Bifunctional additive-driven shape transitions of block copolymer particles through synergistic quaternization and protonation

Block copolymer (BCP) particles with tailored shapes and nanostructures hold promise for applications in cell adhesion, photonic system, and energy storage due to their unique optical and rheological properties. Conventional approaches relying on surfactant-mediated self-assembly often limit particle geometries to simple structures. Herein, we present a versatile approach to expand the morphology of poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) BCP particles through the incorporation of 9-bromononanoic acid (BNA), a bifunctional additive that facilitates synergistic quaternization and protonation. Increasing the BNA-to-2VP molar ratio enhances P2VP hydrophilicity and decreases the pH value, driving dramatic shape transitions from onion-like spheres to tulip bulbs, ellipsoids, discs, and Janus cups. This morphological diversity is attributed to synergetic interfacial instability-driven water infiltration and pH-induced repulsion of protonated P2VP chains. Additives with a single functional group, however, yield limited morphologies, such as tulip bulbs or onion-like spheres. Notably, Janus cups fabricated via this strategy exhibit selective cargo-loading capabilities, highlighting the importance of precise control over the internal composition and structure of BCP particles.

Neutral Interface Directed 3D Confined Self-Assembly of Block Copolymer: Anisotropic Patterned Particles with Ordered Structures

Three-dimensional confined self-assembly (3D-CSA) of block copolymers (BCPs) is a distinctive and robust strategy that can yield colloidal polymer particles boasting ordered internal structures and diverse morphologies. The unique advantage of neutral interface lies in its ability to create anisotropic particles with surface patterns. The resulting unique polymer particles exhibit deformability under swelling, coupled with excellent spreadability and optical properties. These particles can also be used for fabrication of anisotropic nanoobjects or mesoporous particles via disassembly or serving as templates. This review comprehensively outlines the research advancements in neutral interface-guided 3D-CSA systems, including surfactant engineering, internal structure control, properties and future possibilities of anisotropic patterned particles.

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.

Formation and Transformation of Polystyrene-block-poly(2-vinylpyridine) Hexasomes in the Solvent Exchange

The generation of inverse micellar nanostructures, especially those with open channels, using commercially available diblock copolymers (BCP), is vital for their wide applications in drug delivery and catalyst templating. However, the rigid requirements for forming inverse morphologies, such as the highly asymmetric molecular structures, the semicrystalline motifs, and concentrated solutions of diblock copolymers, represent obstacles to the development of successful strategies. In this study, the inverse polystyrene-block-poly(2-vinylpyridine) (PS_30K-b-P2VP_8.5K) micelles, i.e., the hexasomes with p6mm lattice, were generated through a modified solvent exchange via adding d-tartaric acid (d-TA) in the nonsolvent. Various intermediate morphologies have been identified with the change of d-TA concentration. Interestingly, in the high d-TA concentration (∼20 mg/mL), the hexasomes with close-packed hoops changed to mesoporous spheres with regularly packed perpendicular cylindrical channels (V_D-TA: V_BCP 6:100), and further to the mesoporous spheres with gyri-like open pores (V_D-TA: V_BCP > 15:100) with the increasing acidity in the mixed solvent. This study presents a simple and economical pathway for fabricating PS_30K-b-P2VP_8.5K hexasomes and first demonstrates these hexasomes can be modified to the morphology with open channels that will benefit their further applications.

Regioselective Seeded Polymerization in Block Copolymer Nanoparticles: Post-Assembly Control of Colloidal Features

Post-assembly modifications are efficient tools to adjust colloidal features of block copolymer (BCP) particles. However, existing methods often address particle shape, morphology, and chemical functionality individually. For simultaneous control, we transferred the concept of seeded polymerization to phase separated BCP particles. Key to our approach is the regioselective polymerization of (functional) monomers inside specific BCP domains. This was demonstrated in striped PS-b-P2VP ellipsoids. Here, polymerization of styrene preferably occurs in PS domains and increases PS lamellar thickness up to 5-fold. The resulting asymmetric lamellar morphology also changes the particle shape, i.e., increases the aspect ratio. Using 4-vinylbenzyl azide as co-monomer, azides as chemical functionalities can be added selectively to the PS domains. Overall, our simple and versatile method gives access to various multifunctional BCP colloids from a single batch of pre-formed particles.

