ACS Macro Letters最新文献

Graft block copolymers have the potential to serve as universal compatibilizers for immiscible polymer blends, but their engineering is impeded by the lack of a theoretical framework explaining how the enhanced interfacial adhesion of the compatibilized system is impacted by molecular architecture. We address this problem via coarse-grained molecular dynamics simulations of the uniaxial elongation of a ternary system of AB graft copolymers adsorbed at an immiscible, glassy, A/B homopolymer interface. The resulting toughness data are explained by a model for the removal of interfacial crossings that reflects the more facile reptation of grafts relative to the trapped entanglements that constrain the backbone. The model predicts that the toughness should be approximately linear with respect to the geometric mean of total backbone and graft entanglements prior to elongation, consistent with the molecular dynamics simulations and thus providing a direct connection between the macroscopically observable toughness and the microscopic entanglement network.

This study demonstrates a strategy to control lattice symmetry in a polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer hybridized with a small fraction of NH₂-tethered Fe₃O₄ magnetic nanoparticles incorporated within the cylindrical PMMA microdomains. A low-intensity magnetic field (= 350 mT) was applied following large-amplitude oscillatory shear alignment, transforming the shear-aligned hexagonally packed cylinders (HEX) into centered rectangular cylinders (CR) stabilized through microdomain reorientation that relieved chain crowding and stretching of the PS blocks. In contrast, applying the magnetic field to unoriented HEX induced reorganization into lamellae aligned parallel to the field. The lamellar phase represented the thermodynamic equilibrium state, whereas the CR phase was a kinetically stabilized metastable structure governed by the prealigned framework. These findings highlight low-intensity magnetic manipulation as an effective “noncontact tweezer” for tuning lattice symmetry in block copolymers via the interplay of magnetic anisotropy and initial microdomain orientation.

Shape-memory effects and mechanochromic properties in soft materials have attracted significant attention due to their potential applications in biomedical engineering. Herein, we use a simple strategy to integrate these two properties into a single biocomposite material, which is achieved by embedding cellulose nanocrystals (CNCs) into the keratin matrix (which is intrinsically shape morphable). Via the evaporation-induced self-assembly process, CNCs self-organize into a chiral nematic crystal structure with a specific pitch and are stabilized within the keratin matrix by hydrogen bonds. The physical cross-linking effect of CNCs significantly improves extensibility, tensile strength, and shape-memory recovery. During the deformation of keratin composite films, structure color variation from dark black to bright blue is observed, resulting from the variation of the CNC helical pitch that selectively reflects different wavelengths of polarized light to exhibit iridescence. This work presents dual-functional biocomposites in an eco-friendly method, which can be used as high-strain optical sensors.

Stimuli-responsive polymer brushes enable the selective capture and release of oil droplets from an aqueous phase. We study pH-switchable poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) grafts on weakly and strongly oleophilic surfaces. Under basic conditions, PDMAEMA is neutral and collapses, absorbing oil; under acidic conditions, it becomes polycationic, extends, and expels the droplet. On a weakly oleophilic substrate, this mechanism releases 86% of the oil, but on a strongly oleophilic substrate, only 0.5% is expelled due to the substrate’s strong attraction. To overcome this, we design a block copolymer brush with a PDMAEMA top layer above a pH-insensitive, permanently cationic, water-swollen poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride) (PMETAC) cushion that blocks oil access to the substrate. Upon acidification, this architecture releases 99% of the oil, even from strongly oleophilic surfaces. Furthermore, although low grafting density compromises switchability for the homopolymer, the block brush retains efficient catch-and-release performance.

Fiber-reinforced polymer composites (FRPCs) are widely used in aerospace and lightweight automotive materials, and renewable energy due to their exceptional strength-to-weight ratio. Epoxy resins, the most common matrices in FRPCs, offer excellent mechanical performance but suffer from two major drawbacks: their thermoset nature makes composites unrecyclable, preventing fiber recovery, and their petroleum-derived origin raises environmental and sustainability concerns. In this work, we developed a biobased epoxy resin which incorporated dynamic covalent bonds, synthesized from l-malic acid and sorbitol polyglycidyl ether, and applied it to the fabrication of FRPCs. The resulting resin and its composites exhibited outstanding mechanical performance, comparable to or even surpassing those of conventional petroleum-based systems. More importantly, the reinforcing fibers (carbon and basalt fibers) were fully recovered through a solution-based process and reused to fabricate next-generation FRPCs without loss in mechanical performance. Furthermore, the recovered resin solution could be directly reused for photocuring-based 3D printing without additional purification or separation steps.

The development of recyclable thermoplastic materials derived from natural sources is crucial in addressing the global plastic pollution problem. Herein, we used natural cellulose as a raw material to prepare a series of cellulose thermoplastics that are easy to recycle and have adjustable properties and excellent toughness through a homogeneous etherification process. The introduction of ether groups significantly weakens the hydrogen bonding interactions between cellulose chains, thereby facilitating the thermal motion of these chains. By changing the chemical structure and amount of ether groups, the glass transition temperature of cellulose ethers can be adjusted in the range 95–173 °C, and thermoplastic processing can be realized at 180–250 °C. The tensile strength of the obtained cellulose thermoplastics can be adjusted in the range 5–60 MPa, and the elongation at break can be adjusted in the range 15%–70%, which is much higher than the toughness of the reported cellulose thermoplastic materials and meets the performance requirements of common plastics. Moreover, they have an excellent water resistance. Even after long-term immersion in a high-humidity environment and water, the tensile strength remains basically unchanged and the toughness is slightly improved. Cellulose thermoplastics can be processed into various plastic forms such as water cups, straws, packaging materials, and fibers through common thermoplastic processing methods. Such high-performance thermoplastics based on natural polymers are expected to be a promising candidate for sustainable plastic.

