Shape and Color Switchable Block Copolymer Particles by Temperature and pH Dual Responses

Effect of Thermo- and pH-Sensitive Block Copolymer Structure and Composition on the Synthesis and Stabilization of Gold Nanoparticles

Homopolymers of poly[N-(2-(diethylamino)ethyl) acrylamide] exhibit the ability to adsorb onto the surface of preformed or growing gold nanoparticles. The resulting hybrid materials possess a pH and thermo-sensitive nature. Consequently, their optical properties can be modulated by manipulating either the temperature or the pH. Moreover, introducing monomers based on poly(N-isopropyl acrylamide) into block or random statistical polymers enables further modulation of the thermosensitive properties. These copolymers, employed for the in-situ synthesis and/or stabilization of gold nanoparticles, lead to hybrid materials whose properties and/or particle size depend on the polymer composition and microstructure: statistical polymers emerge as superior stabilizing agents compared to their block counterparts at a constant composition.

Dynamic Electrostatic Interfacial Engineering for Block Copolymer Microparticles with Reversible Structures

Responsive nanoparticle surfactants (NPSs) can dynamically and reversibly modulate the interfacial interactions between incompatible components, which are essential in the interfacial catalysis, corrosion, and self-assembly of block copolymers (BCPs). However, NPSs with stimuli-responsive behavior often involve tedious chemical synthesis and surface modifications. Herein, we propose a strategy to in situ construct a kind of dynamic and reversible NPSs by the interfacial electrostatic interaction between the negatively charged nanoparticles (NPs) and the positively charged homopolymers. The NPSs assembled at the oil/water interface reduce the interfacial tension and direct the confined assembly of BCP. Meanwhile, the dynamic NPSs can be disassembled by increasing the pH value or introducing competitive electrostatic attractions, which can dynamically and reversibly change the interfacial properties as well as the alignment of polymer chains, enabling BCP microparticles with reversibly switchable lamellar and cylindrical structures. Furthermore, by the introduction of aggregation-induced emission luminogens as tails to the NPSs, the reversible transformation of BCP microparticles can be visualized by fluorescence emission, which is dependent on the nanostructures of microparticles. This work establishes a concept for dynamically manipulating interfacial interactions and reversibly switching BCP microparticles without time-consuming NPS synthesis, showing promising applications in the fabrication of smart materials with switchable structures and properties.

Light-Responsive Shape- and Color-Changing Block Copolymer Particles with Fast Switching Speed

Polymer particles capable of dynamic shape changes in response to light have received substantial attention in the development of intelligent multifunctional materials. In this study, we develop a light-responsive block copolymer (BCP) particle system that exhibits fast and reversible shape and color transitions. The key molecular design is the integration of spiropyran photoacid (SPPA) molecules into the BCP particle system, which enables fast and dynamic transformations of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) particles in response to light. The SPPA photoisomerization, induced by 420 nm light irradiation, lowers the pH of the aqueous surroundings from 5.5 to 3.3. The protonated P4VP block substantially increases in domain size from 14 to 39 nm, resulting in significant elongation of the BCP particles (i.e., an increase in the aspect ratio (AR) of the particles from 1.8 to 3.4). Moreover, SPPA adsorbed onto the P4VP surface induces significant changes in the luminescent properties of the BCP particles via photoisomerization of SPPA. Notably, the BCP particles undergo fast, dynamic shape and color transitions within a period of 10 min, maintaining high reversibility over multiple light exposures. Functional dyes are selectively incorporated into different domains of the light-responsive BCP particles to achieve different ranges of color responses. Thus, this study showcases a light-responsive hydrogel display capable of reversible and multicolor photopatterning.

External field-driven property localization in liquids of responsive macromolecules

We explore theoretically the effects of external potentials on the spatial distribution of particle properties in a liquid of explicitly responsive macromolecules. In particular, we focus on the bistable particle size as a coarse-grained internal degree of freedom (DoF, or "property"), σ, that moves in a bimodal energy landscape, in order to model the response of a state-switching (big-to-small) macromolecular liquid to external stimuli. We employ a mean-field density functional theory (DFT) that provides the full inhomogeneous equilibrium distributions of a one-component model system of responsive colloids (RCs) interacting with a Gaussian pair potential. For systems confined between two parallel hard walls, we observe and rationalize a significant localization of the big particle state close to the walls, with pressures described by an exact RC wall theorem. Application of more complex external potentials, such as linear (gravitational), osmotic, and Hamaker potentials, promotes even stronger particle size segregation, in which macromolecules of different size are localized in different spatial regions. Importantly, we demonstrate how the degree of responsiveness of the particle size and its coupling to the external potential tune the position-dependent size distribution. The DFT predictions are corroborated by Brownian dynamics simulations. Our study highlights the fact that particle responsiveness can be used to localize liquid properties and therefore helps to control the property- and position-dependent function of macromolecules, e.g., in biomedical applications.

