Soft Matter最新文献

Correction for 'Phase-field model for quantitative analysis of droplet wetting' by Jeff Z. Y. Chen, Soft Matter, 2025, 21, 6937-6952, https://doi.org/10.1039/d5sm00593k.

The motility of microorganisms and small aquatic organisms provides a natural framework for studying active matter and its response to environmental perturbations. In this work, we experimentally investigate the trajectories of Paramecium caudatum and Artemia salina individuals under controlled laboratory conditions. Using video microscopy, we track the motion of organisms at low population densities and reconstruct individual trajectories over time. In addition to baseline conditions, we analyze stressed environments in which Paramecium caudatum are exposed to a toxic agent and Artemia salina are placed in distilled water. To characterize the statistical properties of the motion, we compute several trajectory-based metrics, including the mean square displacement, velocity and displacement distributions, average velocities, persistence times and lengths, tortuosity, and radius of gyration. These observables allow us to quantify changes in motility patterns across species, densities, and environmental conditions. To further interpret the observed dynamics, we develop coarse-grained stochastic models with parameters extracted directly from the experimental data. While P. caudatum is described within a run-and-tumble framework, including reversal events under stress, A. salina requires a run-and-tumble-like description with persistent orientational noise, accounting for the continuous directional fluctuations observed during its runs. The models reproduce the main trajectory-level observables used for quantitative comparison, namely tortuosity and radius of gyration. This combined experimental and modeling approach provides insight into how environmental stress modifies locomotion statistics. Our results highlight systematic differences in the statistical signatures of motion across conditions and organisms, suggesting that trajectory-based metrics may serve as indicators of physiological stress. Beyond their biological relevance, this work provides an accessible framework for active matter experiments in which individual-level statistics can be directly measured and modeled.

Adhesive contact measurements on soft polymers are commonly interpreted using Johnson-Kendall-Roberts (JKR) theory, which is formulated for circular contacts. Non-circular contacts generally require more complex elliptical-contact descriptions, making it unclear when a scalar measure of contact size is sufficient. Here, we examine contact formation and detachment in non-circular soft adhesive contacts using PDMS crossed-cylinder experiments. The cylinder crossing angle was varied from 30° to 90°, producing contacts ranging from highly elongated ellipses to nearly circular geometries while keeping the material pair fixed. During loading, the contact aspect ratio b/a initially evolved but rapidly approached an angle-dependent plateau, indicating approximately self-similar growth. This motivates, but does not by itself prove, an area-equivalent representation based on the radius together with the geometric-mean curvature radius . With these substitutions, the loading branches follow a JKR-type linearization and yield a nearly angle- and preload-independent loading work of adhesion, W_load = 24 ± 1 mJ m^-2. Comparable values obtained from Johnson-Greenwood elliptical-contact fits provide independent support that this result is not an artifact of neglecting ellipticity at the level of the global c(P) response. In contrast, unloading and pull-off are strongly history dependent. The unloading branches can still be represented by an effective JKR-like relation using c, but only with a substantially larger effective separation energy, W_unload,eff, which increases with preload and with decreasing crossing angle. A reduced viscoelastic model based on the same area-equivalent description rationalizes the delayed contact recession and the principal unloading response over 50°-80° at the tested displacement rate. These results show that contact formation in elliptical soft adhesive contacts is governed primarily by area-equivalent scaling, whereas detachment is governed by geometry- and history-dependent dissipative separation. The framework provides a practical route for analyzing non-circular soft contacts using simple global measures while retaining the essential distinction between contact formation and viscoelastic detachment.

The morphology of block copolymers (BCPs) is dictated by the relative volume fractions of the constituent blocks. Thus, in an equilibrated state, BCPs exhibit lamellar and non-lamellar structures, such as rods and spheres, for symmetric and asymmetric chain lengths, respectively. Transforming a cylinder-forming BCP with an inherent asymmetric composition into its equivalent asymmetric lamellar morphology is a challenging proposition, but could enable unique applications, such as harmonic frequency selective waveguides. Herein, we transform such an intrinsic PMMA cylinder forming PS-b-PMMA thin film system into its equivalent asymmetric lamellar structure, using the PMMA-philic ionic liquid (IL) EMIM-TFSI. We observed that the system formed nano-micelles consisting of a spherical PS core block and a PMMA/IL corona, upon casting films from a PMMA selective solvent, acetone. The IL migrates to the PMMA domains due to a combination of the preferential solvent and the high cohesive energy density (CED) of the IL promoting connectivity of the corona phase. Subsequent vacuum annealing of the films at elevated temperature (10 h at 180 °C) extracts the IL, lowering the CED barrier and allowing for progressive coalescence of the nano-micelles into continuous thin PS and PMMA layers, thus producing substrate parallel asymmetric PS-b-PMMA lamellae as confirmed by neutron reflectometry and surface island and hole formation phenomena. Stabilized by the substrate and air interfacial wetting interactions, these PS-b-PMMA lamellae with asymmetric composition in a deep meta-stable state, maintain their film structure with elevated temperature vacuum thermal annealing. This simple strategy has potential to be universally applied to dial-in alternate non-equilibrium morphologies for many pristine BCP systems, in defiance of thermodynamically controlled equilibrium morphologies, making them attractive for many nanotechnology applications, from membranes to photonic crystals.

