Tuning the Morphology-Optical Property Relationship using Polymer Brush Grafted Nanorods in Polymer Nanocomposite Films

Russell Composto
University of Pennsylvania
Thursday, September 24, 2015
NCSU Golden LEAF BTEC Room 135| 4:30pm

The thermodynamic factors that affect the dispersion of polymer-brush grafted gold nanorods (NR) added to polymer matrix films have been studied by experiments and theory. When brush and matrix have a favorable interaction, nanorods uniformly disperse independent of the ratio of degree of polymerization of matrix (P) to brush (N), a = P/N. As the NR volume fraction increases, the local orientation of the NRs increases. For chemically similar brush and matrix, NRs randomly disperse for a < 2 (i.e., wet brush). For a > 2, NR’s align side-by-side in aggregates leading to a blue shift in the longitudinal surface plasmon resonance (LSPR). Self-consistent field theory (SCFT) calculations and Monte Carlo (MC) simulations indicate that NR aggregation results from depletion-attraction forces. The dry to wet brush transition is observed for NR aspect ratios from 2.5 to 7. Homogeneously grafted, chemically mixed bimolecular brushes exhibit better dispersion than unimolecular ones even when one brush is incompatible with the matrix chains. SCFT shows that the unfavorable brush collapses so that the more favorable brush forms an interface with the matrix chains. Heterogeniously grafted, mixed brushes with active linkers (alkane dithiol, peptide, DNA) on the tips of the NR are used to create chains of NRs linked end-to-end in solution and PNC films. Using polymer brushes, the optical properties of PNC films can be tuned across the visible region and into the near-IR.

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