Fabrication of Hierarchical Assemblies through Temperature-Triggered Liquid Crystallization Driven Self-Assembly

Functional hierarchy is prevalent in biological systems owing to natural evolution. Efforts to replicate these structures in artificial materials have gained traction in materials science. Although artificial hierarchical structures are fabricated at different scales based on site-specific interactions using ABC-type block copolymers (BCPs), the fabrication of such hierarchical structures using AB-type BCPs via a simple and efficient method remains challenging. Herein, a class of amphiphilic BCPs (PDenm -b-PACholn ) is reported comprising dendronized oligoethylene glycol (Den) and cholesterol (AChol) as hydrophilic and hydrophobic moieties, respectively. By employing the collapse of PDenm blocks at a specific temperature, the fabrication of bundled fibers and multilayer vesicles is achieved with an obvious hierarchy. Different from common reversible aggregation-disaggregation processes of thermal-responsive polymers, the ordering of the core-forming block with liquid crystalline (LC) properties provides robustly physical cross-linking, coupled with epitaxial growth and the lateral fusion of LC blocks, guiding the formation of stable hierarchical micellar structures. It is highlighted that the combination of temperature-sensitive properties and LC ordering alignment offers a novel approach for constructing hierarchical structures using AB-type BCPs via an efficient one-step assembly method.

Tunable Structural Coloration in Eccentric Water-in-Oil-in-Water Droplets

Structural colors show diverse advantages such as fade resistance, eco-friendliness, iridescence, and high saturation in comparison with chemical pigments. In this paper, we show tunable structural coloration in colorless water-in-oil-in-water double emulsion droplets via total internal reflection and interference at the microscale concave interfaces. Through experimental work and simulations, we demonstrate that the shell thickness and the eccentricity of the core-shell structures are key to the successful formation of iridescent structural colors. Only eccentric thin-shell water-in-oil-in-water droplets show structural colors. Importantly, structural colors based on water-oil interfaces are readily responsive to a variety of environmental stimuli, such as osmotic pressure, temperature, magnetic fields, and light composition. This work highlights an alternative structural coloration that expands the applications of droplet-based structural colors to aqueous systems.

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.

The Process-Directed Self-Assembly of Block Copolymer Particles

The kinetic paths of structural evolution and formation of block copolymer (BCP) particles are explored using dynamic self-consistent field theory (DSCFT). It is shown that the process-directed self-assembly of BCP immersed in a poor solvent leads to the formation of striped ellipsoids, onion-like particles and double-spiral lamellar particles. The theory predicts a reversible path of shape transition between onion-like particles and striped ellipsoidal ones by regulating the temperature (related to the Flory-Huggins parameter between the two components of BCP, χAB ) and the selectivity of solvent toward one of the two BCP components. Furthermore, a kinetic path of shape transition from onion-like particles to double-spiral lamellar particles, and then back to onion-like particles is demonstrated. By investigating the inner-structural evolution of a BCP particle, it is identified that changing the intermediate bi-continuous structure into a layered one is crucial for the formation of striped ellipsoidal particles. Another interesting finding is that the formation of onion-like particles is characterized by a two-stage microphase separation. The first is induced by the solvent preference, and the second is controlled by the thermodynamics. The findings lead to an effective way of tailoring nanostructure of BCP particles for various industrial applications.

