Effect of Polymer Ligand Conformation on the Self-Assembly of Block Copolymers and Polymer-Grafted Nanoparticles within an Evaporative Emulsion

Icosahedral supracrystal assembly from polymer-grafted nanoparticles via interplay of interfacial energy and confinement effect

Self-assembly of nanoparticles (NPs) in drying emulsion droplets paves the way for intricate three-dimensional (3D) superstructures, given the myriad of control parameters for fine-tuning assembly conditions. With their substantial energetic dynamics that are acutely responsive to emulsion confinements, polymeric ligands incorporated into a system can enrich its structural diversity. Here, we demonstrate the assembly of soft polymer-grafted NPs into Mackay icosahedrons beyond spherical body-centered cubic (BCC) packing structures commonly observed for these soft spheres. This behavior is governed by the free energy minimization within emulsions through the interplay of the oil-water interfacial energy and confinement effect as demonstrated by the experimental observations of structural transitions between icosahedrons and BCC crystals and by corresponding free energy calculations. The anisotropic surface of the icosahedral supracrystals provides the capability of guiding the position of a secondary constituent, creating unique hybrid patchy icosahedrons with the potential to develop into multifunctional 3D clusters that combine the benefits of both polymers and conventional colloids.

Stimuli-responsive nanoparticle self-assembly at complex fluid interfaces: a new insight into dynamic surface chemistry

The self-assembly of core/shell nanoparticles (NPs) at fluid interfaces is a rapidly evolving area with tremendous potential in various fields, including biomedicine, display devices, catalysts, and sensors. This review provides an in-depth exploration of the current state-of-the-art in the programmed design of stimuli-responsive NP assemblies, with a specific focus on inorganic core/organic shell NPs below 100 nm for their responsive adsorption properties at fluid and polymer interfaces. The interface properties, such as ligands, charge, and surface chemistry, play a significant role in dictating the forces and energies governing both NP-NP and NP-hosting matrix interactions. We highlight the fundamental principles governing the reversible surface chemistry of NPs and present detailed experimental examples in the following three key aspects of stimuli-responsive NP assembly: (i) stimuli-driven assembly of NPs at the air/liquid interface, (ii) reversible NP assembly at the liquid/liquid interface, including films and Pickering emulsions, and (iii) hybrid NP assemblies at the polymer/polymer and polymer/water interfaces that exhibit stimuli-responsive behaviors. Finally, we address current challenges in existing approaches and offer a new perspective on the advances in this field.

The Effect of Colloidal Nanoparticles on Phase Separation of Block and Heteroarm Star Copolymers Confined between Polymer Brushes

The effect of colloidal nanoparticles on the phase changes of the amphiphilic AB linear diblock, A1A2B, and A2B heteroarm star copolymers confined between two polymer brush substrates was investigated by using a real-space self-consistent field theory. By changing the concentrations of nanoparticles and polymer brushes, the phase structure of the amphiphilic AB copolymer transforms from lamellar to core-shell hexagonal phase to cylinder phase. The pattern of A2B heteroarm star copolymer changes from core-shell hexagonal phases to lamellar phases and the layer decreases when increasing the density of the polymer brushes. The results showed that the phase behavior of the system is strongly influenced by the polymer brush architecture and the colloidal nanoparticle numbers. The colloidal nanoparticles and the soft confined surface of polymer brushes make amphiphilic AB copolymers easier to form ordered structures. The dispersion of the nanoparticles was also investigated in detail. The soft surfaces of polymer brushes and the conformation of the block copolymers work together to force the nanoparticles to disperse evenly. It will give helpful guidance for making some new functional materials by nano etching technology, nano photoresist, and nanoprinting.

Entropy-driven formation of binary superlattices assembled from polymer-tethered nanorods and nanospheres

Integrating binary mixtures of nanoparticles (NPs) into well-defined superstructures gives rise to novel collective properties depending on the shapes and individual properties of both species. In this paper, we studied the entropy-driven formation of binary superlattices assembled from polymer-tethered nanorods and nanospheres. The results indicated that the conformational entropy of the polymer chains and the mixing entropy of the nanorods and nanospheres are two parameters that determine the formation of binary superlattices.