Complex coacervate core micelles (C3Ms) assembled from cationic poly(D,L-lysine) (PRK, R is racemic) and poly(L-glutamate)-b-poly(ethylene glycol) (PLE-b-PEG) are investigated as preassembled, biomimetic nanoreactors for the mild synthesis of gold nanoparticles (AuNPs). Systematic comparison across coacervate architectures (AB + C, A + BC, AB + BC, and bulk A + C) demonstrates that the presence of a polymer-rich coacervate phase results in AuNP formation, with the PEG corona playing a dual role as both a microphase-separation driver and a steric stabilizer. Small-angle X-ray scattering (SAXS) experiments indicate that only architectures producing a well-defined dense coacervate core support AuNP formation, and that nanoreactor morphology is preserved during the early nucleation and growth periods. Time-resolved UV-visible light absorption spectroscopy, dynamic light scattering, and SAXS collectively allude to a kinetic framework consistent with the classical LaMer mechanism. These results establish polypeptide C3Ms as simple nanoreactors for mild metal/metal oxide nanoparticle synthesis.

We introduce naphthol-cholesteryl dimers showing that constitutional isomerism in a rigid core dictates mesophase structure and thermal stability. Planar naphthalene-diol cores linked to a chiral cholesteryl segment via flexible spacers permit subtle substitution changes that switch packing from V-shaped branches to linear rods, sharply altering the mesophase type and transition temperatures. Linear para-isomers promote tight π-π stacking, elevating average clearing temperatures (T_C) above 177 °C and broadening the nematic phase range. In contrast, V-shaped variants lower T_C to an average of 135 °C. XRD shows intercalated SmA layers, and UV-vis reveals concentration-dependent H-aggregation in the 2,6-series. Both dimers exhibit monomer/excimer fluorescence; 2,6-NCh-Dn shows enhanced solid-state emission and larger Stokes shifts-a difference that highlights aromatic geometry as a key template when designing mesogens.

Self-sustained oscillations of liquid-metal droplets represent a striking example of electrochemical-mechanical coupling in active matter. These liquid-metal droplets immersed in an aqueous solution oscillate toward and away from an electrode, in response to a continuous applied voltage. Recently, these oscillations have been studied in gallium-indium (GaIn) droplets. Though it is understood that the GaIn droplet self-oscillations are driven by surface tension variations, the details of the underlying mechanism remain incompletely understood, in part because previous investigations have relied primarily on optical observations. Here, we introduce an experimental platform that enables simultaneous electrochemical and optical characterization of self-oscillating GaIn droplets in an aqueous NaOH electrolyte under wet-electrochemical conditions in both an unconfined and laterally confined (Hele-Shaw) geometry. By correlating the time dependence of the current with the droplet dynamics, we could identify five distinct stages in the oscillation cycle, involving (i) droplet-electrode contact and positive charging, (ii) droplet spreading due to oxide growth, (iii) droplet detachment and asymmetrical contraction, (iv) inertial movement away from the electrode, and (v) electrowetting-driven return to the electrode. The measurements reveal two sequential driving mechanisms, namely asymmetrical contraction-induced inertial movement (following oxide dissolution) and an electrowetting-induced Marangoni flow associated with charge redistribution at the liquid-metal/electrolyte interface. Furthermore, we observe reversal of the interfacial flow direction and transient decoupling of surface and bulk motion. These findings provide new insight into the electrochemical-mechanical driving mechanism governing liquid-metal droplet oscillators in aqueous solutions.

In classic fracture mechanics, stress/strain concentration mediates the flow of energy toward the creation of new crack surfaces. However, the small scales and large deformations in this localized region make characterization challenging. Here, we visualize the deformation preceding a crack tip in an elastomeric material during fracture using the combination of reversible mechanophores and in situ cutting. Fluorescence intensity maps within tens of microns of the crack tip, which correlate to local deformation profiles, are made possible through Y-shaped cutting's ability to maintain fracture within the microscope's field of view. Comparison between these experimental intensity maps and deformation predictions from finite element analysis (FEA) highlight the importance of molecular probes in illustrating how continuum-level deformations translate to loads on molecular bonds in large deformation regions, such as those near the blade. FEA also highlights the presence of a previously unreported mechanophore deactivation zone within 2 µm of the blade tip.

We study a dilute system of non-motile chiral active particles confined in geometries ranging from straight channels to circular enclosures. Activity is introduced through chiral particle-wall interactions, modeled as tangential wall forces that generate the edge currents characteristic of chiral active matter. Remarkably, although the particles lack self-propulsion, these boundary currents induce density inhomogeneities in the presence of small but finite inertia. We show that boundary curvature drives a wall accumulation phenomenon: particles remain uniformly distributed in straight channels but accumulate near the boundaries of circular confinements. Numerical simulations and a hydrodynamic theory for the density and momentum fields quantitatively capture this curvature-induced wall-accumulation. These results identify boundary curvature as a fundamental control parameter for chiral edge transport and confinement-induced organization, with potential experimental relevance to spinning colloids and granular spinners.

Here, we present an open Python-based program with a graphical interface to characterise topological defects from two-dimensional time-lapses. This program computes the nematic orientation field, identifies defect positions, topological charges, and defect orientations, and estimates the splay-bend anisotropy parameter. The workflow is controlled by three detection parameters adjustable through the interface: the feature size, the order threshold and the phase contour radius. Validation on synthetic datasets with known ground truth yields less than 0.2% false positives and negatives and positional errors comparable to the resolution scale, and the absolute error of the splay-bend anisotropy is 0.03. In addition, we explain a correlation between the detected and input splay-bend anisotropy and provide a calibration curve. Next, we demonstrate applicability across biological systems spanning multiple scales. DeftPunk provides a versatile tool to characterise topological defects and infer elastic anisotropies from microscopy images, opening the way to systematic and quantitative investigations of active nematic dynamics in living systems.