Sub-micron microparticles with tunable fluorescence emission obtained via co-self-assembly of amidoximed polymeric ligands and lanthanide ions

Lanthanide coordinating polymeric microparticles have witnessed increasing research interests during the past decades due to their versatile morphology and tunable fluorescent properties. Herein, we have synthesized an amidoximed block copolymer containing aromatic backbone and pendent amidoxime as well as carboxyl groups, which has been employed as the ligand to sensitize the intrinsic fluorescence emission of lanthanide ions of Tb³⁺ and Eu³⁺. Furthermore, the lanthanide coordinating polymeric microparticles showing tunable green and red emission fluorescence have been prepared via the emulsion confinement co-self-assembly of amidoximed polymeric ligands with Tb³⁺ and Eu³⁺. It is found that both the fluorescence emission and sizes of obtained fluorescent microparticles can be easily modulated in a wide range by tuning concentration of polymers and lanthanide ions, as well as emulsion evaporation temperature. Thanks to their tunable sizes (250-900 nm), fluorescence emission as well as presence of surface active functional groups, the present fluorescent microparticles would find potential applications in in-vitro detection, optical encoding and devices.

Light-adjusted supramolecular host-guest interfacial recognition for reconfiguring soft colloidal aggregates

The soft interfacial template-assisted confined self-assembly of block copolymers (BCPs) guiding colloidal aggregates has been extensively investigated by interfacial instability. Whether the macromolecular polymer architectonics possessed stimulus-responsive self-regulated structural controllability more readily implement the morphological diversity of colloidal aggregates. Herein, we in-situ constructed the alginate-modified β-cyclodextrin/azobenzene-functionalized alkyl chains (Alg-β-CD/AzoC12) system by supramolecular host-guest interfacial recognition-engineered strategy, in which possessed photo-stimulated responsive structural reconfigurability by modulating assembly/disassembly behaviors between CD and Azo at oil/water interface. The host-guest droplet interfaces acted as soft templates managing interfacial instability by synergistically integrating supra-amphiphilic host-guest polymers with cosurfactants, further constructing various soft supracolloidal aggregates, including soft nanoaggregates, microspheres with tunable degrees of surface roughness. Additionally, the stimuli-altering structural reconfigurability of supramolecular host-guest polymers was regulated by ultraviolet/visible irradiation, endowing soft aggregates with structural diversity. It's highly anticipated that the supramolecular host-guest interfacial recognition self-assembly establishes great bridge between supramolecular host-guest chemistry and colloid interface science.

Study of the phase-transition behavior of (AB)3 type star polystyrene-block-poly(n-butylacrylate) copolymers by the combination of rheology and SAXS

A series of three-armed star polystyrene-block-poly(n-butylacrylate) copolymers (PS-b-PBA)3 were synthesized to study the phase-transition behavior of the copolymers. The order-to-disorder transition temperature has been determined by oscillatory at different temperatures and dynamic temperature sweep at a fixed frequency. Moreover, the micro-phase separation in the block copolymers has been evaluated by time–temperature superposition, while the free volume and the active energy of the copolymers have been calculated. Interestingly, active energy decreased with the increase in the molecular weight of the PBA components. To further determine the order-to-disorder transition temperature precisely, small angle X-ray scattering was performed at different temperatures. These results confirm that the chain mobility of the star-shaped copolymers is strongly dependent on the arm molecular weight of the star polymers, which will be beneficial for the processing and material preparation of the block copolymers.

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.

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.

Active responsive colloids coupled to different thermostats

We introduce a model of active responsive colloids (ARCs) in which an internal degree of freedom (DoF) of a single colloidal particle is "activated" by coupling it to a different thermostat than for the translational DoFs. As for the responsive internal DoF, we consider specifically the size (diameter) of the spherical particles, which is confined by a harmonic parent potential being either entropic or energetic in nature. The ARCs interact via a repulsive Hertzian pair potential, appropriate to model hydrogels or elastic colloids, and are studied for various densities using Brownian dynamics simulations. We tune the internal activity in the nonequilibrium steady state by scanning through a wide range of internal temperatures, both smaller ("colder") and larger ("hotter") than the translational temperature. The results show a rich and intriguing behavior for the emergent property distributions, colloidal pair structure, and the diffusive translational dynamics controlled by the internal activity, substantially depending on whether the internal DoF moves in an entropic or energetic potential. We discuss theoretical thermal limits and phenomenological models which can explain some of the nonequilibrium trends qualitatively. Our study indicates that particle dynamical polydispersity as well as the structure and dynamics of dense macromolecular suspensions can be vastly tuned by internal activity in terms of internal "hot" or "cold" fluctuating states.

