Soft Matter最新文献

Drying of nanowire-laden elongated droplets is a ubiquitous process in printed electronics fabrication, where the resulting deposition pattern critically determines device performance by controlling nanowire alignment, connectivity, and percolating charge-transport pathways. However, the physical understanding of evaporation-driven deposition is still largely derived from studies of spherical droplets on homogeneous substrates. This gap limits the ability to predict and control deposit morphology in realistic printing scenarios. Here, we use mesoscale lattice Boltzmann simulations to investigate the drying of nanowire-laden elongated droplets on wettability-patterned substrates, focusing on the effects of droplet geometry, nanowire interactions, and nanowire length. The elongated droplet geometry is found to intrinsically induce distinct axial and transverse inhomogeneities in the final deposit. Increasing the effective attraction between nanowires, which mimics changes in surface chemistry or solvent conditions, can improve electrical connectivity but also promotes clustering and local ordering, reducing structural uniformity. In contrast, increasing nanowire length yields a dual benefit by improving long-range connectivity while simultaneously enhancing deposit homogeneity. Our findings provide design guidance for balancing electrical transport and structural uniformity in evaporation-driven printed electronics.

Gelation is the transition from a fluid state into a system-spanning, out of equilibrim soft-solid network through a hierarchical process that couples local particle interactions to mesoscopic clustering and global connectivity. In time-resolved small-angle X-ray scattering (SAXS), isosbestic points-scattering wavevectors where scattering intensity remains invariant-emerge during this transformation, yet their physical meaning has remained unclear. Here, we show that two isosbestic points, q₁ and q₂, observed during salt-induced gelation of Ludox colloids, reflect fundamental structural constraints rather than a two-species interconversion. The high-q point q₂ is a universal geometric marker, determined by particle contact distances, while the low-q point q₁ arises from Porod invariant conservation and separates rapidly arrested local clusters from the growing mesoscopic network. By decomposing the Porod invariant across the reciprocal-space regions defined by these points, we define a dimensionless parameter, Φ(t/t_g), whose sigmoidal evolution provides a simple, model-free, scale-resolved fingerprint of gelation. Together with the combined evolution of S(q_min, t) and S(q → 0, t), these results establish a quantitative model free framework linking local structuring, global connectivity, and scattering signatures, clarifying the role of isosbestic points in soft-matter transformations.

Brittle-ductile transition (BDT) is an important characteristic of amorphous (and semicrystalline) polymers. For a given strain rate, at temperatures above BDT, the polymers exhibit strain softening followed by yield and strain hardening, while at temperatures below BDT, the same materials exhibit brittle failure at relatively low strains. Surprisingly, today there is no simple model describing BDT as a function of polymer chemistry, sample history, deformation type, and strain rate. Experimental data suggest that BDT is often, though not always, associated with the β-transition. We formulate a simple scalar model to describe the visco-elasto-plastic shear stress-strain curves as functions of temperature and strain rate. We also show that within this model, there is always an upper bound on the strain rate where the material can have a uniform viscoplastic flow; this upper bound is assumed to represent the BDT for a given temperature. We stipulate that this upper bound is inversely proportional to the Johari-Goldstein β-relaxation time. Using our "general" Sanchez-Lacombe "two-state, two-(time)scale" (SL-TS2) model, we estimate the BDT for three polymers (polystyrene, poly(methylmethacrylate), and poly(vinylchloride)) and find a good agreement with experimental data.

The thermal gelation of yolk-granules, a protein-fat hybrid assembly found in egg yolk, is investigated employing X-ray photon correlation spectroscopy (XPCS). Time-resolved dynamics reveal five regimes during heat-induced gelation: regime-A, temperature-driven fast granule motion; regime-B, protein denaturation and aggregation; regime-C, protein gelation; and post-gelation regime-D and regime-E, marked by decreasing and increasing relaxation times, respectively. Compared with whole egg yolk, yolk-granules exhibit distinct microscopic dynamics and aging. At room temperature, yolk-granules show purely diffusive motion, whereas whole egg yolk displays hyper-diffusive behavior. During aging, whole egg yolk follows power-law relaxation, while yolk-granules exhibit non-monotonic relaxation through regimes D and E. The sol-gel transition time follows Arrhenius behavior with an apparent activation energy of 660 ± 10 kJ mol^-1, substantially higher than whole egg yolk (450 ± 20 kJ mol^-1). The D-to-E crossover also follows Arrhenius behavior, with an apparent activation energy of 325 ± 40 kJ mol^-1, illustrating an activation energy-driven process after the gel formation.