Morphological Evolution of Hybrid Block Copolymer Particles: Toward Magnetic Responsive Particles

The co-assembly of block copolymers (BCPs) and inorganic nanoparticles (NPs) under emulsion confinement allows facile access to hybrid polymeric colloids with controlled hierarchical structures. Here, the effect of inorganic NPs on the structure of the hybrid BCP particles and the local distribution of NPs are studied, with a particular focus on comparing Au and Fe3O4 NPs. To focus on the effect of the NP core, Au and Fe3O4 NPs stabilized with oleyl ligands were synthesized, having a comparable diameter and grafting density. The confined co-assembly of symmetric polystyrene-b-poly(1,4-butadiene) (PS-b-PB) BCPs and NPs in evaporative emulsions resulted in particles with various morphologies including striped ellipsoids, onion-like particles, and their intermediates. The major difference in PS-b-PB/Au and PS-b-PB/Fe3O4 particles was found in the distribution of NPs inside the particles that affected the overall particle morphology. Au NPs were selectively localized inside PB domains with random distributions regardless of the particle morphology. Above the critical volume fraction, however, Au NPs induced the morphological transition of onion-like particles into ellipsoids by acting as an NP surfactant. For PS-b-PB/Fe3O4 ellipsoids, Fe3O4 NPs clustered and segregated to the particle/surrounding interface of the ellipsoids even at a low volume fraction, while Fe3O4 NPs were selectively localized in the middle of PB domains in a string-like pattern for PS-b-PB/Fe3O4 onion-like particles.

In Situ Self-Assembly of Nanoscale Particles into Macroscale Ordered Monolayers with Enhanced Memory Performance

In situ fabrication of macroscale ordered monolayers of nanoparticles (NPs) on targeted substrates is highly desirable for precision electronic and optical devices, while it remains a great challenge. In this study, a solution is provided to address this challenge by developing a colloidal ink formulation and employing the direct-ink-writing (DIW) technique, where on-demand delivery of ink at a targeted location and directional evaporation with controllable rate are leveraged to precisely guide the deposition of polystyrene-grafted gold NPs (Au@PS NPs) into a macroscale monolayer with an ordered Au NP array embedded in a PS thin film. A 2D steady-state diffusion-controlled evaporation model, which explains the parameter dependence of the experimental results and gives semiquantitative agreement with the experimental evaporation kinetics is proposed. The ordered monolayer is used as both nanocrystal floating gates and the tunneling layer for nonvolatile memory devices. It shows significantly enhanced performance compared with a disordered NP film prepared by spin coating. This approach allows for fine control of NP self-assembly to print macroscaleordered monolayers directly onto substrates, which has great promise for application in broad fields, including microelectronic and photoelectronic devices, sensors, and functional coatings.

Preparation of Photoswitchable Polyacrylic Nanocomposite Fibers Containing Au Nanorods and Spiropyran: Optical and Plasmonic Properties

Photoswitchable nanofibers and nanocomposite fibers containing plasmonic nanoparticles have attracted a great deal of interest in optical and plasmonic devices. Herein, photoswitchable poly(methyl methacrylate-co-vinylimidazole-co-spiropyran ethyl acrylate) (MVSP) and its copolymer with butyl acrylate (MBVSP) were prepared via emulsion polymerization, and the corresponding nanofibers (MVSP@NF and MBVSP@NF) and nanocomposite fibers (MVSP/Au@NF and MBVSP/Au@NF) containing AuNRs were fabricated through electrospinning. FTIR and ¹H NMR analyses confirmed the progress of the copolymerization reaction. The morphology of the prepared nanofibers containing AuNRs with an aspect ratio of 2.5 was identified by SEM and TEM techniques. The inclusion of vinylimidazole into the copolymer chains resulted in well-dispersed AuNRs. Photoisomerization studies revealed a higher photochromic efficiency for MBVSP@F (reflective intensity of 37.4%) with respect to MVSP@NF (reflective intensity of 62.5%) because of the greater flexibility of the chains. In addition, the presence of AuNRs in the nanocomposite fibers with high absorptivity intensified the photochromic properties for both samples. The polarization-dependent plasmonic band of AuNRs was switched between 650 and 634 nm through the photoisomerization of nonpolar SP to polar MC reversibly for MVSP/Au@NF. This displacement was just 4 nm for MBVSP/Au@NF, owing to the limited coupling between AuNRs and MC isomers. Besides, the capability of both nanocomposite fibers for reversible optical patterning was investigated by fast write-erase cycles. Enhanced photofatigue resistance in those fibers and the photomodulation of the plasmonic band of AuNRs using SP to MC isomerization revealed their promising potential for optical patterning and on-demand real-time plasmonic devices.

Self-Assembly of Homo-Polyarylene Ether Into Reactive Matrix for Fabrication of Hybrid Functional Microparticles

Emulsion confinement self-assembly of block copolymer has witnessed increasing research interest in the recent decade, but the post-functionalization and application of the resultant polymeric micro/nano-particles are still in their infancy. In this work, a super-engineering polyarylene ether containing pendent nitrile and carboxyl (PAE-NC) has been synthesized and converted into polymeric microparticles for macromolecular enrichment via emulsion confinement self-assembly and subsequent surface modification. Moreover, the encapsulation capacity of PAE-NC was evaluated using hydrophobic fluorescent quantum dots (QD) as a functional probe. Particularly, we found that both the as-synthesized PAE-NC and its hydrolyzed derivatives could be converted into microparticles via emulsion confinement self-assembly. Furthermore, the co-self-assembly of red-emitting QD and PAE-NC enables the phase transfer of hydrophobic QD into hydrophilic luminescent microparticles with the persisted fluorescence emission. Based on these results, the current PAE-NC would be served as a versatile and robust matrix to fabricate advanced microparticles or microcapsules for various applications.