Noncovalent Postmodification Guided Reversible Compartmentalization of Polymeric Micelles

Compartmentalized micelles (CMs) are promising tailor-made soft matters that mimic natural designed structures and functions. Despite the structure of complex CMs, manipulating CM structures accessibly and reversibly remains elusive. Here, we report the fabrication of CMs via a generally valid noncovalent postmodification process. Starting from precursor micelles (PMs) based on one diblock copolymer, aromatic modification leads to the compartmentalization of PMs into well-defined spherical CMs. Control over compartment number, size and distribution in CMs, and segment distribution in their linear hierarchical assemblies is attained by simply tuning the postmodification degree and solvent composition. We also demonstrate the reversible transformation between PM and CMs during several heating-cooling cycles, which endows the micelles with potential in reversible functional transitions in situ close to nature's capability. Moreover, both hierarchically assembled or ill-structured micelles can rearrange into homogeneous CMs after one heating-cooling cycle, featuring the postmodification guided compartmentalization strategy with unprecedented micelle reproducibility.

Light-driven sequential shape transformation of block copolymer particles through three-dimensional confined self-assembly

Shape-controlled block copolymer (BCP) particles that respond to light stimulus have drawn great attention due to their promising applications in smart materials, yet polymeric particles with light-triggered controllable sequential shape transformation (SST) are still rarely reported. By confined co-assembly of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) and azo-containing light-responsive additives within emulsions, herein, we fabricated BCP particles with light-controlled SST behavior. Attributed to the quaternization of P2VP chains with bromoalkyl additives and the trans-cis isomerization of an azo group under UV light, the interfacial interactions between the BCPs and the surrounding aqueous phase are significantly varied; therefore, the particles exhibit three distinct phases in sequence: (1) elongation of ellipsoidal particles with increasing domain spacing; (2) shape transformation of elongated ellipsoidal particles into accordion-like particles; and (3) disassembly of polymer particles into small spheres. In addition, these particles with SST behavior can be used in light-controlled drug release at a high spatial-temporal resolution, demonstrating their potential in clinical settings and biomedicine.

Fabrication of pH/H2O2-responsive polyhedral oligomeric silsesquioxane self-assembled fluorescent vesicles for enhanced in vivo anti-tumor efficacy

Aim: The rational design of a fluorescence imaging-guided, highly efficient multiresponsive delivery system is important for improving drug delivery efficiency. Materials and methods: Herein, pH/H₂O₂-responsive polyhedral oligomeric silsesquioxane (POSS) molecule functionalized 4-(phenyl(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-phenyl)amino)benzaldehyde (OTB) copolymer (PEG-POSS-OTB) was synthesized to encapsulate doxorubicin (DOX) for precise drug delivery. Results: The self-assembly fluorescent vesicles exhibited excellent pH/H₂O₂-responsive drug release properties under physiological conditions and efficient drug-targeting ability. In vitro, compared with the DOX group, PEG-POSS-OTB fluorescent vesicles exhibited improved drug delivery and reduced toxicity. Importantly, we performed a proof-of-concept study demonstrating that PEG-POSS-OTB fluorescent vesicles were a high-efficiency nanoassembly drug-delivery platform for improving drug delivery efficiency. In vivo studies demonstrated that PEG-POSS-OTB vesicles with enhanced stability could be used in targeted drug delivery and controlled intelligent release.

Shaping Block Copolymer Microparticles by Positively Charged Polymeric Nanoparticles

Shape-transforming block copolymer (BCP) microparticles have attracted extensive attention due to their promising applications in nanotechnology, biomedicines, interfacial science, and other fields. As their performance is highly associated to their shape and structure, it is highly important to realize the precise control of particle shape. In this report, we propose a method to regulate the shape and structure of polystyrene-b-polydimethoxysiloxane (PS-b-PDMS) microparticles by using positively charged core-crosslinked nanoparticles (CNPs) as a co-surfactant, combining with cationic surfactant cetyltrimethylammonium bromide (CTAB). The electrostatic repulsive interactions between CNPs and CTAB dominate the shape of PS-b-PDMS particles. Upon introducing NaCl, the electrostatic repulsion is reduced, resulting in the reshape of PS-b-PDMS particles from striped Janus ellipsoids to onion-like microspheres at a critical concentration of NaCl (c_NaCl ). Interestingly, we find that the critical c_NaCl first increased then reached a plateau, as the increase in the crosslinking degree of the CNPs. Our work provides a simple strategy to tailor the morphology of BCPs by manipulating the electrostatic interaction. This article is protected by copyright. All rights reserved.