It is known that reversible–deactivation radical polymerization (RDRP) offers distinct advantages in preparing homogeneous gel network microstructures. However, flexibly regulating hydrogel network microstructures via RDRP remains a significant challenge. Herein, we fully leveraged the advantages of atom transfer radical polymerization (ATRP) in preparing well-defined polymers and uniform hydrogel networks and proposed a strategy to construct hydrogel structures with a controlled hierarchical network. This approach employs a presynthesized, well-defined telechelic bromide macroinitiator (via ATRP) to initiate the photoATRP of vinyl monomers and divinyl cross-linkers. A primary polymer network was first formed by the telechelic macroinitiator. Subsequently, the active chain-end sites initiated ATRP of small-molecule cross-linkers, thereby grafting a covalently linked secondary cross-linked network. In other words, we have embedded larger, uniformly sized pores within a smaller, homogeneous network structure. The size of these “macropores” can be tuned by adjusting the molecular weight of the macroinitiator. This hierarchical architecture endows the hydrogel with significantly altered swelling behavior and mechanical properties. Furthermore, by using carbon-dot-catalyzed aqueous photoATRP, this type of hydrogel with a controllable hierarchical structure can be fabricated via digital light processing (DLP) 3D printing technology. This work provides new insights into the regulation of the microstructure and macroscopic properties of hydrogel materials.

Molecular simulations demonstrate that the enthalpic softening of elastomeric nanocomposites upon heating can arise naturally from a Poisson’s ratio mismatch between elastomer and nanoparticle networks, providing a more parsimonious explanation for this phenomenon than the widely accepted interpretation based on glassy interparticle bridging. Despite a century of use, the mechanism of nanoparticle-driven mechanical reinforcement of elastomers is unresolved. A major hypothesis attributes it to glassy interparticle bridges, supported by an observed inversion of the variation of the modulus E(T) on heating – from entropic stiffening in elastomers to enthalpic softening in nanocomposites. Here, molecular simulations reveal that elastomer enthalpic softening can instead emerge from a competition over the preferred volumes between elastomer and nanoparticulate networks. A theory for this competition accounting for softening of the bulk modulus on heating predicts the simulated E(T) inversion, suggesting that reinforcement is driven by a volume-competition mechanism unique to cocontinuous systems of soft and rigid networks.

Thermoresponsive hydrogels, due to their reversible optical properties that change with temperature, hold great promise for applications in smart windows and wearable sensors. However, traditional strategies for modulating the lower or upper critical solution temperature (LCST/UCST) transition typically involve complex synthetic processes and struggle to control the transition temperature and transparency window width while also presenting a trade-off between transparency and mechanical properties. Here, we report a dual-responsive hydrogel (PNMN) constructed by dispersing poly(N-isopropylacrylamide) (PNIPAm) microgels within a poly(N-acryloylglycamide) (PNAGA) network. Ion-specific modulation provides a simple and reversible strategy to simultaneously regulate its transparency and mechanical properties. Using SO₄^2–, the transparency window (T_700nm > 50%) can be reduced from 22 to 7 °C, while using SCN^– expands it to 26 °C. Simultaneously, the mechanical state of this hydrogel can transition from soft/elastic to tough/energy-dissipating, exhibiting tensile strengths of 22–695 kPa and moduli of 15–387 kPa while maintaining flexibility at −20 °C. Spectroscopic analysis revealed that strongly hydrated ions enhance hydrogen bonding between ordered polymers, while weakly hydrated ions disrupt interchain bonds and promote solvation of the polymer with water. This work demonstrates a feasible method for synergistically modulating thermal responsiveness and mechanical strength, providing a pathway for developing multifunctional adaptive hydrogels for next-generation windows and wearable devices.

We report an orthogonal polymerization strategy integrating reversible addition–fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) to synthesize monodisperse surface-functional polymeric microspheres. ATRP initiator-functionalized macro-RAFT agents were employed in photoinitiated RAFT dispersion polymerization of methyl methacrylate (MMA) to yield uniform PMMA microspheres bearing ATRP initiators at the corona. Subsequent surface-initiated ATRP enabled the grafting of well-defined linear polymer chains, including poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), poly(N-isopropylacrylamide) (PNIPAM), poly(N,N-dimethylacrylamide) (PDMA), and poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA), without loss of particle uniformity. Incorporation of trithiocarbonate-containing comonomers via surface-initiated ATRP further allowed orthogonal surface-initiated RAFT polymerizations to generate graft copolymer architectures. This modular ATRP-RAFT approach affords precise control over the microsphere morphology and surface chemistry, providing a versatile platform for constructing functional polymeric microspheres for various applications.