Wetting Transition Research Articles

Long-Term Resistance to Phase Change-Induced Wetting Transition on Biphilic Armored Superhydrophobic Surfaces.

Material surfaces maintaining a liquid super-repellent is crucial in fields such as anti-fouling, drag reduction, and heat transfer. Superhydrophobic surfaces provide an effective approach but suffer from phase change-induced wetting transitions, hindering their practical applications. In this work, Biphilic armored superhydrophobic surfaces (BASS) are designed by integrating hydrophilic interconnected surface frames with superhydrophobic nanostructures. The hydrophilic top of the frame provides spatial selectivity for condensate droplet nucleation, and superhydrophobic nanostructures enable staying dry. Further growth, coalescence, jumping, and roll-off of the condensate droplets on BASS, show remarkable resistance to phase change-induced wetting transition. It still maintains stable superhydrophobicity when exposed to 100°C of steam for 240 h, at least two orders of magnitude improvement over traditional superhydrophobic surfaces. Such a designing BASS provides an effective approach to address the phase change-induced wetting transition, thereby extending the practical application in the fields of condensation heat transfer, anti-fouling, and fluid transportation of superhydrophobic surfaces.

Macroinvertebrate, algal and diatom assemblages respond differently to both drying and wetting transitions in non‐perennial streams

Abstract Biological assemblages in streams are influenced by hydrological dynamics, particularly in non‐perennial systems. Although there has been increasing attention on how drying impacts stream organisms, few studies have investigated how specific characteristics of drying and subsequent wetting transitions influence biotic responses via resistance and resilience traits. Here, we characterized how hydrologic metrics, including those quantifying drying and wetting transitions as well as dry and wet phases, alter diversity and composition of three aquatic assemblages in non‐perennial streams in southern California: benthic macroinvertebrates, soft‐bodied algae and diatoms. We found that flow duration prior to sampling was correlated with variation in macroinvertebrate and soft‐bodied algal assemblage composition. The composition and richness of diatom assemblages, however, were predominantly influenced by the drying start date prior to sampling. Contrary to other studies, the duration of the dry phase prior to sampling did not influence the composition or richness of any assemblage. Although our study was conducted within a region in which each assemblage experienced comparable environmental conditions, we found no single hydrologic metric that influenced all assemblages in the same way. The hot‐summer Mediterranean climate of southern California likely acts as a strong environmental filter, with taxa in this region relying on resistance and resilience adaptations to survive and recolonize non‐perennial streams following wetting. The different responses of algal and diatom assemblages to hydrologic metrics suggest greater resilience to drying and wetting events, particularly for primary producers. As drying and wetting patterns continue to change, understanding biodiversity responses to hydrologic metrics could inform management actions that enhance the ecological resilience of communities in non‐perennial streams. In particular, the creation and enhancement of flow regimes in which natural timing and duration of dry and wet phases sustain refuges that support community persistence in a changing environment.

Quantum wetting transition in the cluster Ising model

The wetting transition in the one-dimensional cluster Ising model with opposite boundary fields is studied. Tuning one boundary field while fixing another leads to the occurrence of phase transitions, where the transition points depend on the cluster coupling. Furthermore, the phase diagram is divided into three regions with different phase transition. For weak and strong cluster coupling, the phase transition is continuous and belongs to the same universality of transverse Ising model with boundary fields. For intermediate cluster coupling, the phase transition is first order. In the strong cluster coupling region, the critical region becomes exponentially small and the asymptotic behavior is absent even for lattice size up to 104. A numerical method to solve the energy gap and the correlation length is proposed on an infinite long spin chain. With this method, one can get the critical behavior as close to the critical point as possible provided that the numerical accuracy is high enough. In the light of this method, we clearly show that there is a preasymptotic regime in which the apparent critical exponents depend on the cluster coupling. Moreover, we obtain the accurate energy gap exponent zν and the correlation length exponent ν in the asymptotic critical region.

Wetting State Transition of Laser Direct Writing Aluminum Surface Based on Coupling Effect of Micro/Nanoscale Characteristics.