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.

Sensitive luminescence mechanochromism and unique luminescence thermochromism tuned by bending the P–O–P skeleton in the diphosphonium/iodocuprate(i) hybrid

The unique luminescence mechano/thermochromism of a diphosphonium/iodocuprate(i) hybrid is led by the mechanically induced adjustments in cuprophilic interactions and bent P–O–P backbone upon heating.

Shape-Changing Particles: From Materials Design and Mechanisms to Implementation

Demands for next-generation soft and responsive materials have sparked recent interest in the development of shape-changing particles and particle assemblies. Over the last two decades, a variety of mechanisms that drive shape change have been explored and integrated into particulate systems. Through a combination of top-down fabrication and bottom-up synthesis techniques, shape-morphing capabilities extend from the microscale to the nanoscale. Consequently, shape-morphing particles are rapidly emerging in a variety of contexts, including photonics, microfluidics, microrobotics, and biomedicine. Herein, the key mechanisms and materials that facilitate shape changes of microscale and nanoscale particles are discussed. Recent progress in the applications made possible by these particles is summarized, and perspectives on their promise and key open challenges in the field are discussed.

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...

Fast Photoswitchable Order-Disorder Transitions in Liquid-Crystalline Block Co-oligomers

Optically driven ordering transitions are rarely observed in macromolecular systems, often because of kinetic limitations. Here, we report a series of block co-oligomers (BCOs) that rapidly order and disorder at room temperature in response to optical illumination, and the absence thereof. The system is a triblock where rigid azobenzene (Azo) mesogens are attached to each end of a flexible siloxane chain. UV-induced trans-to-cis Azo isomerization, and vice versa in the absence of UV light, drive disordering and ordering of lamellar superstructures and smectic mesophases, as manifested by liquefaction and solidification of the material, respectively. The impacts of chemical structure on BCO self-assembly and photoswitching kinetics are explored by in situ microscopy and X-ray measurements for different mesogen end groups (NO₂ or CN), and different carbon chain lengths (0C or 12C) between the siloxane and the mesogen. The presence of the 12C spacer leads to hierarchical ordering with smectic layers of mesogens existing alongside larger length-scale lamellae, versus only smectic ordering without the spacer. These hierarchically ordered BCOs display highly persistent lamellar sheets that contrast with the tortuous, low-persistence "fingerprint"-type structures seen in conventional block copolymers. The reordering kinetics upon removal of UV illumination are extremely rapid (<5 s). This fast response is due to the electron-withdrawing NO₂ and CN, which facilitate cis-to-trans isomerization via thermal relaxation at room temperature without additional stimuli. This work elucidates structure-property relationships in photoswitching BCOs and advances the possibility of developing systems in which ordered nanostructures can be easily optically written and erased.

Switching microobjects from low to high aspect ratios using a shape-memory effect

Spherical particles from shape-memory polymers (SMP) can be stretched to ellipsoids with high aspect ratio (AR) and temporarily stabilized. They can switch back to low AR upon thermal stimulation. Here, the creation of an alternative shape-switching capability of particles from low to high AR is introduced, where a SMP matrix from polyvinyl alcohol (PVA) is used to create crosslinked high AR particles and to program the embedded micrometer-sized particles from a second SMP (oligo(ε-caprolactone) micronetworks, MN) with a low switching temperature T_sw. This programming proceeds through shape-recovery of the PVA matrix, from which the MN are harvested by PVA matrix dissolution. The use of a dissolvable SMP matrix may be a general strategy to efficiently create systems with complex moving capabilities.

Hierarchical superstructures assembled from pH-responsive gold nanoparticles in deformable emulsion droplets

Integrating stimuli-responsive nanoparticles (NPs) into shape-tunable hierarchical superstructures has emerged as a powerful way to fabricate smart materials. Here, we propose a robust strategy for the fabrication of sheet-like superlattices and hollow capsules by precisely tuning the interfacial tension of emulsion droplets containing pH-responsive gold nanoparticle building blocks, providing an efficient route to construct hierarchical superstructures with different applications.