Solvent Annealing of Striped Ellipsoidal Block Copolymer Particles: Reversible Control over Lamellae Asymmetry, Aspect Ratio, and Particle Surface

Solvent annealing is a versatile tool to adjust the shape and morphology of block copolymer (BCP) particles. During this process, polar solvents are often used for block-selective swelling. However, such water-miscible solvents can induce (partial) solubilization of one block in the surrounding aqueous medium, thus, causing complex structural variations and even particle disassembly. To reduce the complexity in morphology control, we focused on toluene as a nonpolar polystyrene-selective solvent for the annealing of striped polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) ellipsoids. The selective stretching of PS chains produces unique asymmetric lamellae structures, which translate to an increase in the particle aspect ratio after toluene evaporation. Complete reversibility is achieved by changing to chloroform as a nonselective solvent. Moreover, surfactants can be used to tune block-selective wetting of the particle surface during the annealing; for example, a PS shell can protect the internal lamellae structure from disassembly. Overall, this versatile postassembly process enables the tailoring of the structural features of striped colloidal ellipsoids by only using commercial BCPs and solvents.

Responsive Nanostructured Polymer Particles

Responsive polymer particles with switchable properties are of great importance for designing smart materials in various applications. Recently, the self-assembly of block copolymers (BCPs) and polymer blends within evaporative emulsions has led to advances in the shape-controlled synthesis of polymer particles. Despite extensive recent progress on BCP particles, the responsive shape tuning of BCP particles and their applications have received little attention. This review provides a brief overview of recent approaches to developing non-spherical polymer particles from soft evaporative emulsions based on the physical principles affecting both particle shape and inner structure. Special attention is paid to the stimuli-responsive, shape-changing nanostructured polymer particles, i.e., design of polymers and surfactant pairs, detailed experimental results, and their applications, including the state-of-the-art progress in this field. Finally, the perspectives on current challenges and future directions in this research field are presented, including the development of surfactants with higher reversibility to multiple stimuli and polymers with unique structural functionality, and diversification of polymer architectures.

Shaping Block Copolymer Microparticles by pH-Responsive Core-Cross-Linked Polymeric Nanoparticles

Block copolymer microparticles with controllable morphology have drawn widespread attention owing to their promising applications in photonic materials, energy storage, and other areas. Hence, it is highly desired to achieve a controllable transformation of microparticle morphology. In this work, we report a simple method to shape the morphology of polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) microparticles, by employing core-cross-linked polymeric nanoparticles (CNPs) as cosurfactants which are synthesized through cross-linking P4VP segment of PS-block-poly(4-vinylpyridine) (PS-b-P4VP). The addition of pH-responsive CNPs makes the shape of pH-inert PS-b-PDMS microparticles sensitive to pH value. The PS-b-PDMS microparticles transformed from elongated Janus pupa-like particles to onion-like particles by decreasing the pH value of the aqueous phase. The deformation mechanism is investigated by changing pH value, the weight fraction of CNPs, and surfactant property. This study provides a facile strategy to deform microparticles of pH-inert BCPs by tuning pH value, which is anticipated to be applicable to other non-pH-responsive BCP microparticles.

Transformable Colloidal Polymer Particles with Ordered Internal Structures

Based on studies combining experiments and simulations, internally ordered colloidal particles that are able to undergo morphological transformations both in shape and internal structure are presented. The particles are prepared by emulsion solvent evaporation-induced 3D soft confined assembly of di-block copolymer polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP). Control over the solvent selectivity leads to a dramatic change in shape and internal structure for particles. Pupa-like particles of lamellar morphology are obtained when using a non-selective solvent, while patchy particles possessing a plum pudding structure formed when the solvent is selective for PS-block. More interestingly, 3D soft confined annealing drives order-order morphological transformation of the particles. The morphology of reshaped particles can be well controlled by varying the solvent selectivity, annealing time, and interfacial interaction. The experimental results can be explained based on simulations. This study can offer considerable scope for the design of new stimuli-responsive colloidal particles for potential applications in photonic crystal, drug delivery and release, sensor and smart coating, etc.

