ACS Macro Letters最新文献

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.

The morphology and crystallization behavior of imidazolium ionenes as crystalline polyelectrolytes, poly(alkylene imidazolium bis(trifluoromethanesulfonimide)) (PC_mIm-TFSI) with varying methylene units (m), were systematically investigated. PC_mIm-TFSI, with m ranging from two to six, demonstrated thermoplastic properties and formed spherulites upon melt crystallization. The melting point (T_m) and radial growth rate of the spherulites (G) exhibited a marked dependence in the value of m, with T_m decreasing by approximately 40 °C, and the maximum values of G reducing to one-tenth or less as increased by one unit. An even–odd effect was observed in T_m, where the curve connecting T_m for odd m was lower than that for even m. Raman spectral imaging indicated that both the long axes of the polymer cations and the TFSI anions were tangentially aligned within the spherulites of all examined PC_mIm-TFSI. Blends of imidazolium ionenes with varying m or counteranions (TFSI^– or Br^–) exhibited diverse higher-order morphologies owing to segregation during crystallization. Immersion of a blended film composed of PC₃Im-TFSI and PC₃Im-Br in water led to the formation of pores owing to the differential water solubility of the segregated spherulites.

The formation of the helical phase from the self-assembly of chiral diblock copolymers is attributed to the twisting and shifting of the microphase-separated domain. With the introduction of midblock in-between achiral and chiral blocks, the mechanism of twisting and shifting would be steered by the capability of cross-domain chirality transfer from the chiral block. This work aims to systematically investigate the cross-domain chirality transfer by synthesizing a variety of chiral diblock copolymers, polystyrene-block-poly(l-lactide) (PS-b-PLLA), with various midblocks including poly(d,l-lactide) (PLA), poly(ethylene oxide) (PEO), polycaprolactone (PCL), poly(4-vinylpyridine) (P4VP), poly(4-chlorostyrene) (P4CS) and poly(methyl methacrylate) (PMMA). The capability of the cross-domain chirality transfer is found to be dependent upon the interaction parameter of the midblock and chiral block but less affected by the interaction parameter of the midblock and achiral block. With the increase of the interaction parameter, the driving force for the cross-domain chirality transfer will deteriorate, resulting in a smaller cross-domain distance for chirality transfer.

We engineer composites of biological DNA and synthetic sodium poly(styrenesulfonate) polymers with judiciously matched physical properties that interpenetrate to form miscible solutions spanning from semidilute to entangled regimes at varying DNA fractions w_DNA and ionic strengths I. The DNA entanglement concentration robustly dictates the crossover from semidilute to entangled dynamics for all compositions and ionic strengths of composites (w_DNA > 0). The effect of I emerges in the concentration dependence of viscosity, which transitions from polyelectrolyte scaling to good solvent scaling for neutral polymers as w_DNA and I increase. Conversely, the dynamics at shorter spatiotemporal scales follow θ-solvent scaling. Thus, combining biological and synthetic polyelectrolytes enables independent tuning of the polyelectrolyte fingerprint, entanglement concentration, and solvent interactions, which can be leveraged for engineering miscible polymer composites with greater dynamic range and responsiveness for applications from energy storage to drug delivery.

Excessive ultraviolet (UV) radiation poses significant adverse health effects on humans, underscoring the critical need for novel sunscreen agents. Conventional small-molecule UV filters often suffer from drawbacks such as percutaneous absorption and environmental toxicity. In this work, we report the design and synthesis of novel monomers bearing both dihydropyrimidin-2(1H)-thione (DHPMT) and dihydrothiazole moieties through the integration of the Biginelli reaction and sequential C–S coupling reaction, followed by the copolymerization with poly(ethylene glycol) methyl ether methacrylate (PEGMA-950) to yield new functional polymers. The resulting polymers exhibited low cytotoxicity. Importantly, in vivo evaluation in a murine model demonstrated their effective protection against UV-induced skin damage. This work underscores the synthetic versatility of this two-step reaction in the development of UV-shielding polymeric materials and offers a promising strategy for engineering multifunctional polymers via multicomponent reaction platforms.

Polymer adhesion on solids is governed by chain aggregation at interfaces, yet isolating intrinsic adhesion strength (G₀) from complex failure modes has remained elusive. Here, a surface and interfacial cutting analysis system (SAICAS) was used to quantify G₀ from thickness-dependent measurements. Polystyrene films with varied molecular weights and poly(methyl methacrylate) with different stereoregularities were analyzed as a function of thermal annealing time. G₀ increased with the growth of the adsorbed layer. At extended annealing times, absolute G₀ was dictated not by molecular weight but by segment-substrate interaction energy and chain conformation influenced by stereoregularity. These findings establish that interfacial adhesion is determined primarily by the total interaction energy from chain contact points with the solid. This study provides molecular-level insights into polymer adhesion and principles for the rational design of high-performance adhesives across applications.

The spreading and wetting of liquids on surfaces are ubiquitous in nature and industrial applications. Conventionally, highly viscous macromolecular fluids (e.g., honey and silicone oils) are hard to spread on various surfaces compared to low viscous fluids, such as water, due to strong viscous resistance at the interface. In this study, we report an opposite phenomenon that highly viscous fluids enriched in poly(ethylene glycol) (PEG) spread over substantially larger areas on immiscible, phase-separated aqueous interfaces than their low-viscosity counterparts. These aqueous interfaces are formed through the liquid–liquid phase separation between PEG of different molecular weights and sodium citrate salts or dextran. Experiments and scaling analysis reveal that this enhanced spreading arises from interfacial tension gradients between the two immiscible aqueous phases, with the spreading capability of fluids quantitatively characterized by the spreading coefficient. Furthermore, we demonstrate that these interfacial gradients arise from the asymmetric partitioning of PEG and its surfactant-like effect in reducing liquid–air interfacial tensions. Together, our work illustrates how macromolecular phase separation could facilitate the spreading of highly viscous fluids, with crucial implications for intracellular liquid–liquid phase separation and various industrial applications.

Both polymer size and chain elasticity depend on long-range bond correlations, which determine the chain Kuhn length. These correlations are gradually cut off with increasing externally applied force or polymer confinement, thereby decreasing the effective Kuhn length. We develop a theory for the strain-dependent Kuhn length and validate it with simulations. Our model explains why the Kuhn length obtained from single-molecule force spectroscopy experiments is smaller than the Kuhn length determined from scattering measurements of unperturbed chains. Finally, we propose a crossover function for the Kuhn length as a function of applied force, which can be used for the interpretation of force–extension curves.