Thermoresponsive Polymers Based on Tertiary Amine Moieties

Thermoresponsive polymers exhibiting unique reversible phase transition properties in aqueous solution in response to temperature stimuli have been extensively investigated. In the past two decades, thermoresponsive polymers based on tertiary amine moieties have achieved considerable progress and become an important family of thermoresponsive polymers, including tertiary amine functionalized poly((meth)acrylamide)s, poly((meth)acrylate)s, poly(styrene)s, poly(vinyl alcohol)s, and poly(ethylene oxide)s, which exhibit lower critical solution temperature and/or upper critical solution temperature in water or aliphatic alcohols. Their phase transition behavior can be modulated by the solution pH and CO₂ due to the protonation of tertiary amine moieties in acidic condition and deprotonation in alkaline condition and the charged ammonium bicarbonate formed by the tertiary amine moieties and CO₂ . The aim of this review is to summarize the recent progress in the thermoresponsive polymers based on tertiary amine moieties.

Morphology Transformation of Foldamer Assemblies Triggered by Single Oxygen Atom on Critical Residue Switch

The synthesis of morphologically well-defined peptidic materials via self-assembly is challenging but demanding for biocompatible functional materials. Moreover, switching morphology from a given shape to other predictable forms by molecular modification of the identical building block is an even more complicated subject because the self-assembly of flexible peptides is prone to diverge upon subtle structural change. To accomplish controllable morphology transformation, systematic self-assembly studies are performed using congener short β-peptide foldamers to find a minimal structural change that alters the self-assembled morphology. Introduction of oxygen-containing β-amino acid (ATFC) for subtle electronic perturbation on hydrophobic foldamer induces a previously inaccessible solid-state conformational split to generate the most susceptible modification site for morphology transformation of the foldamer assemblies. The site-dependent morphological switching power of ATFC is further demonstrated by dual substitution experiments and proven by crystallographic analyses. Stepwise morphology transformation is shown by modifying an identical foldamer scaffold. This study will guide in designing peptidic molecules from scratch to create complex and biofunctional assemblies with nonspherical shapes.

Photoswitchable Surfactant-Driven Reversible Shape- and Color-Changing Block Copolymer Particles

Polymer particles that switch their shape and color in response to light are of great interest for the development of programmable smart materials. Herein, we report block copolymer (BCP) particles with reversible shapes and colors activated by irradiation with ultraviolet (UV) and visible lights. This shape transformation of the BCP particles is achieved by a spiropyran-dodecyltrimethylammoium bromide (SP-DTAB) surfactant that changes its amphiphilicity upon photoisomerization. Under UV light (365 nm) irradiation, the hydrophilic ring-opened merocyanine form of the SP-DTAB surfactant affords the formation of spherical, onion-like BCP particles. In contrast, when exposed to visible light, surfactants with the ring-closed form yield prolate or oblate BCP ellipsoids with axially stacked nanostructures. Importantly, the change in BCP particle morphology between spheres and ellipsoids is reversible over multiple UV and visible light irradiation cycles. In addition, the shape- and color-switchable BCP particles are integrated to form a composite hydrogel, demonstrating their potential as high-resolution displays with reversible patterning capabilities.

Light-Enabled Reversible Shape Transformation of Block Copolymer Particles

Confined self-assembly of block copolymers (BCPs) is effective to manipulate various shapes of particles. In emulsion confined self-assembly, reversibly light-trigged switchable BCP particles are extremely expected, yet rarely reported. Herein, a novel strategy is developed to realize reversibly light-responsive shape-transformation of BCP particles by constructing functional surfactants with light-active azobenzene (azo) groups in the confined self-assembly of BCPs within emulsion droplet. Ultraviolet and visible lights can reversibly modulate the amphiphilicity and interfacial affinity of the surfactants to different blocks, triggering the reversible microphase structure transformation of BCP particles with high temporal-spatial resolution. We can realize shape and morphological transitions of BCP particles from onion-shaped spherical particles to striped ellipsoids and, ultimately, to inverse onion-like particles by ultraviolet irradiation. More importantly, this shape transformation is reversible by the irradiation of visible light, attributed to the reversible trans-cis isomerization of azo groups. We also demonstrate that the light-triggered shape transformation of BCP particles can be employed in a controllable drug release through a noncontacted and programmed manner, showing promising potential in clinic and biomedicine.