Micro/nanostructured metal surfaces fabricated by laser direct writing (LDW) have been widely used in wettability-related fields. Previous studies focused on the effects of surface structural patterns or chemical composition on wettability, while the coupling mechanism and respective contributions of the two are not distinct. This paper reveals the coupling effect of micro/nanoscale characteristics on the wettability of LDW aluminum surfaces and elucidates the transition mechanism between wetting states on the surfaces with linear laser energy density. Through the contact angle experiments, a wetting state transition of the LDW surface is found from a more hydrophilic than pristine rose petal effect to lotus effect. Based on the bionic analysis method of the superhydrophobicity factors of lotus leaves, the contributions to the wettability of LDW surfaces are divided into the micro/nanoscale characteristics. The theoretical model for identifying the wetting state of a rough surface is proposed. Based on this model, the average Young's contact angle, θ̅Y, is calculated, which indicates the contribution of the nanoscale characteristics. During the transition process from rose petal effect to lotus effect, θ̅Y > 90° is a necessary condition for detachment from the rose petal effect, which is contributed by the high specific surface organic adsorption at the nanoscale. What is more, the wetting state determined by the microscale characteristics further enhances its hydrophobicity, leading to the lotus effect. Based on the wetting state identification model and the Cassie-Baxter equation, the change of micro/nanoscale characteristics on aluminum surfaces after LDW treatment is presented, and the influence of micro/nanoscale characteristics on the wetting state is decoupled and quantified. This research helps to coordinate the effects of surface structure and chemical composition on wettability in the design of specific wettability functional surfaces and can also be applied to other high heat density surface processing fields.

Polarity-Induced Reactive Wetting: Spreading and Retracting Sessile Water Drops.

Wetting is typically defined by the relative liquid to solid surface tension/energy, which are composed of polar and nonpolar subcontributions. Current studies often assume that they remain invariant, that is, surfaces are wetting-inert. Complex wetting scenarios, such as adaptive or reactive wetting processes, may involve time-dependent variations in interfacial energies. To maximize differences in energetic states, we employ low-energy perfluoroalkyls integrated with high-energy silica-based polar moieties grown on low-energy polydimethylsiloxane. To this end, we tune the hydrophilic-like wettability on these perfluoroalkyl-silica-polydimethylsiloxane surfaces. Drop contact behaviors range from invariantly hydrophobic at ca. 110° to rapidly spreading at ca. 0° within 5 s. Unintuitively, these vapor-grown surfaces transit toward greater hydrophilicity with increasing perfluoroalkyl deposition. Notably, this occurs as sequential silica-and-perfluoroalkyl deposition also leaves behind embedded polar moieties. We highlight how surfaces having such chemical heterogeneity are inherently wetting-reactive. By creating an abrupt wetting transition composed of reactive and inert domains, we introduce spatial dependency. Drops contacting the transition spread before retracting, occurring over the time scale of a few seconds. This phenomenon contradicts current understanding, exhibiting a uniquely (1) decreasing advancing contact angle and (2) increasing receding contact angle. To explain the behavior, we model such time- and space- dependent reactive wetting using first order kinetics. In doing so, we explore how reactive and recovery mechanisms govern the characteristic time scales of spreading and retracting sessile drops.

Collective wetting transitions of submerged gas‐entrapping microtextured surfaces

AbstractNumerous natural and industrial processes entail the spontaneous entrapment of gas/air as rough/patterned surfaces are submerged under water. As the wetting transitions ensue, the gas diffuses into the water leading to the fully water‐filled state. However, the standard models for wetting do not account for the microtexture's topography on collective wetting transitions. In other words, it is not clear whether the lifetime of n cavities arranged in a one‐dimensional (I‐D) line or a two‐dimensional (II‐D) (circular or square) lattice would be the same or not as a single 0‐D cavity. In response, we tracked the time‐dependent fates of gas pockets trapped in I‐D and II‐D lattices and compared them with wetting transitions in commensurate 0‐D cavities. Interestingly, the collective wetting transitions in the I‐D and the II‐D arrays had a directionality such that the gas from the outermost cavities was lost the first, while the innermost got filled by water the last. In essence, microtexture's spatial organization afforded shielding to the loss of the gas from the innermost cavities, which we probed as a function of the microtexture's pitch, surface density, dimensionality, and hydrostatic pressure. These findings advance our knowledge of wetting transitions in microtextures and inspiring surface textures to protect electronic devices against liquid ingression.

Influence of chemistry and topography on the wettability of copper

To understand the complex interplay of topography and surface chemistry in wetting, fundamental studies investigating both parameters are needed. Due to the sensitivity of wetting to miniscule changes in one of the parameters it is imperative to precisely control the experimental approach. A profound understanding of their influence on wetting facilitates a tailored design of surfaces with unique functionality.We present a multi-step study: The influence of surface chemistry is analyzed by determining the adsorption of volatile carbonous species (A) and by sputter deposition of metallic copper and copper oxides on flat copper substrates (B). A precise surface topography is created by laser processing. Isotropic topography is created by ps laser processing (C), and hierarchical anisotropic line patterns are produced by direct laser interference patterning (DLIP) with different pulse durations (D).Our results reveal that the long-term wetting response of polished copper surfaces stabilizes with time despite ongoing accumulation of hydrocarbons and is dominated by this adsorption layer over the oxide state of the substrate (Cu, CuO, Cu2O). The surfaces’ wetting response can be precisely tuned by tailoring the topography via laser processing. The sub-pattern morphology of primary line-like patterns showed great impact on the static contact angle, wetting anisotropy, and water adhesion. An increased roughness inside the pattern valleys combined with a minor roughness on pattern peaks favors air-inclusions, isotropic hydrophobicity, and low water adhesion. Increasing depth of the primary topography can also induce air-inclusions despite increasing peak roughness while time dependent wetting transitions were observed.