Effect of Site-Specific Functionalization on the Shape of Nonspherical Block Copolymer Particles

Shape-anisotropic polymeric colloids having chemically distinct compartments are promising materials, however, introducing site-specific surface functionality to block copolymer (BCP) particles has not yet been actively investigated. The current contribution demonstrates the selective surface functionalization of nanostructured, ellipsoidal polystyrene-b-polybutadiene (PS-b-PB) particle and investigate their effects on the particle shape. Photo-induced thiol-ene click reaction was used as a selective functionalization chemistry for modifying the PB block, which was achieved by controlling the feed ratio of functional thiols to the double bonds in PB. Importantly, the controlled particle elongation was observed as a function of the degree of PB functionalization. Such an increase in the aspect ratio is attributed to the (i) increased incompatibility of the PS and modified PB block and (ii) the reduced surface tension between the particles and surrounding aqueous medium, both of which contributes to the further elongation of ellipsoids. Further tunability of the elongation behavior of ellipsoids was further demonstrated by controlling the particle size and chemical structure of functional thiols, showing the versatility of this approach for controlling the particle shape. Finally, the utility of surface functionality was demonstrated by the facile complexation of fluorescent dye on the modified surface of the particle via favorable interaction, which showed stable fluorescence and colloidal dispersity.

100th Anniversary of Macromolecular Science Viewpoint: Block Copolymer Particles: Tuning Shape, Interfaces, and Morphology

Confined assembly of block copolymers (BCPs) is receiving increasing attention due to the ability to create unconventional morphologies that cannot be observed in the corresponding bulk systems. This effect is further driven by the simplicity and versatility of these procedures for controlling the shape of particles prepared by 3D soft confinement of BCPs in emulsions. By taking advantage of a mobile emulsion interface, the one-step formation of nonspherical BCP particles through spontaneous deformation is possible with design principles and theoretical models for controlling shape/nanostructure now being established. This Viewpoint highlights strategies for shape tuning of BCP particles, currently accessible shapes, their controllability, and potential application. The emergence of 3D soft confinement of BCPs and related theory is overviewed with a focus on current strategies, types of nonspherical shapes achieved, and structure-property relationships for nonspherical BCP particles. Finally, the applications and future perspectives for these materials are discussed.

Probing the morphology evolution of chemically anisotropic colloids prepared by homopolymerization- and copolymerization-induced phase separation

Chemically anisotropic colloids prepared by polymerization-induced phase separation during seeded emulsion polymerization with non-crosslinked seeds reveals tunability in both surface and interior properties based on the morphology evolution.

Formation Mechanisms of Porous Particles from Self-Assembly of Amphiphilic Diblock Copolymers inside an Oil-in-Water Emulsion Droplet upon Solvent Evaporation

The formation mechanisms of porous particles from self-assembly of amphiphilic diblock copolymers inside an oil-in-water emulsion droplet upon evaporation of the organic solvent are investigated based on Monte Carlo simulations for the first time. A morphological diagram of particles is constructed as a function of the surfactant concentration (φ) and the copolymer composition characterized by the volume fraction of the hydrophilic B block ( f_B). Particles with various morphologies are predicted. Morphological sequences from non-porosity to closed-porosity to capsules and finally to open-porosity particles are usually observed with increasing φ when f_B ≤ 1/2, with the only exception that capsules do not occur when f_B = 1/6. Furthermore, the critical φ value for a given morphological transition usually decreases with increasing f_B. Micelles are always observed at higher φ regions when f_B > 1/2. It is found that the specific surface area falls on almost the same regime for particles with the same kind of morphology, indicating that the morphology of a particle largely determines its specific surface area. The chain stretching varies with the particle morphology. It is the presence of the surfactant that makes the formation of porous particles possible, while when φ > 0, multiple morphological transitions can be induced by changing f_B. In the process of organic solvent removal, the value of f_B may affect the shape of pores inside the droplet and hence leads to the f_B dependence of the morphological sequences. When the solvent evaporation is not too fast, the resulting morphological sequence does not depend on the evaporation rate. Our results are compared with related experiments.