Fluorescence Switchable Block Copolymer Particles with Doubly Alternate-Layered Nanoparticle Arrays

The precise self-assembly of block copolymers (BCPs) and inorganic nanoparticles (NPs) under 3D confinement offers microparticles with programmable nanostructures and functionalities. Here, fluorescence-switchable hybrid microspheres are developed by forming doubly alternating arrays of Au NPs and CdSe/ZnS quantum dots (QDs) within polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) BCP domains. These doubly alternating arrays afford controlled nonradiative energy transfer (NRET) between the QDs and Au NPs that is dependent on the layer-to-layer distance. Solvent-selective swelling of the hybrid particles tunes the distance between layers, modulating their NRET behavior and affording switchable fluorescence. The particle fluorescence is "OFF" in water through strong NRET from the QDs to Au NPs, but is "ON" in alcohols due to the increased distance between the Au NP and QD arrays in the swollen P4VP domains. The experimentally observed NRET intensity as a function of interparticle distance shows larger quenching efficiencies than those theoretically predicted due to the enhanced quenching within a 3D-confined system. Finally, the robust and reversible fluorescence switching of the hybrid particles in different solvents is demonstrated, highlighting their potentials for bioimaging, sensing, and diagnostic applications.

Structure and dynamics of responsive colloids with dynamical polydispersity

Dynamical polydispersity in single-particle properties, for example a fluctuating particle size, shape, charge density, etc, is intrinsic to responsive colloids (RCs), such as biomacromolecules or microgels, but is typically not resolved in coarse-grained mesoscale simulations. Here, we present Brownian dynamics simulations of suspensions of RCs modeling soft hydrogel colloids, for which the size of the individual particles is an explicitly resolved (Gaussian) degree of freedom and dynamically responds to the local interacting environment. We calculate the liquid structure, emergent size distributions, long-time diffusion, and property (size) relaxation kinetics for a wide range of densities and intrinsic property relaxation times in the canonical ensemble. Comparison to interesting reference cases, such as conventional polydisperse suspensions with a frozen parent distribution, or conventional monodisperse systems interacting with an effective pair potential for one fixed size, shows a significant spread in the structure and dynamics. The differences, most apparent in the high density regimes, are due to many-body correlations and the dynamical coupling between property and translation in RC systems, not explicitly accounted for in the conventional treatments. In particular, the translational diffusion in the RC systems is surprisingly close to the free (single RC) diffusion, mainly due to a cancellation of crowding and size compression effects. We show that an effective monodisperse pair potential can be constructed that describes the many-body correlations reasonably well by convoluting the RC pair potential with the density-dependent emergent size distributions and using a mean effective diffusion constant.

Frustrated Microparticle Morphologies of a Semicrystalline Triblock Terpolymer in 3D Soft Confinement

Self-assembly of block copolymers (BCPs) in three-dimensional (3D) confinement of emulsion droplets has emerged as a versatile route for the formation of functional micro- and nanoparticles. While the self-assembly of amorphous coil-coil BCPs is fairly well documented, less is known about the behavior of crystalline-coil BCPs. Here, we demonstrate that confining a linear ABC triblock terpolymer with a crystallizable middle block in oil-in-water (O/W) emulsions results in a range of microparticles with frustrated inner structure originating from the conflict between crystallization and curved interfaces. Polystyrene-block-polyethylene-block-poly(methyl methacrylate) (PS-b-PE-b-PMMA, S₃₂E₃₆M₃₂⁹³) in toluene droplets was subjected to different preparation protocols. If evaporation was performed well above the bulk crystallization temperature of the PE block (T_evap > T_c), S₃₂E₃₆M₃₂⁹³ first microphase-separated into microparticles with lamella morphology followed by crystallization into a variety of frustrated morphologies (e.g., bud-like, double staircase, spherocone). By evaporating at significantly lower temperatures that allow the PE block to crystallize from solution (T_evap < T_c), S₃₂E₃₆M₃₂⁹³ underwent crystallization-driven self-assembly into patchy crystalline-core micelles, followed by confinement assembly into lenticular microparticles with compartmentalized hexagonal cylinder lattices. The frequency of these frustrated morphologies depends on polymer concentration and the evaporation protocol. These results provide a preliminary understanding of the morphological behavior of semicrystalline block copolymers in 3D soft confinement and may provide alternative routes to structure multicompartment microparticles from a broader range of polymer properties.

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.

