Hybrids

We study the incorporation of nanoparticles or small molecules into block copolymers to facilitate self-assembly. The structural and chemical characteristics of these additives can increase segregation strength, and in some cases dictate morphology.  Simultaneous increases in additive loading and segregation strength provide unique opportunities to design and realize well-ordered, highly filled composite materials. The additives can also convey structural control. For example, the chirality of tartaric acid induces helical domains into PtBA-b-PEO block copolymers as shown below.  These approaches enable us to precisely control the composition, morphology, and spatial orientation of hybrid materials at nanometer length scales over macroscopic volumes for use in optical, electronic and magnetic materials.

3.jpg

Figure. Helical superstructures were induced in poly(ethylene oxide)-b-poly(tert-butyl acrylate) (PEO-b-PtBA) achiral diblock copolymers (BCPs) through the simple addition of pure enantiomers of tartaric acid

Block copolymer-nanoparticle hybrid materials

The composition and spatial organization of periodic hybrid materials determine their properties, performance, and utility. Block copolymers have long been cited as potential templates for ordered periodic materials, however the addition of nanoparticles and other functional additives are often constrained by loss of order, even at modest additive loadings.  The incorporation and organization of particles depends on a balance of entropic penalties due to polymer chain stretching to accommodate the nanoparticles and enthalpic contributions arising from the interactions of nanoparticle ligand with the host domain. These difficulties can be overcome by introducing strong specific interactions, such as hydrogen bonds, between the nanoparticles and at least one segment of the block copolymer.  Using this approach we can achieve nanoparticle loadings in excess of 70 wt.% in the target domains and nanoparticle sizes that approach the domain width. Such structures are of interest for many applications. To learn more, click here. 

4.jpg

Figure. Illustration of Gold NP Self-Assembly in PS-bPEO Brush BCPs through Hydrogen-Bonding Interactions between Phenol Groups on the Gold Surface and PEO Side Chains of the BCP; A Cylindrical Morphology Is Formed as a Result of an NP-Induced Asymmetry of the Side-Chain Lengths of a Symmetric Brush BCP

We use these concepts to  fabricate well-ordered 1D photonic crystals and metallodielectric metamaterials by incorporating ultrahigh loading of ZrO₂ and gold nanoparticles, respectively, into bottle brush-block copolymers (BBCPs).  The BBCPs provide access to large domain sizes that can interact with visible light and near-IR light and rapid self-assembly that is consistent with practical manufacturing schemes.

5.jpg

Figure. A robust strategy for the rapid and scalable fabrication of well‐ordered metallodielectric 1D photonic crystals through the self‐assembly of brush block copolymers and gold nanoparticles is demonstrated. The optical properties of the photonic crystals containing ultrahigh loadings of the gold nanoparticles are thermally tunable through the creation of a network structure of the nanoparticles.

Magneto-dielectric and magneto-optic metamaterials

Magnetic nanoparticles play a major role in recording media, biomedical imaging, antennas and optical materials including magneto dielectric-metamaterials.  We collaborated with Prof. Robert Norwood (University of Arizona) to fabricate magneto-optical materials with excellent Faraday rotation response.  We incorporated gallic acid functionalized FePt nanoparticles with different core diameters in to a linear diblock copolymer.  The diblock copolymer acted as a template to selectively assemble the FePt nanoparticles within one of the domain, which resulted in excellent magneto-optical performance.

6.jpg

Figure. Surface modification of FePt NPs using gallic acid (GA) as a hydrogen bonding donor followed by selective NP dispersion in the P2VP domain within a symmetric PS-bP2VP BCP template.

Related publications:

• Miles, A.; Gai, Y.; Gangopadhyay, P.; Wang, X.; Norwood, R. A.; Watkins, J. J., 2017 "Improving Faraday rotation performance with block copolymer and FePt nanoparticle magneto-optical composite". Opt. Mater. Express, 7 (6), 2126-2140. 
• Song, D.-P.; Li, C.; Li, W.; Watkins, J. J., 2016 “Block Copolymer Nanocomposites with High Refractive Index Contrast for One-Step Photonics.” ACS Nano, 10, 1216-1223. 
• Song, D.-P.; Gai, Y.; Yavitt, B. M.; Ribbe, A.; Gido, S.; Watkins, J. J.; 2016 “Structural Diversity and Phase Behavior of Brush Block Copolymer Nanocomposites.” Macromolecules , 49(17), 6480-6488. 
• Song, D.P., Lin, Y., Gai, Y., Colella, N.S., Li, C., Liu, X.H., Gido, S. and Watkins, J.J., 2015. Controlled supramolecular self-assembly of large nanoparticles in amphiphilic brush block copolymers. Journal of the American Chemical Society, 137(11), pp.3771-3774.
• Song, D.P., Li, C., Colella, N.S., Xie, W., Li, S., Lu, X., Gido, S., Lee, J.H. and Watkins, J.J., 2015. Large-volume self-organization of polymer/nanoparticle hybrids with millimeter-scale grain sizes using brush block copolymers. Journal of the American Chemical Society, 137(39), pp.12510-12513.
• Yao, L., Lu, X., Chen, S. and Watkins, J.J., 2014. Formation of helical phases in achiral block copolymers by simple addition of small chiral additives. Macromolecules, 47(19), pp.6547-6553.
• Lin, Ying; Daga, Vikram K.; Anderson, Eric R.; Gido, Samuel P.; Watkins, James J., 2011 "Nanoparticle-Driven Assembly of Block Copolymers: A Simple Route to Ordered Hybrid Materials." Journal of the American Chemical Society, 133 (17), 6513-6516.