Predicting the time evolution of geometries formed during multiphase liquid-liquid phase separation is a challenge for statistical physics, intracellular organization and materials design. While the mechanisms underlying individual droplet structures have been intensively investigated, mechanistic analyses of larger-scale mesoscopic patterning remain limited. In this study, we use a DNA nanoparticle platform with tunable interparticle attractions to create a quasi-two-dimensional network of chains of DNA droplets, with each chain composed of two alternating, immiscible droplet phases. The network coarsens with time, with both the mesh size and the average droplet radius exhibiting a power-law growth that is independent of droplet adhesion strength and particle binding energy. Coarsening is driven by droplet collision-coalescence processes that only occur in the vicinity of network junctions. We show that the measured growth exponents can be understood based on the self-similar growth of both the droplet size distribution and the network geometry. Our results describe a new class of pattern formation dynamics in multicomponent phase-separating systems and suggest a means to control mesoscopic droplet organization.

Belousov-Zhabotinsky (BZ) gels exhibit autonomous and periodic deformation driven by the BZ reaction, enabling sustained deformation dynamics without dependence on externally imposed on-off control. To utilize BZ gels as autonomous soft actuators, it is essential to design structures that convert the propagation of chemical waves generated by the BZ reaction into macroscopically observable mechanical deformations. To convert the spatiotemporal propagation of chemical waves into macroscopically observable sequential mechanical deformation, we fabricated a single continuous BZ gel structure containing millimeter-scale free-standing pillar arrays using a BZ-gel formulation previously shown to form a microphase-separated structure with an amplified swelling-deswelling response. Furthermore, by contacting the gel with a silver (Ag) wire, we introduced a local reaction-field perturbation that likely promoted preferential chemical-wave propagation while maintaining sustained redox oscillations in the BZ gel. A representative pillar exhibited a tip displacement of approximately 0.30 mm, and the chemical-wave peak propagated along the pillar array at approximately 1.7 mm min^-1. In the pillar array, direct tip tracking showed delayed x-displacement peaks along the wave-propagation direction and nearly synchronous motion of pillars positioned in parallel. Thus, chemical-wave propagation was read out as sequential deformation of multiple pillars within a single continuous gel. Moreover, the proposed approach provides design guidelines for converting spatiotemporal patterns generated by chemical reactions into directional actuation, contributing to the development of soft robotics and biomimetic devices based on self-oscillating gels.

The COVID-19 pandemic has so far been sustained by recurrent outbreaks, largely owing to the strong contagiousness of SARS-CoV-2 (SARS2). Here, to explain its high infectivity from a mechanical viewpoint, we propose a multiscale mechanical model that links molecular-scale binding with cell-scale endocytosis in the initial stage of viral entry mediated by flexible spike (S) proteins. With three hinges in the stalk domain, SARS2-S has unanticipated orientational freedom, giving rise to a high binding affinity up to 10 times that of SARS-S binding with ACE2. Interestingly, when SARS2-S is in the "RBD-down" conformation, the affinity decreases dramatically to only one thousandth of that of SARS-S binding with ACE2, suggesting that the conformational hiding of the receptor-binding site in this flexible state could reduce its exposure to the host immune system and therapeutic antibodies. Therefore, the mechanical properties of S proteins can be exploited by the virus to enhance its recognition of host ACE2 and attachment to host cells. As S proteins bind to ACE2 receptors, the resulting S-ACE2 complexes bridge the viral and host-cell membranes and progressively accumulate at the virus-cell interface, while their deformation and loading states evolve continuously during subsequent membrane wrapping. Increasing molecular stiffness enhances the interfacial pulling force, and the resulting increase in complex stiffness further amplifies this effect. It should be noted that excessively high molecular or complex stiffness, a higher membrane bending modulus, and a larger viral size all increase the mechanical resistance to late-stage membrane wrapping. Together, these results shed light on the pivotal role of molecular flexibility in the initial stage of viral entry, showing how spike flexibility regulates both ACE2 recognition and the mechanical progression of membrane wrapping, and may provide guidance for vaccine development and drug design.

