Soft Matter最新文献

Local variations in surface tension can induce complex fracture dynamics in thin interfacial films. Here, we investigate the fracture patterns that emerge when a localized surface-tension perturbation is applied to a sumi film supported on a water-glycerol subphase. Sumi is a traditional Japanese carbon black ink, and this process, referred to as sumi-wari, produces aesthetically pleasing, star-shaped crack patterns with multiple spikes radiating from the perturbation site. The number of crack spikes increases with the viscosity of the subphase, controlled here by the addition of glycerol. Atomic force microscopy measurements reveal that the effective stiffness of the sumi film decreases as glycerol concentration increases. This suggests a strong coupling between the subphase properties and the mechanics of the sumi film. To capture the dynamics of sumi-wari, a phenomenological model is outlined, based on an overdamped equation of motion for particles connected by breakable springs. Numerical simulations reproduce both the morphology and the experimental trends of sumi-wari: the number of cracks and their temporal evolution depend on the spring stiffness, mirroring the behavior observed for subphases with different viscosities. These findings demonstrate how the interplay between surface-tension gradients, subphase properties, and film mechanics governs local fracture and pattern formation in fluid-supported thin films.

Two mechanisms for film deposition during the electrolyte dipping process are examined. The conventional, widely accepted, mechanism proposes that electrolyte on a former, immersed in latex compound for a controlled dwell time, diffuses into the compound and a wet gel coagulates on the former where the electrolyte concentration is above the critical coagulation value. An alternative mechanism proposes that deposition occurs via particle movement towards the former, driven by diffusiophoresis. The two mechanisms are examined using dipping nitrile latex compound and various mono and divalent cation electrolytes. The similarity of the total solids content (TSC) of the deposit on the former to that of the compound, the coagulated nature of the deposit and the success, at short dwell times, of a diffusion-coagulation model show that diffusion and coagulation operates exclusively for the divalent cations. For the monovalent cation electrolytes, this mechanism is also dominant, but the TSC of the deposits suggests that diffusiophoresis also plays a small part in the deposition process. A model for the two mechanisms acting together was devised and applied to deposition given by three monovalent electrolytes. This gave deposit TSCs that agreed with the diffusiophoretic prediction and was independent of dwell time. Quantitatively, the calculated amounts of deposit agreed reasonably well with experiment. The model therefore provides some support for diffusiophoresis affecting deposition for monovalent electrolytes. The reason(s) for the different diffusiophoresis behaviour of the monovalent and divalent electrolytes is suggested to be due to the much lower critical coagulation concentration for the divalent cations.

We present an experimental method to fabricate centimetric thin elastic capsules with a highly uniform thickness and negligible bending stiffness using silicone elastomers. In our experiments, the capsule thickness is tunable at fabrication, while internal pressure and hoop (circumferential) stress are adjustable via hydrostatic inflation once the capsules are filled and immersed in water. Capsule mechanics are probed through hydro-elastic waves generated by weak mechanical perturbations at the capsule interface. By analyzing the surface wave dynamics in the Fourier domain, we extract the in-plane stress and demonstrate that the hydro-elastic waves are exclusively governed by hoop stress. This provides a controllable macroscopic analogue of liquid drops characterised by an effective surface tension, allowing the capsules to be modeled as large-scale "elasto-drops" with an inflation and thickness tunable effective surface tension. In this limit, bending stiffness is negligible over the experimentally relevant wavelengths, so that the shell dynamics are governed primarily by in-plane tension. Our work demonstrates that elasto-drops serve as a robust model system for parametric studies of large-scale analogues of liquid drops with experimentally adjustable surface tension.

Advances in 3D printing technology now enable the precise positioning of microscopic material voxels to form complex structures. Combined with emerging multi-material capabilities and printable responsive materials, this opens new possibilities for digital composite materials and 3D printing of shape-transforming structures, a process known as 4D printing. Building upon these advancements, we present a novel methodology for designing and fabricating digitized 4D-printed shape-transforming sheets. We 3D print responsive continuous sheets composed of two layers, each consisting of active and passive voxels meticulously positioned to form thin structures that transform on demand. Our approach addresses a long-standing challenge in the field: the independent and simultaneous programming of lateral geometry and intrinsic curvature. This unprecedented control over the resulting shape unlocks new opportunities in synthetic shape-morphing materials. We provide a general algorithmic approach that is material-agnostic and enables systematic design of shape transformations with potential capabilities for programmable mechanical properties and multi-actuation-mode systems and applications in soft robotics and deployable structures.

