Soft Matter最新文献

Filler-hydrogel composites combine enhanced mechanical properties with functionalities conferred by the nanofillers. When the nanofillers interact attractively with the hydrogel matrix, even low nanofiller volume fractions can lead to a strong increase in the linear viscoelastic moduli. Here, we build on our understanding of the microscopic phenomena at play in these systems to explore their nonlinear response, using attractive nanofillers embedded in a gelatin matrix. We identify a critical deformation beyond which the material no longer recovers its macroscopic viscoelastic properties, marking the onset of macroscopic irreversibility. Increasing nanofiller volume fraction leads to nanofiller-induced stiffening of the polymer matrix, yet the overall viscoelastic response of the composites remains qualitatively similar to that of pure hydrogels: under increasing strain amplitude, their elastic and viscous moduli, G' and G″, exhibit a pronounced overshoot followed by a crossover associated with yielding. A transition occurs in the composite at the strain amplitude where G' reaches its maximum, characterized by a marked change in the stress relaxation dynamics. Beyond , the composites no longer recover their initial viscoelastic properties in repeated strain amplitude sweeps, indicating that the material has sustained macroscopically irreversible changes and a permanent loss of elasticity. We thus identify three distinct regimes in the strain-stiffening materials: nonlinear elasticity, macroscopic irreversibility, and yielding. We further suggest that the plasticity underpinning macroscopic irreversibility is due to the breaking of bonds that contribute most to the composite's strain stiffening response in the hydrogel matrix.

We experimentally investigate how drying history influences microparticle-substrate adhesion in hydrophilic systems. By systematically varying air temperature, relative humidity, and drying duration under controlled conditions, we quantify the detachment force of individual microparticles. Air temperature emerges as the dominant factor: higher temperatures and lower humidity enhance adhesion, while prolonged drying generally reduces it, except under combined high-temperature and low-humidity conditions, where strong adhesion persists. Complementary scanning electron microscopy (SEM) results reveal drying-time-dependent changes in the particle-substrate contact size, consistent with capillary-induced compression of the contact zone followed by partial relaxation. These findings indicate that transient capillary stresses during evaporation deform the particle-substrate interface and leave a lasting imprint on adhesion strength. Overall, the study shows how capillarity, drying dynamics, and contact mechanics couple to regulate adhesion in colloidal systems, offering new insights into particle-substrate interactions in soft matter contexts.

In hydrodynamic descriptions of lipid bilayers, the membrane is often approximated as being impermeable to the surrounding, solute-containing fluid. However, biological and in vitro lipid membranes are influenced by their permeability and the resultant osmotic forces-whose effects remain poorly understood. Here, we study the dynamics of a fluctuating, planar lipid membrane that is ideally selective: fluid can pass through it, while solutes cannot. We find that the canonical membrane relaxation mode, in which internal membrane forces are balanced by fluid drag, no longer exists over all wavenumbers. Rather, this mode only exists when it is slower than solute diffusion-corresponding to a finite range of wavenumbers. The well-known equipartition result, quantifying the size of membrane undulations due to thermal perturbations, is consequently limited in its validity to the aforementioned range. Moreover, this range shrinks as the membrane surface tension is increased, and above a critical tension, the membrane mode vanishes. Our findings are relevant when interpreting experimental measurements of membrane fluctuations, especially in vesicles at moderate to high tensions.

Solar interface evaporation is a sustainable and clean water production approach. Polymer hydrogels, as some of the core materials of solar-driven interface evaporation systems, have received extensive attention. However, traditional hydrogel foams have randomly distributed open cells and closed cells, which make it difficult to simultaneously achieve rapid water transport and efficient steam escape, and show excellent thermal insulation performance. In this study, a polyvinyl alcohol/acetylene black hydrogel foam (PAPHF) evaporator with a gradient pore structure was developed through a simple and scalable "foaming-resting-crosslinking-freezing" strategy. The top layer of this evaporator has a large-sized open-cell structure, which enhances light absorption, water transport and steam escape, while the bottom layer of the evaporator has a small-sized closed-cell structure, which can effectively reduce heat conduction loss and improve surface heat localization ability. The optimized PAPHF evaporator achieved an evaporation rate of 3.13 kg m^-2 h^-1 and an energy conversion efficiency of 88.9% under 1 sun radiation (1 kW m^-2), exceeding the performance of many of the reported evaporators of the same type. In addition, the PAPHF evaporator can effectively perform seawater desalination and wastewater purification. This study provides a new idea for the structural design of high-performance solar evaporators.

Correction for 'Capillary assembly of metal-coated polymer microspheres for interconnection in electronic applications' by Van Long Huynh et al., Soft Matter, 2025, 21, 6641-6648. DOI: https://doi.org/10.1039/D5SM00446B.

Dry granular intrusion and extraction occur commonly for off-road vehicles, foundation work, and plant uprooting. Although many models exist to describe such scenarios, reduced-order models such as granular resistive force theory (RFT), offer a good balance between accuracy and computational cost. RFT efficiently approximates the resistive force experienced by an intruder moving through a granular medium as a function of the intruder's velocity direction, geometry, and material parameters. However, due to the explicitly velocity-dependent nature of its formulation, it fails at modeling static conditions, the force build-up that occurs before flow, and stagnant points on moving intruders. We propose elastic RFT to remedy these shortcomings. Elastic RFT intrinsically models both granular elasticity and flow adjacent to intruders by splitting intruder motion into separate parts corresponding to elastic and plastic granular deformation. This allows force to build up elastically before flow and lets the plastic part of motion maintain RFT flow rules. We present the details of the underlying kinematic and constitutive assumptions for elastic RFT. Moreover, we also propose a procedure to couple RFT or elastic RFT to deformable intruders, which we demonstrate in applications of elastic RFT to sample plant uprooting problems treating the roots as nonlinear inextensible beams. We highlight potential application areas for elastic RFT coupled to deformable objects, including simulation of deformable wheel locomotion.