Moving contact line dynamics for capillary-driven microfluidics in wetting transition regime

The dynamics of moving contact lines (MCLs) dominate the behavior of capillary-driven microfluidics, which underlie many applications including microfluidic chips. The capillary displacement dynamics in the quasi-static regime has been extensively studied. However, the behavior of MCLs in the dynamic wetting transition regime remains largely unexplored, and previously established MCL dynamic models may be inadequate. In this study, a novel capillary displacement experiment is introduced, which is achieved by reversely introducing microfluidics with surface tension differences, where the one with low surface tension undergoes the wetting transition. In addition, a generalized Navier boundary condition (GNBC)-based model of capillary displacement dynamics is developed within the framework of diffusive interface theory to investigate the MCL dynamics in the wetting transition regime. The oscillation-relaxation process is experienced for phase interface and microscopic dynamic contact angle θd in the wetting transition regime. Spontaneous filling distance follows dfill*∼t1/2, and reaching quasi-static stage follows dfill*∼t1. The previously neglected mechanism of inertial-viscous competition dominates the early dynamics of such dynamic wetting transition processes. θd∝ucl is observed to be valid solely under conditions where viscosity dominates, but it breaks down in the presence of dominant inertial effects. An escalation in slip substantially diminishes the influence of inertia, with frictional dissipation mediated by slip emerging as the predominant factor in the capillary-driven early dynamics. The origin of uncompensated Young's stress in the GNBC and its correlation with capillary forces is unified, unveiling the underlying physical mechanism governing the dynamics at the MCL. Finally, by decoupling the analysis of viscosity and slip, a new θd-viscous-slip formulation is proposed, in agreement with the model predictions.

Wetting of nanoscale water films on hierarchically structured surfaces

Surfaces with hierarchical structures significantly enhance the hydrophobic properties of solids, proving crucial for diverse applications including self-cleaning, anti-icing, and contamination prevention. In this study, we directly observe the dynamic wetting transitions of nanoscale water films on desirable textured surfaces decorated with dual-scale roughness between various wetting states encompassing Cassie–Cassie, Wenzel–Cassie, Cassie–Wenzel, and Wenzel–Wenzel states. Additionally, detailed information on the wetting of the water film on desirable textured surfaces decorated with dual-scale roughness is obtained using atomistic simulations in conjunction with sampling techniques. Through observation of the dynamic wetting transition, two common types of wetting pathways are directly captured, dubbed the preferential primary intrusion and secondary intrusions. The wetting follows which pathway is dependent on Hs/Ss of the small-scale roughness. The mechanisms behind the wetting transitions are revealed based on corresponding free-energy pathways. Moreover, the effect of aspect ratio and intrinsic contact angle on the wetting behavior has been studied. Subsequently, we construct a wetting phase diagram to exhibit all the possible outcomes and identify different wetting regimes. This work paves the way to understanding the wetting mechanisms on nanoscale textured surfaces with two-tier roughness, which can help to design a hydrophobic surface with superior robustness.

Dynamical wetting transition of a stretched liquid bridge

The liquid bridge is an important model problem in printing processes. We report the experimental results of stretching a highly viscous liquid bridge between two parallel plates. Depending on the stretching speed, a thin liquid bridge exhibits two representative flow regimes. At low stretching speeds, the liquid bridge deforms in a quasi-static manner and no liquid films are observed. When the stretching speed exceeds a critical value, the contact line fails to follow the retracting meniscus, resulting in the deposition of liquid films on the plate. The entrained film is characterized by an annular rim that retracts and grows by collecting the liquid in the film. It is found that the velocity of the receding contact line is weakly decreasing, and the growth of the rim is characterized by a width of wrim∼Ca1/3t1/2, where the capillary number Ca is defined by the stretching velocity and t is the time. The film may not be fully absorbed into the bulk of the liquid bridge before its eventual breakup at high stretching speeds, leading to variations in the liquid transfer ratio of the two plates.

