Improving nanoparticle superlattice stability with deformable polymer gels.

The self-assembly of colloidal nanoparticles into ordered superlattices typically uses dynamic interactions to govern particle crystallization, as these non-permanent bonds prevent the formation of kinetically trapped, disordered aggregates. However, while the use of reversible bonding is critical in the formation of highly ordered particle arrangements, dynamic interactions also inherently make the structures more prone to disassembly or disruption when subjected to different environmental stimuli. Thus, there is typically a trade-off between the ability to initially form an ordered colloidal material and the ability of that material to retain its order under different conditions.

Nanocomposite tectons as unifying systems for nanoparticle assembly.

Nanocomposite tectons (NCTs) are nanocomposite building blocks consisting of nanoparticle cores functionalized with a polymer brush, where each polymer chain terminates in a supramolecular recognition group capable of driving particle assembly. Like other ligand-driven nanoparticle assembly schemes (for example those using DNA-hybridization or solvent evaporation), NCTs are able to make colloidal crystal structures with precise particle organization in three dimensions. However, despite the similarity of NCT assembly to other methods of engineering ordered particle arrays, the crystallographic symmetries of assembled NCTs are significantly different.

Macroscopic materials assembled from nanoparticle superlattices.

Nanoparticle assembly has been proposed as an ideal means to program the hierarchical organization of a material by using a selection of nanoscale components to build the entire material from the bottom up. Multiscale structural control is highly desirable because chemical composition, nanoscale ordering, microstructure and macroscopic form all affect physical properties. However, the chemical interactions that typically dictate nanoparticle ordering do not inherently provide any means to manipulate structure at larger length scales.

Reinforcing Supramolecular Bonding with Magnetic Dipole Interactions to Assemble Dynamic Nanoparticle Superlattices.

Assembling superparamagnetic particles into ordered lattices is an attractive means of generating new magnetically responsive materials, and is commonly achieved by tailoring interparticle interactions as a function of the ligand coating. However, the inherent linkage between the collective magnetic behavior of particle arrays and the assembly processes used to generate them complicates efforts to understand and control material synthesis. Here, we use a synergistic combination of a chemical force (hydrogen bonding) and magnetic dipole coupling to assemble polymer-brush coated superparamagnetic iron oxide nanoparticles, where the relative strengths of these interactions can be tuned to reinforce one another and stabilize the resulting superlattice phases.

Dictating Nanoparticle Assembly via Systems-Level Control of Molecular Multivalency.

Nanoparticle assembly can be controlled by multivalent binding interactions between surface ligands, indicating that more precise control over these interactions is important to design complex nanoscale architectures. It has been well-established in natural materials that the arrangement of different molecular species in three dimensions can affect the ability of individual supramolecular units to coordinate their binding, thereby regulating the strength and specificity of their collective molecular interactions. However, in artificial systems, limited examples exist that quantitatively demonstrate how changes in nanoscale geometry can be used to rationally modulate the thermodynamics of individual molecular binding interactions.

Multistimuli Responsive Nanocomposite Tectons for Pathway Dependent Self-Assembly and Acceleration of Covalent Bond Formation.

Nanocomposite tectons (NCTs) are a recently developed building block for polymer-nanoparticle composite synthesis, consisting of nanoparticle cores functionalized with dense monolayers of polymer chains that terminate in supramolecular recognition groups capable of linking NCTs into hierarchical structures. In principle, the use of molecular binding to guide particle assembly allows NCTs to be highly modular in design, with independent control over the composition of the particle core and polymer brush. However, a major challenge to realize an array of compositionally and structurally varied NCT-based materials is the development of different supramolecular bonding interactions to control NCT assembly, as well as an understanding of how the organization of multiple supramolecular groups around a nanoparticle scaffold affects their collective binding interactions.

Assembling Ordered Crystals with Disperse Building Blocks.

Conventional colloidal crystallization techniques typically require low dispersity building blocks in order to make ordered particle arrays, resulting in a practical challenge for studying or scaling these materials. Nanoparticles covered in a polymer brush therefore may be predicted to be challenging building blocks in the formation of high-quality particle superlattices, as both the nanoparticle core and polymer brush are independent sources of dispersity in the system. However, when supramolecular bonding between complementary functional groups at the ends of the polymer chains are used to drive particle assembly, these "nanocomposite tectons" can make high quality superlattices with polymer dispersities as large as 1.

Self-Assembling Nanocomposite Tectons.

The physical characteristics of composite materials are dictated by both the chemical composition and spatial configuration of each constituent phase. A major challenge in nanoparticle-based composites is developing methods to precisely dictate particle positions at the nanometer length scale, as this would allow complete control over nanocomposite structure-property relationships. In this work, we present a new class of building blocks called nanocomposite tectons (NCTs), which consist of inorganic nanoparticles grafted with a dense layer of polymer chains that terminate in molecular recognition units capable of programmed supramolecular bonding.