Hydrophobic aggregation is often described in terms of effective attractive forces between apolar units. In aqueous and soft-matter environments, however, aggregation necessarily involves a collective reorganization of the solvent, whose connectivity and confinement properties may play a central role. Here we investigate a deliberately minimal lattice model in which hydrophobic (apolar) segments interact with the solvent only through a local restriction rule, without introducing explicit solute-solute attractions. Each lattice site is occupied either by solvent or by an apolar segment at a fixed composition. Solvent sites are classified as restricted when the local density of nearby apolar segments exceeds a prescribed threshold, and configurations are sampled with a Boltzmann-like weight that penalizes the total number of restricted-solvent sites. Within this framework, aggregation can only arise through the reorganization of solvent restriction fields. By decomposing the solvent into free and restricted subsets, we analyze their connectivity using standard percolation diagnostics alongside conventional measures of solute clustering. Baseline simulations reveal that while amphiphile aggregation evolves smoothly with concentration, the restricted-solvent subset can undergo a sharp, kernel-dependent connectivity crossover: for sufficiently isotropic interaction neighborhoods, restricted water becomes a system - spanning only over an intermediate range of solute fractions. Free solvent, by contrast, remains spanning across the explored parameter range. Notably, these solvent-topology signatures are significantly sharper and more structured than the corresponding solute-ordering metrics. A systematic extension to larger system sizes refines this picture. The onset of restricted-solvent spanning remains localized and kernel selective, while high-density behavior becomes smoother and more fluctuation dominated, consistent with finite-size effects. Importantly, the amount of restricted solvent grows monotonically and robustly with system size, whereas its global connectivity reorganizes nontrivially. Taken together, these results support a restrained interpretation of hydrophobic aggregation as a solvent-driven topological crossover rather than a sharp thermodynamic phase transition, highlighting solvent topology as a sensitive diagnostic even when solute ordering remains gradual.

The mechanical and rheological properties of jammed packings of frictionless particles under shear strain remain not fully understood, even when the strain amplitude is very small and well below the yielding threshold. Systems above the jamming transition point φ_J are known to display two anomalous mechanical behaviors with respect to the driving frequency ω (or time t) and the strain amplitude γ. In the linear-response regime (γ → 0), the complex modulus exhibits an algebraic scaling, G(ω) ∼ ω^1/2 (or G(t) ∼ t^-1/2 in the time representation). In contrast, in the quasi-static limit (ω → 0), the modulus shows the nonlinear behavior, G(γ) ∼ γ^-1/2, a phenomenon referred to as softening. The ranges of ω and γ over which these algebraic scalings hold broaden as φ_J is approached from above, whereas both G(ω) and G(γ) vanish for φ < φ_J. In this study, we investigate the mechanical response in the regime where these two anomalies coexist in the vicinity of φ_J. To this end, we perform numerical analyses using two rheological protocols: oscillatory shear and transient stress relaxation. Our results demonstrate that the mechanical responses are not simply described as a superposition of the two algebraic relaxations and instead exhibit rich nonlinear viscoelastic behavior both above and even below φ_J.

Biomolecular condensates represent a frontier in cellular organization, existing as dynamic macromolecular structures driven out of equilibrium by active cellular processes. Here we explore active mechanisms of condensate regulation by examining the interplay between DEAD-box helicase activity and RNA base-pairing interactions within a reconstituted ribonucleoprotein condensate. We demonstrate that the ATP-dependent activity of a DEAD-box helicase-a key class of enzymes in condensate regulation-acts as a nonequilibrium driver of condensate properties through the continuous remodeling of RNA interactions. By combining the LAF-1 DEAD-box helicase with a designer RNA hairpin concatemer, we unveil a complex landscape of dynamic behaviors, including time-dependent alterations in RNA partitioning, evolving condensate morphologies, and shifting condensate dynamics. Importantly, we reveal an antagonistic relationship between RNA secondary structure and helicase activity which enables an initially homogeneous nonequilibrium state. By elucidating these nonequilibrium mechanisms, we gain a deeper understanding of cellular organization and expand the potential for active synthetic condensate systems.

Cell migration plays a central role in various biological processes, including development, wound healing, and cancer metastasis, and represents a fundamental form of self-organized motion at the cellular scale. These self-propelled cells can serve as microscale agents with potential applications in bioengineering and microsystem design. To realize such possibilities, it is essential to establish effective methods for controlling their migration. Conventional approaches, such as chemotactic, optogenetic, and substrate-based guidance, depend on external interventions that influence only a limited number of cells. Here, we present a proof-of-concept in Dictyostelium discoideum to bias cell migration by inducing deformation from within the cell. We demonstrate that glass microrods are internalized and that these internalized rods elongate the cells along their own axis. The elongated cells tend to migrate in the direction of their long axis, resulting in enhanced directional persistence. Unlike conventional methods requiring external deterministic cues or patterned environments, our approach enables cells to autonomously and persistently alter their migration behavior through internal morphological deformation. This study introduces a new framework for modulating cell migration and establishes a foundation for developing biohybrid systems that utilize living cells as self-propelled carriers.