Liquid rise into a capillary has been long studied. Capillary force is usually balanced with the inertia or viscous force for its dynamics during the initial rising stage. However, long-time scale rise of the liquid front is missing up to now. In our observation, the liquid front keeps rising for hours and even longer after the fast rise. Alkane liquids are used to study this long-time scale liquid rise. We observe a strong deviation from Lucas-Washburn prediction at the longtime scale. A model based on the Kramer theory is developed to consider the non-equilibrium thermal motions of liquid molecular when the system is near its equilibrium. Comparing model predictions and experimental observation, we propose a thermally activated rising process in the final stage of liquid imbibition. This will open new ways of developing new protocols to extract oils and shale gases.

Spreading of pure simple liquid dates back to century ago and its understanding is very well documented. For example, the spreading of retraction of liquid droplets can be described by power laws. One of the best known is the Cox-Voinov law. This law describes perfectly the behavior of PEG-ran-PPG monobutyle ether liquid, PEG. Besides, rheology of the complex fluids, hereby suspensions of PEG mixed with polystyrene beads, can also be well predicted by the Eilers empirical correlation. However, if the viscosity of the suspension solution is directly injected into the Cox-Voinov equation, a conspicuous deviation is observed from experiments. An imaging system to simultaneously monitor the side-view spreading and the top-view morphology of bead distribution is constructed. We find a depletion zone of particles in the liquid front zone, the size of which depends strongly on the bead size, which is a direct indication of the confinement effect. Based on those observations, we propose a depletion zone in the wetting front that decreases the overall viscous dissipation. We adapt the Cox-Voinov solution by proposing a simple geometrical matching condition and find it captures the orders and the trends of effective viscosity as a function of the bead size.

We studied the dependence of solid deposit shape obtained by free drying of sessile drops on the particles concentration and Derjaguin–Landau–Verwey–Overbeek (DLVO) particle/substrate interaction. In contrast to previous contributions using pH as a control parameter of interactions, we investigated an unprecedentedly wide range of concentrations and particle/substrate DLVO forces by modifying the nature of the substrate and particles as well as their size and surface chemistry whereas long-distance repulsive interactions between particles were maintained for most of the drying time. Our main result is that the different shapes of deposits obtained by modifying the particle concentration are the same in the different regimes of concentration regardless of particle/substrate interaction in the studied range of DLVO forces and particle concentrations. The second result is that, contrary to expectations, the dominant morphology of dry patterns at low particle concentration always shows a dot-like pattern for all the studied systems.

Gel layers bound to a rigid substrate are used in cell culture to control differentiation and migration and to lower the friction and tailor the wetting of solids. Their thickness, often considered a negligible parameter, affects cell mechanosensing or the shape of sessile droplets. Here, we show that the adjustment of coating thickness provides control over energy dissipation during the spreading of flowing matter on a gel layer. We combine experiments and theory to provide an analytical description of both the statics and the dynamics of the contact line between the gel, the liquid, and the surrounding atmosphere. We extract from this analysis a hitherto-unknown scaling law that predicts the dynamic contact angle between the three phases as a function of the properties of the coating and the velocity of the contact line. Finally, we show that droplets moving on vertical substrates coated with gel layers having linear thickness gradients drift toward regions of higher energy dissipation. Thus, thickness control opens the opportunity to design a priori the path followed by large droplets moving on gel-coated substrates. Our study shows that thickness is another parameter, besides surface energy and substrate mechanics, to tune the dynamics of liquid spreading and wetting on a compliant coating, with potential applications in dew collection and free-surface flow control.

Elastocapillarity describes the deformations of soft materials by surface tensions. Although the vast majority of elastocapillarity experiments are performed on soft gels, because of their tunable mechanical properties, the theoretical interpretation of these data has been so far undertaken solely within the framework of linear elasticity, neglecting the porous nature of gels. We investigate in this work the deformation of a thick poroelastic layer with surface tension subjected to an arbitrary distribution of time-dependent axisymmetric surface forces. Following the derivation of a general analytical solution, we then focus on the specific problem of a liquid drop sitting on a soft poroelastic substrate. We investigate how the deformation and the solvent concentration field evolve in time for various droplet sizes. In particular, we show that the ridge height beneath the triple line grows logarithmically in time as the liquid migrates toward the ridge. We then study the relaxation of the ridge following the removal of the drop and show that the drop leaves long-lived footprints after removal that may affect surface and wetting properties of gel layers but also the motion of living cells on soft materials.

When a liquid propagates on a solid surface, it displaces the surrounding air. However, when the liquid moves fastenough, air will be entrained as small bubbles into the liquid phase, thus introducing the instability of the contact line. A saw-tooth shape of the contact line can be observed in this case. When we drop a smooth hydrophilic sphere into a water tank, a thin liquid film is splashed around the periphery of the sphere and it climbs up to the sphere pole. If the moving velocity of this thin liquid film is high enough, air will be introduced between the sphere wall and the splashed liquid, thus resulting into a big cavity when the sphere is totally immersed into the liquid tank. Meanwhile, if the surface of the sphere is polished with sandpaper, this critical velocity can be dramatically decreased. Higher roughness makes the entrainment velocity lower. From the confocal microscopy, we propose an instant creation of air pocket when the liquid front moves across the roughened surface. The calculation of the interfacial capillary energy based on the surface topology successfully explains the decrease of the wetting failure velocity. This reveals a novel concept that dynamic wetting on hydrophilic rough surfaces can be similar to that on hydrophobic surfaces and brings a new way to design surfaces with specific wetting properties.