We report a simple and robust method for generating centimeter-sized lipid vesicles (ultra-giant lipid vesicles, UGLVs) by dripping an aqueous solution onto a thin lipid layer floating on the surface of an aqueous phase. A mixture of oleic acid and phospholipids was used to form an interfacial lipid layer. During dripping, the aqueous droplet initially remained above the lipid layer but gradually sank owing to gravity as its volume increased. Once the droplet volume reached several cubic centimeters, it detached from the air-liquid interface and spontaneously formed a stable vesicle with a diameter of several centimeters. Notably, the UGLV remained stable even under mechanical perturbation using a spatula. Furthermore, UGLVs encapsulating the Belousov-Zhabotinsky oscillatory reaction medium were successfully prepared. Neighboring UGLVs exhibit spontaneous synchronization of chemical waves upon contact, demonstrating that UGLVs can function as a unique type of smart chemical reactor.

Recently discovered ferroelectric nematic (N_F) liquid crystals are fluids with a polar orientational order. The electric polarization vector can be aligned by an electric field and by surface anchoring. Here, we explore how the polarization field and effective viscosity of the N_F materials are affected by shear flows. We explore three N_F materials, abbreviated RM734, DIO, and a room-temperature FNLC919, all of which exhibit a paraelectric nematic (N) and an N_F phase. All materials show an increase in the effective viscosity upon cooling, with Arrhenius behavior in broad temperature ranges except near the phase transitions. In DIO and FNLC919, the antiferroelectric SmZ_A phase separating the N and N_F phases shows a strong dependence of the effective viscosity on the shear rate: this viscosity is lower than the viscosity of the N and N_F phases at high shear rates ( = 500 s^-1) but is much higher when the shear rate is low,  = 2.5 s^-1. The behavior is associated with the layered structure of the SmZ_A phase. All mesophases in all three materials exhibit shear-thinning behavior at low shear rates (<100 s^-1) and a nearly Newtonian behavior at higher shear rates. In terms of alignment, we observe three regimes in the N and N_F phases: flow-alignment at low shear rates,  < 10² s^-1, a log-rolling regime with the director and polarization along the vorticity axis at  > 10³ s^-1, and polydomain structures at intermediate rates. In the flow-aligning regime, the N_F polarization does not tilt away from the shear direction, which is in sharp contrast to the flow-induced tilt of the N director. The effect is attributed to the avoidance of splay deformations and associated space charge in the flowing N_F. The temperature and shear rate dependencies of the viscosity and the uncovered shear-induced structural effects of N_F advance our understanding of these materials and potentially facilitate their applications.

Rubber-ice friction is governed by the coupled contributions of viscoelastic adhesion and interfacial heating. This work provides unique in situ/in operando insight into the friction mechanisms from the macroscopic to the molecular scale using combined experimental measurements and analytical modelling approaches. Simultaneous force and real contact area imaging were used to quantify the real shear stress of SBR-silica elastomers spanning a small-strain, low-frequency shear-modulus range of 1-8 MPa (a low glass transition temperature of ∼-60 °C) during pure sliding over 50 µm s^-1-1 m s^-1 and at environmental temperatures down to -30 °C. The normalized real contact area exhibited a non-monotonic velocity dependence; together with a bell-shaped shear stress-velocity curve, this revealed three friction regimes: at low velocity, adhesion and viscoelastic dissipation dominated thermal effects; near the peak, frictional heat generation increased; and at high velocity, thermally driven mechanisms, including advection-dominated heat removal, became more significant, with the possible occurrence of localized interfacial melting. No bulk melting was observed. The novelty of this work relies on bridging the scales in ice-rubber friction mechanisms. At the macroscopic scale, a simple thermal analysis of the rubber-ice sliding interface yielded a dimensionless average contact temperature that collapsed across all compounds and test conditions considered. At the molecular scale, Chernyak-Leonov kinetics was used to describe elastomer chain attachment-detachment on ice and its temperature dependence. Successfully confronting our experimental results with this multiscale model led to a predictive interfacial shear stress model that, when supplied with the measured real contact area, reproduced both the magnitude and shape of the friction response.

