Nanocrystal Assembly and Integration
By incorporating stimuli-responsive components and using thermodynamic principles, gels assembled from solvent-dispersed nanocrystals could also be dynamically reconfigured between structurally distinct states. [3]
The unique properties of nanocrystals can yield exciting functionality at larger scales. Beyond what individual nanocrystals can offer, nanocrystal assembly can exbibit emergent collective behavior, opening doors to a broader range of tunability in material properties. By understanding and carefully balancing the inter-nanocrystal attractions and repulsions, ensembles of these nanostructures can be assembled in a controlled fashion. [1, 2, 3]
Nanocrystal-in-glass composites of ITO nanocrystals in niobium oxide demonstrate superior optical and electrochemical properties, compared to either component independently, because of the interfacial bonding environment. [13] Assembly of nanocrystals into micellar coronas by block copolymer templating yields composites exhibiting order on two length scales. [7]
The Milliron group has studied nanocrystal assembly conditions across a wide range of loading configurations. Entropic depletion attractions can be tuned to form nanocrystal gels [4-6], and block copolymers or homopolymers can be used to direct the assembly of ordered structures and mesoporous networks [7, 8]. Small linker molecules can be employed to form bonds between functional ligands on the surface of neighboring nanocrystals and direct nanocrystal gel networks with structure-dependent properties. [9-12] Solution processing conditions can be manipulated to yield close-packed superlattice films with robust electronic connectivity. [13]
Small angle X-Ray scattering (SAXS) schematic diagram for nanocrystal gel assemblies reveals two length scales of structural ordering. [4]
The structure of nanocrystal assemblies can be followed by small angle X-ray scattering, which is also suitable for in situ monitoring of mesoscale transformations with external stimuli such as heat and shear. This helps guide the understanding of how underlying structural changes in assembly can impact, and tune, resulting properties.
The Milliron group also pursues research on the synergistic behaviors that result from the interfaces between nanostructures in composite materials. One such example is the increase in electrochromic response of ITO nanocrystal-in-NbOx glass composite films due to unique ordering at interfacial regions. [14, 15] This effort bridges our understanding of assembly with other research areas of the group, such as electrochromic device design and interfacial charge transport. Rational assembly design is a powerful tool to integrate the properties of nanomaterials with macro-scale functionality.
Related papers:
[1] CK Ofosu, J Kang, TM Truskett, DJ Milliron. “Effective Hard-Sphere Repulsions Between Oleate-Capped Colloidal Metal Oxide Nanocrystals,” J. Phys. Chem. Lett., 13 (2022), 11323-11329 [link]
[2] AM Green, CK Ofosu, J Kang, EV Anslyn, TM Truskett, DJ Milliron. “Assembling inorganic nanocrystal gels,” Nano Lett., 22 (2022), 1457-1466 [link]
[3] ZM Sherman, AM Green, MP Howard, EV Anslyn, TM Truskett, DJ Milliron. “Colloidal nanocrystal gels from thermodynamic principles,” Acc. Chem. Res., 52 (2021), 798-807 [link]
[4] CA Saez Cabezas, GK Ong, RB Jadrich, BA Lindquist, A Agrawal, TM Truskett, DJ Milliron. “Gelation of plasmonic metal oxide nanocrystals by polymer-induced depletion attractions,” PNAS, 115 (2018), 8925-8930 [link]
[5] CA Saez Cabezas, ZM Sherman, MP Howard, MN Dominguez, SH Cho, GK Ong, AM Green, TM Truskett, DJ Milliron. “Universal Gelation of Metal Oxide Nanocrystals via Depletion Attractions,” Nano Lett., 20 (2020), 4007-4013 [link]
[6] AM Green, S Kadulkar, ZM Sherman, TM Fitzsimons, CK Ofosu, J Yan, D Zhao, J Ilavsky, AM Rosales, BA Helms, V Ganesan, TM Truskett, DJ Milliron. “Depletion-Driven Assembly of Polymer-Coated Nanocrystals,” J. Phys. Chem. C, 126 (2022), 19507-19518 [link]
[7] R Buonsanti, TE Pick, N Krins, TJ Richardson, BA Helms, DJ Milliron. “Assembly of Ligand-Stripped Nanocrystals into Precisely Controlled Mesoporous Architectures,” Nano Lett., 12 (2012), 3872-3877 [link]
[8] GK Ong, TE Williams, A Singh, E Schaible, BA Helms, DJ Milliron. “Ordering in Polymer Micelle-Directed Assemblies of Colloidal Nanocrystals,” Nano Lett., 15 (2015), 8240-8244 [link]
[9] A Singh, BA Lindquist, GK Ong, RB Jadrich, A Singh, H Ha, CJ Ellison, TM Truskett, DJ Milliron. “Linking Semiconductor Nanocrystals into Gel Networks through All-Inorganic Bridges,” Angew. Chem. Int. Ed., 54 (2015), 14840-14844 [link]
[10] MN Dominguez, MP Howard, JM Maier, SA Valenzuela, ZM Sherman, JF Reuther, LC Reimnitz, J Kang, SH Cho, SL Gibbs, AK Menta, DL Zhuang, A van der Stok, SJ Kline, EV Anslyn, TM Truskett, DJ Milliron. “Assembly of Linked Nanocrystal Colloids by Reversible Covalent Bonds,” Chem. Mater., 32 (2020), 10235-10245 [link]
[11] J Kang, SA Valenzuela, EY Lin, MN Dominguez, ZM Sherman, TM Truskett, EV Anslyn, DJ Milliron. “Colorimetric Quantification of Linking in Thermoreversible Nanocrystal Gel Assemblies,” Sci. Adv., 8 (2022), abs7376 [link]
[12] J Kang, ZM Sherman, HSN Crory, DL Conrad, MW Berry, BJ Roman, EV Anslyn, TM Truskett, DJ Milliron. “Modular Mixing in Plasmonic Metal Oxide Nanocrystal Gels with Thermoreversible Links,” J. Chem. Phys., 158 (2023), 024903 [link]
[13] R Sharma, AM Sawvel, B Barton, A Dong, R Buonsanti, A Llordes, E Schaible, S Axnanda, Z Liu, JJ. Urban, D Nordlund, C Kisielowski, DJ Milliron. “Nanocrystal Superlattice Embedded within an Inorganic Semiconducting Matrix by in Situ Ligand Exchange: Fabrication and Morphology,” Chem. Mater., 27 (2015), 2755-2758 [link]
[14] A Llordes, G Garcia, J Gazquez, DJ Milliron. “Tunable Near-Infrared and Visible-Light Transmittance in Nanocrystal-in-Glass Composites,” Nature, 500 (2013), 323-326 [link]
[15] A Llordes, Y Wang, A Fernandez-Martinez, P Xiao, T Lee, A Poulain, O Zandi, CA Saez Cabezas, G Henkelman, DJ Milliron. “Linear Topology in Amorphous Metal Oxide Electrochromic Networks Obtained via Low-Temperature Solution Processing,” Nature Mater., 15 (2016), 1267-1273 [link]