Responsive Photonic Crystal Microcapsules of Block Copolymers with Enhanced Monochromaticity

Self-assembly of block copolymers (BCPs) has been developed as a promising approach for constructing photonic crystal (PC) microspheres for dynamic optical modulation. However, high curvature in the center of microspheres usually distorts the periodic core structure, leading to an inconsistency of photonic bandgap and poor monochromaticity of structural color. Herein, we report a simple yet robust strategy for fabricating responsive PC microcapsules of polystyrene-b-poly(2-vinylpyridine) through self-emulsification strategy. Interestingly, the microcapsules exhibit bright structural color with significantly enhanced monochromaticity, compared to their solid counterpart, since the microcapsules have no irregular cores. The structural colors of the PC microcapsules not only exhibit a variability through binary mixing of BCPs but also show a responsiveness to pH value. As a colored microcarrier, the PC microcapsules show a potential for visualizing the pH-dependent release behavior of encapsulated hydrophilic cargos on account of pH-responsive structural color.

Structure and position-dependent properties of inhomogeneous suspensions of responsive colloids

Responsive particles, such as biomacromolecules or hydrogels, display a broad and polymodal distribution of conformations and have thus the ability to change their properties (e.g., size, shape, charge density, etc.) substantially in response to external fields or to their local environment (e.g., mediated by cosolutes or pH). Here we discuss the basic statistical mechanics for a model of responsive colloids (RCs) by introducing an additional "property" degree of freedom as a collective variable in a formal coarse-graining procedure. The latter leads to an additional one-body term in the coarse-grained (CG) free energy, defining a single-particle property distribution for an individual polydisperse RC. We argue that in the equilibrium thermodynamic limit such a CG system of RCs behaves like a conventional polydisperse system of nonresponsive particles. We then illustrate the action of external fields, which impose local (position-dependent) property distributions leading to nontrivial effects on the spatial one-body property and density profiles, even for an ideal (noninteracting) gas of RCs. We finally apply density-functional theory in the local density approximation to discuss the effects of particle interactions for specific examples of (i) a suspension of RCs in an external field linear in both position and property, (ii) a suspension of RCs with highly localized properties (sizes) confined between two walls, and (iii) a two-component suspension where an inhomogeneously distributed (nonresponsive) cosolute component, as found, e.g., in the studies of osmolyte- or salt-induced collapse or swelling transitions of thermosensitive polymers, modifies the local properties and density of the RC liquid.

Fluorescent Polymer-MoS2-Embedded Microgels for Photothermal Heating and Colorimetric Monitoring

Photothermal heating with accurate monitoring of local temperature in complex biological fluids is crucial for therapeutic accuracy. Herein, photothermal microgels are developed to heat microscopic volumes through photothermal conversion and report the local temperature with a colorimetric response. The microgels consist of poly(ethylene glycol)-based hydrogels, which integrate temperature-responsive block-copolymer-grafted MoS₂ nanosheets (BCP-grafted MoS₂ NSs). The MoS₂ NSs are used as a fluorescence quencher as well as an efficient photothermal agent, with their surface decorated with three distinct temperature-responsive BCPs containing blue-, green-, and red-fluorescent dyes. Upon irradiation of near-infrared light, MoS₂ NSs convert the radiation into heat, and the BCPs change their conformation depending on the local temperature, selectively activating Förster resonance energy transfer of the three dyes. The use of three distinct BCPs and dyes enables the measurement of temperature in a wide range (i.e., from 25 to 50 °C). Importantly, the hydrogel matrix excludes molecules larger than the limiting mesh size so that BCP-grafted MoS₂ NSs remain free from contamination against large adhesive proteins such as albumin, thus maintaining their sensitivity even in complex fluids.

Converting Poly(Methyl Methacrylate) into a Triple-Responsive Polymer

Multiresponsive polymers that can respond to several external stimuli are promising materials for a manifold of applications. Herein, a facile method for the synthesis of triple-responsive (pH, temperature, CO2 ) poly(N,N-diethylaminoethyl methacrylamide) by a post-polymerization amidation of poly(methyl methacrylate) (PMMA) is presented. Combined with trivalent counterions ([Fe(CN)6 ]3- ) both an upper and lower critical solution temperature (UCST/LCST)-type phase behavior can be realized at pH 8 and 9. PMMA and PMMA-based block copolymers are readily accessible by living anionic and controlled radical polymerization techniques, which opens access to various responsive polymer architectures based on the developed functionalization method. This method can also be applied on melt-processed bulk PMMA samples to introduce functional, responsive moieties at the PMMA surface.

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.