Symmetry-Breaking and Self-Sorting in Block Copolymer-Based Multicomponent Nanocomposites

Co-assembly of inorganic nanoparticles (NPs) and nanostructured polymer matrix represents an intricate interplay of enthalpic or entropic forces. Particle size largely affects the phase behavior of the nanocomposite. Theoretical studies indicate that new morphologies would emerge when the particles become comparable to the soft matrix's size, but this has rarely been supported experimentally. By designing a multicomponent blend composed of NPs, block copolymer-based supramolecules, and small molecules, a 3-D ordered lattice beyond the native BCP's morphology was recently reported when the particle is larger than the microdomain of BCP. The blend can accommodate various formulation variables. In this paper, when the particle size equals the microdomain size, a symmetry-broken phase appears in a narrow range of particle sizes and compositions, which we named the "train track" structure. In this phase, the NPs aligned into a 3-D hexagonal lattice and packed asymmetrically along the c axis, making the projection of the ac and the bc plane resemble train tracks. Computational studies show that the broken symmetry reduces the polymer chain deformation and stabilizes the metastable hexagonally perforated lamellar morphology. Given the mobility of the multicomponent blend, the system shows a self-sorting behavior: segregating into two macroscopic phases with different nanostructures based on only a few nanometers NP size differences. Smaller NPs form "train track" morphology, while larger NPs form a "simple hexagon" structure, where the NPs take a symmetric hexagonal arrangement. Detailed structural evolution and simulation studies confirm the systematic-wide cooperativity across different components, indicating the strong self-regulation of the multicomponent system.

Uniform Nanorods with Regioselective Distribution of Inorganic Nanoparticles Templated by 2D Block Copolymer Nanosheets

The inorganic/organic hybrid materials with regioselective distribution of functional inorganic nanoparticles (NPs) have received constant interest attributed to fascinating integrated properties. However, there remains a formidable challenge in realizing the regioselective distribution of NPs for the specific hybrid nanorods. Herein, we report the construction of uniform core-shell hybrid nanorods with the regioselective distribution of inorganic NPs by selectively disassembling the prepared NPs/polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) hybrid nanosheets. Moreover, through precisely adjusting the parameters, such as complexation ability between the metal precursor and P4VP blocks, the protonation degree of P4VP blocks and complexation time, the NPs/polymer core-shell hybrid nanorod with the uniform distribution of NPs, and dumbbell-like hybrid nanorods with selective distribution of NPs at both ends can be obtained. This finding reveals a unique insight into the design of the anisotropic functional hybrid materials with the regioselective distribution of inorganic NPs.

Poly(vinylpyridine)-Containing Block Copolymers for Smart, Multicompartment Particles

Multicompartment particles generated by the self-assembly of block copolymers (BCPs) have received considerable attention due to their unique morphologies and functionalities. A class of important building blocks for multicomponent particles...

Diversifying Composition Leads to Hierarchical Composites with Design Flexibility and Structural Fidelity

Although significant progress has been made in the self-assembly of nanostructures, present successes heavily rely on precision in building block design, composition, and pair interactions. These requirements fundamentally limit our ability to synthesize macroscopic materials where the likelihood of impurity inclusion escalates and, more importantly, to access molecular-to-nanoscopic-to-microscopic-to-macroscopic hierarchies, since the types and compositions of building blocks vary at each stage. Inspired by biological blends and high-entropy alloys, we hypothesize that diversifying the blend's composition can overcome these limitations. Increasing the number of components increases mixing entropy, leading to the dispersion of different components and, as a result, enhances interphase miscibility, weakens the dependence on specific pair interactions, and enables long-range cooperativity. This hypothesis is validated in complex blends containing small molecules, block copolymer-based supramolecules, and nanoparticles/colloidal particles. Hierarchically structured composites can be obtained with formulation flexibility in the filler selection and blend composition. It is worth noting that, by adding small molecules, we can solve the size constraint that plagues traditional block copolymer/nanoparticle blends. Detailed characterization and simulation further confirm that each component is distributed to locally mediate unfavorable interactions, cooperatively mitigate composition fluctuations, and retain structural fidelity. Furthermore, the blends have sufficient mobility to access tunable microstructures without compromising the order of the nanostructure. Besides establishing a kinetically viable pathway to release current constraints in the composite design and to navigate uncertainties during structure formation over multiple length scales, the present study demonstrates that entropy-driven behaviors can be realized in systems beyond high-entropy alloys despite inherent differences between metal alloys and organic/inorganic hybrids.