculations revealed that the good dispersion is most likely due to the collapse of the short PMMA brush and the enthalpic penalty for the collapse of the PS brush onto the PMMA brush. Finally, PS-grafted gold nanorods were assembled in liquid crystals. Assembly was tuned by controlling temperature and liquid crystal defect structure in the presence of micropillar arrays. The assembly of the nanorods resulted in changes in characteristic absorbance peaks of over 100 nm. From these studies, we are able to predict and control the assembly of nanorods in both solution and polymer matrices allowing us to fine-tune optical properties.