We compare seven elastic models for polymer networks in the context of phase separation within a gel, including a new model that combines the finite extensible Arruda-Boyce model and the slip tube model for entangled chains. We study incompressible uniaxial stretch and compression, and three volume-changing constrained-dimension deformations, in which the material can only deform in the designated dimension(s), while the constrained direction(s) remain(s) the same. Each model responds differently to large deformations, and our proposed model successfully describes both strain softening and strain hardening, which are both present in well-entangled elastomers. When considering phase separation, we show that the commonly used neo-Hookean model fails to admit a common tangent construction for phase coexistence for 3D deformations. This can be resolved by using a model with finite extension, such as the Arruda-Boyce model. In constrained-dimension deformations, where the gel's volume is allowed to change, for elastic models in which phase coexistence is possible, the critical temperature increases and the critical concentration decreases with increasing deformation dimensions. This strong dependence of the phase diagram on spatial dimension and geometry distinguishes phase separation in elastic media from conventional liquid-liquid phase separation.

By strategically integrating resilin-like polypeptides (RLPs) with computationally designed coiled coils computationally designed, the distinct advantages of each component were effectively utilized: the pre-organized structure of the coiled coils provides a rigid, anisotropic core to present the RLP chains, while RLP-mediated association can trigger hierarchical organization and the emergence of ordered nanostructures. To understand the fundamental driving forces affecting self-assembled nanostructures, peptide-based hybrids, RLP-coiled-coil bundles, were simulated across various temperatures with varied guest residues in the RLP chains. The simulations, spanning temperatures from 293 K to 403 K, revealed a pronounced solution temperature for association, with aromatic variants (tryptophan and phenylalanine) exhibiting stronger aggregation and higher transition temperatures than their aliphatic (leucine and valine) counterparts. Detailed cluster analyses, chain conformation assessments, and residue-residue interaction mappings highlighted the critical role of aromatic residues in driving the formation of ordered one-dimensional fibrillar structures, whereas non-aromatic variants tended to form more random aggregates. Complementary experimental cryo-TEM supported these findings by showing long, twisted nanofibers for tryptophan constructs and discrete, smaller peptide structures for valine-containing systems. The results provide valuable insights into the molecular interactions underpinning self-assembly, paving the way for the rational design of bio-inspired materials with tunable nanostructures.

Nanomedicine platforms are increasingly utilized in biomedical applications as direct therapeutics, delivery vehicles, and hydrogel nanocomposites. As many of these applications occur in dynamic biological environments, understanding how nanomaterials influence soft material sliding behavior is critical for their successful implementation. While nanoparticle composition and surface chemistry have been shown to affect frictional behavior in some systems, the influence of nanoparticle capping ligand chemistry under different modes of therapeutic use remains understudied. To compare these effects, gold nanoparticles (Au NPs) capped with citrate, cetyltrimethylammonium bromide, polyvinylpyrrolidone (PVP), and poly(acrylic acid) (PAA) were examined both as solution additives, representing direct nanomedicine injection, and as additives forming polyacrylamide (PAM) hydrogel nanocomposites. Friction measurements were conducted using a rheometer with a tribology adapter to quantify sliding behavior over time. As solution additives, Au NP capping ligand chemistry produced minimal differences in hydrogel frictional behavior. In contrast, incorporation of polymer-based ligands (PVP and PAA-capped Au NPs) into PAM hydrogel nanocomposites produced pronounced time-dependent frictional responses, with increasing friction during sliding. Comparison with pH-dependent sliding indicates that this friction evolution cannot be fully explained by hydrolysis-driven mechanisms. Instead, the results suggest that polymeric NP ligands introduce charge-mediated interfacial effects that emerge during sliding. These findings demonstrate that NP incorporation can alter the physicochemical mechanisms governing soft-material friction, highlighting the importance of interfacial chemistry in dynamic hydrogel systems.