We describe combined experiments and simulations of single droplet breakup during flow-driven interactions with a circular obstacle in a quasi-two-dimensional microfluidic chamber. Due to a lack of in-plane confinement, the droplets can also slip past the obstacle without breaking. Droplets are more likely to break when they have a higher flow velocity, larger size (relative to the obstacle radius R), smaller surface tension, and for head-on collisions with the obstacle. We also observe that droplet-obstacle collisions are more likely to result in breakup when the height of the sample chamber is increased. We define a nondimensional breakup number Bk ∼ Ca that accounts for changes in the likelihood of droplet break up with variations in these parameters, where Ca is the Capillary number. As Bk increases, we find in both experiments and discrete element method (DEM) simulations of the deformable particle model that the behavior changes from droplets never breaking (Bk ≪ 1) to always breaking for Bk ≫ 1, with a rapid change in the probability of droplet breakup near Bk = 1. We also find that Bk ∼ S^4/3, where S characterizes the symmetry of the collision, which implies that the minimum symmetry required for breakup is controlled by a characteristic distance h ∼ R.

Coalescence of droplets on liquid-infused surfaces has been extensively investigated for isotropic lubricants, where interfacial and hydrodynamic responses are well described by geometry-based and mass-spring models. However, the corresponding dynamics on anisotropic lubricating films, such as liquid crystals (LCs), remain largely unexplored. In this work, we report the use of high-speed imaging to study the attraction and coalescence of millimetre-sized water droplets on two classes of substrates, covered with a thin LC overlayer: LC-infused textured surfaces (LCITS) and LC-infused porous surfaces (LCIPS). On both substrates, the droplets coalesce in three stages over approximately one minute: long-range capillary-mediated attraction, drainage of the lubricant within the wetting ridge, and final merging accompanied by in-plane oscillations of the formed droplet. On LCITS, the initial approach velocities and post-merging dynamics are broadly consistent with the geometry-based mass-spring model developed for oil-impregnated surfaces of a similar type. However, on LCIPS, where a thicker lubricating film produces a larger wetting ridge, we observe substantially reduced attraction and merging velocities, no oscillations were resolved within our temporal resolution at the first velocity peak, and drainage times strongly influenced by evaporation. In the final stage, the peak velocity mainly depends on the LC mesophase and is nearly independent of droplet size, while the oscillation period scales approximately with the square root of the droplet radius. These results clarify how the porous LC scaffold and enlarged wetting ridge alter droplet-droplet interactions and coalescence dynamics relative to textured silicone substrates.

Liquid-liquid phase separation (LLPS) in the pre-Ouzo region governs the early-stage aggregation of amphiphiles, dictating the non-equilibrium evolution of soft materials. However, classical turbidimetry, which defines phase boundaries by macroscopic cloudiness, is blind to this metastable regime. Here, we introduce an integrated fluorescence-microscopy ternary phase mapping approach that directly probes the pre-Ouzo region in a canonical ethanol-water-amphiphile system. This method reveals critical aggregation concentrations that are 2-3 orders of magnitude below the binodal-a regime inaccessible to turbidimetry. Applying this diagram to naturally aged Baijiu (1-20 years), a dynamically evolving colloidal system, uncovers a pronounced aging-enhanced solubilization: the dissolution ratios of key amphiphiles (hexanoic acid and ethyl hexanoate) exceed 96%, with dissolved concentrations far surpassing static equilibrium predictions. Mechanistic investigations show that this phenomenon arises from the synergistic restructuring of ethanol-water hydrogen-bond networks and the expansion of hydrophobic microdomains. Our work not only provides a high-resolution tool for mapping non-equilibrium phase behavior but also establishes a direct link between slow microstructural evolution and the emergence of kinetically stabilized, supersaturated states in complex fluids.