Investigating Polymer Transformation during the Encapsulation of Metal Nanoparticles by Polystyrene-b-poly(acrylic acid) in Colloids

Synthesis of Patchy Nanoparticles with Symmetry Resembling Polar Small Molecules

Patchy nanoparticles (NPs) show many important applications, especially for constructing structurally complex colloidal materials, but existing synthetic strategies generate patchy NPs with limited types of symmetry. This article describes a versatile copolymer ligand-based strategy for the scalable synthesis of uniform Au-(SiO₂ )_x patchy NPs (x is the patch number and 1 ≤ x ≤ 5) with unusual symmetry at high yield. The hydrolysis and condensation of tetraethyl orthosilicate on block-random copolymer ligands induces the segregation of copolymers on gold NPs (AuNPs) and hence governs the structure and distribution of silica patches formed on the AuNPs. The resulting patchy NPs possess unique configurations where the silica patches are symmetrically arranged at one side of the core NP, resembling the geometry of polar small molecules. The number, size, and morphology of silica patches, as well as the spacing between the patches and the AuNP can be precisely tuned by tailoring copolymer architectures, grafting density of copolymers, and the size of AuNPs. Furthermore, it is demonstrated that the Au-(SiO₂ )_x patchy NPs can assemble into more complex superstructures through directional interaction between the exposed Au surfaces. This work offers new opportunities of designing next-generation complex patchy NPs for applications in such as biomedicines, self-assembly, and catalysis.

Polymer-Tethered Nanoparticles: From Surface Engineering to Directional Self-Assembly

ConspectusCurrent interest in nanoparticle ensembles is motivated by their collective synergetic properties that are distinct from or better than those of individual nanoparticles and their bulk counterparts. These new advanced optical, electronic, magnetic, and catalytic properties can find applications in advanced nanomaterials and functional devices, if control is achieved over nanoparticle organization. Self-assembly offers a cost-efficient approach to produce ensembles of nanoparticles with well-defined and predictable structures. Nanoparticles functionalized with polymer molecules are promising building blocks for self-assembled nanostructures, due to the comparable dimensions of macromolecules and nanoparticles, the ability to synthesize polymers with various compositions, degrees of polymerization, and structures, and the ability of polymers to self-assemble in their own right. Moreover, polymer ligands can endow additional functionalities to nanoparticle assemblies, thus broadening the range of their applications.In this Account, we describe recent progress of our research groups in the development of new strategies for the self-assembly of nanoparticles tethered to macromolecules. At the beginning of our journey, we developed a new approach to patchy nanoparticles and their self-assembly. In a thermodynamically driven strategy, we used poor solvency conditions to induce homopolymer surface segregation in pinned micelles (patches). Patchy nanoparticles underwent self-assembly in a well-defined and controlled manner. Following this work, we overcame the limitation of low yield of the generation of patchy nanoparticles, by using block copolymer ligands. For block copolymer-capped nanoparticles, patch formation and self-assembly were "staged" by using distinct stimuli for each process. We expanded this work to the generation of patchy nanoparticles via dynamic exchange of block copolymer molecules between the nanoparticle surface and micelles in the solution. The scope of our work was further extended to a series of strategies that utilized the change in the configuration of block copolymer ligands during nanoparticle interactions. To this end, we explored the amphiphilicity of block copolymer-tethered nanoparticles and complementary interactions between reactive block copolymer ligands. Both approaches enabled exquisite control over directional and self-limiting self-assembly of complex hierarchical nanostructures. Next, we focused on the self-assembly of chiral nanostructures. To enable this goal, we attached chiral molecules to the surface of nanoparticles and organized these hybrid building blocks in ensembles with excellent chiroptical properties. In summary, our work enables surface engineering of polymer-capped nanoparticles and their controllable and predictable self-assembly. Future research in the field of nanoparticle self-assembly will include the development of effective characterization techniques, the synthesis of new functional polymers, and the development of environmentally responsive self-assembly of polymer-capped nanoparticles for the fabrication of nanomaterials with tailored functionalities.

Polymers as Versatile Players in the Stabilization, Capping, and Design of Inorganic Nanostructures

The integration of simple components to generate sophisticated hybrid materials with fine-tuned properties represents a significant scientific challenge. Herein, we present recent advances in the use of polymers to control the synthesis and properties of three of the most relevant inorganic nanoparticles, namely, quantum dots (QDs), magnetic nanoparticles (MNPs), and noble metal nanoparticles (NMNPs). We show relevant examples of how polymeric structures synthesized by techniques such as ATRP, RAFT, and living cationic polymerization are used to aid in the synthesis and stabilization of the nanostructures to generate nanocomposites with outstanding capabilities. Special emphasis is placed on describing how some of the exceptional physicochemical properties of polymers are used as nanoreactors to facilitate the synthesis of the nanostructure by providing an adequate chemical environment. Additionally, we also describe how polymers are utilized to protect the integrity of the nanostructure from chemical degradation. The integration of polymeric structures and the nanostructures has a strong impact on the dispersion and morphology of the latter and, consequently, endow them with novel and promising features. The advances described here, particularly the use of polymers to modulate and provide new properties to nanoparticles, exemplify the great versatility of polymers and how these may expand the capabilities of inorganic nanostructures that can be used to generate novel and sophisticated hybrid materials.

The impact of surface chemistry on the interfacial evaporation-driven self-assembly of thermoplasmonic gold nanoparticles

This paper reports an interfacial evaporation-driven approach for self-assembly of a gold nanoparticle (AuNP) film at the interface of liquid/air. We have designed colloidal plasmonic AuNPs capped with different types and surface coverage densities of ligands (i.e. purified and unpurified oleylamine-capped or thiol-protected AuNPs) and studied the impact of surface chemistry on the self-assembly of AuNPs using the optically excited plasmonic heating effect. By employing the extended DerjaguinLandau-Verwey-Overbeek model, the calculated lowest potential energies of the assembled AuNPs capped with purified oleylamine or alkyl thiols are between -1 k_BT and -2 k_BT, which is close to the room temperature thermal energy and represents a meta-stable assembly, indicating the reversible self-assembly of the AuNP film observed from the experiment. Furthermore, we observed the superheating phenomenon in well-dispersed nanoparticle solution while normal boiling occurred in the solutions with AuNP assemblies. The SERS activity of the as-prepared AuNP film has also been studied using rhodamine 6G as a molecular probe. This work not only provides a new aspect of the boiling phenomena of optically heated colloidal plasmonic nanoparticle solutions, but also provides inspiration for a new approach in designing surface ligands on the nanoparticles to realize reversible self-assembly via interfacial evaporation.

Synthesis of Janus Au@BCP nanoparticles via UV light-initiated RAFT polymerization-induced self-assembly

It is a great challenge to fabricate Janus inorganic/polymeric hybrid nanoparticles with both precisely controlled nanostructures and high yields. Herein, we report a new method to synthesize Janus Au@BCPs via UV light-initiated RAFT polymerization-induced self-assembly in situ at a high solid content. This strategy provides a promising alternative for achieving asymmetric hybrid nanoparticles with a controllable size, tunable morphology and convenient operation.