Tannic Acid-Mediated Aggregate Stabilization of Poly(N-vinylpyrrolidone)-b-poly(oligo (ethylene glycol) methyl ether methacrylate) Double Hydrophilic Block Copolymers

The self-assembly of block copolymers in aqueous solution is an important field in modern polymer science that has been extended to double hydrophilic block copolymers (DHBC) in recent years. In here, a significant improvement of the self-assembly process of DHBC in aqueous solution by utilizing a linear-brush macromolecular architecture is presented. The improved self-assembly behavior of poly(N-vinylpyrrolidone)-b-poly(oligo(ethylene glycol) methyl ether methacrylate) (PVP-b-P(OEGMA)) and its concentration dependency is investigated via dynamic light scattering (DLS) (apparent hydrodynamic radii ≈ 100-120 nm). Moreover, the DHBC assemblies can be non-covalently crosslinked with tannic acid via hydrogen bonding, which leads to the formation of small aggregates as well (apparent hydrodynamic radius ≈ 15 nm). Non-covalent crosslinking improves the self-assembly and stabilizes the aggregates upon dilution, reducing the concentration dependency of aggregate self-assembly. Additionally, the non-covalent aggregates can be disassembled in basic media. The presence of aggregates was studied via cryogenic scanning electron microscopy (cryo-SEM) and DLS before and after non-covalent crosslinking. Furthermore, analytical ultracentrifugation of the formed aggregate structures was performed, clearly showing the existence of polymer assemblies, particularly after non-covalent crosslinking. In summary, we report on the completely hydrophilic self-assembled structures in solution formed from fully biocompatible building entities in water.

Using Synergistic Multiple Dynamic Bonds to Construct Polymers with Engineered Properties

Dynamic bonds have achieved significant attention for their ability to impart fascinating properties to polymeric materials, such as high mechanical strength, self-healing, shape memory, 3D printability, and conductivity. Incorporating multiple dynamic bonds into polymer systems affords an attractive and efficient approach to endow multiple functionalities. This mini-review focuses on the use of complementary dynamic interactions to control the properties of soft materials. Owing to the diversity in dynamic chemistries that can be explored, the scope of this article is restricted to polymers and does not include colloids, amphiphiles, liquid crystals, or biological soft matter.

Shape control of nanostructured cone-shaped particles by tuning the blend morphology of A-b-B diblock copolymers and C-type copolymers within emulsion droplets

An approach to blend AB-type block copolymers and C-type copolymers within the emulsion droplet is an efficient particle shape-engineering strategy.

Polyphilicity-An Extension of the Concept of Amphiphilicity in Polymers

Recent developments in synthetic pathways as simple reversible-deactivation radical polymerization (RDRP) techniques and quantitative post-polymerization reactions, most notoriously 'click' reactions, leading to segmented copolymers, have broadened the molecular architectures accessible to polymer chemists as a matter of routine. Segments can be blocks, grafted chains, branchings, telechelic end-groups, covalently attached nanoparticles, nanodomains in networks, even sequences of random copolymers, and so on. In this review, we describe the variety of the segmented synthetic copolymers landscape from the point of view of their chemical affinity, or synonymous philicity, in bulk or with their surroundings, such as solvents, permeant gases, and solid surfaces. We focus on recent contributions, current trends, and perspectives regarding polyphilic copolymers, which have, in addition to hydrophilic and lipophilic segments, other philicities, for example, towards solvents, fluorophilic entities, ions, silicones, metals, nanoparticles, and liquid crystalline moieties.