Droplet Physics and Intracellular Phase Separation

Living cells are spatially organized by compartments that can nucleate, grow, and dissolve. Compartmentalization can emerge by phase separation, leading to the formation of droplets in the cell's nucleo- or cytoplasm, also called biomolecular condensates. Such droplets can organize the biochemistry of the cell by providing specific chemical environments in space and time. These compartments provide transient environments, suggesting the relevance of nonequilibrium physics of droplets as a key to unraveling the underlying physicochemical principles of biological functions in living cells. In this review, we highlight coarse-grained approaches that capture the physics of chemically active emulsions as a model for condensates orchestrating chemical processes. We also discuss the dynamics of single molecules in condensates and the material properties of biological condensates and their relevance for the cell. Finally, we propose wetting, prewetting, and surface phase transitions as a possibility for intracellular surfaces to control biological condensates, spatially organize membranes, and exert mechanical forces.

Effects of Cassie-Wenzel wetting transition on two-phase flow in porous media

Wettability is one of the most important factors affecting multiphase flow in porous media. In this study, effects of the dynamic wetting process on two-phase flow displacement are investigated at the pore scale. A time-dependent Cassie-Wenzel wetting transition model is improved and incorporated into the pseudopotential multiphase multicomponent lattice Boltzmann model. With the Cassie-Wenzel wetting transition considered, two-phase flow displacement is simulated in Voronoi porous media with structural disorder and layered characteristics under different capillary number and wetting transition characteristic time. The simulation results show that the wetting transition promotes cooperative pore filling and weakens the effect of nonuniformity of capillary resistance. Under different capillary number, increased wetting transition rate improves the wettability of invading fluid, and thus the saturation of invading fluid is increased. The results also show that the layered structure with decreased pore size along the flow direction compacts the displacement pattern and weakens the viscous fingering, leading to higher displacement efficiency. While in this layered structure, effects of the wetting transition are suppressed due to lower interfacial length between the invading fluid and solid surface. The simulation results provide new insights of the influence of the dynamic wetting transition and on fluid displacement in porous media.

Dynamically adjustable wet ridge for directional liquid movement and controllable coating distribution

Controllable wettability on the surface is widely used in architecture coating, energy transfer, microfluidics, etc. Much progress has been focused on liquid wetting state transition of the artificial surface by external induction, while it is still difficult to realize in situ reversible and controllable transformation of the wetting state in real-time to meet the requirement for complex practical applications. Herein, inspired by the unique functions of the superhydrophobic self-cleaning lotus leaf and long-term preservation of rose petal resulting from special wetting states, we achieve the real-time unidirectional movement of droplet on superhydrophobic ZnO nanoarrays surface via the dynamically adjustable wet ridge. By changing the height of the nanorod and the wetting direction of the solvent, the dynamic wet ridge occurs and controls the existence of air in nanostructure, that is, symmetrical wet ridge can realize in situ reversible wetting state transition, while asymmetrical wet ridge can drive water droplet to move. Based on this, the strategy can be used to effectively adjust wettability of coating solution on superhydrophobic surface and to further obtain controllable coating distribution. This work offers an available strategy to achieve real-time droplet movement and controllable complex coating even on structurally challenging substrate, so as to provide opportunities and positive effects for designing functional materials and devices.

Determination of critical surface tension of wetting of textured water-repellent surfaces

The object of study is aluminum textured with a femtosecond laser and modified with silanes to reduce surface energy. The presence of a special texture on the surface, such as protrusions or hairs, and the inherently low surface energy of the material allow maximizing the water repellency properties. The determination of the critical wetting surface tension by the Zisman method has a pronounced wetting transition point, but the coordinates of this point cannot be accurately predicted. In this work, the Zisman method is considered as a tool for comparing the effectiveness of modifiers for femtosecond laser-textured surfaces. In this work, periodic structures were created by laser ablation on the surface of aluminum, the surface was modified to achieve the Cassie state when wetted with water, and the critical surface tension of wetting was determined by the Zisman method. As a result, it is shown that the Zisman method in combination with the data on the water contact angle values is an effective tool for characterizing the quality of surface modification of textured samples. It is shown that for textured aluminum surfaces, the most effective modifier is silane, which maintains the Cassie wetting state, with a contact angle increased from 155 to 160°. Paraffin has been shown to be a less effective modifier with an implicit wetting plateau and a transition in the range of 30 to 40 mN/m. It is shown that the textures that have acquired water repellency in the course of spontaneous hydrophobization are very unstable to the action of liquids with reduced polarity, although they have high values of the water contact angle. In practice, the creation of water-repellent coatings on aluminum is a promising substrate due to their widespread use in the aviation, automotive, and energy industries due to their high mechanical strength, lightness, and stability of properties.

Wetting transition in the transverse-field spin- 12 XY model with boundary fields

The wetting transition in the transverse-field spin-$\frac{1}{2}$ XY model with opposite boundary fields ${h}_{L}^{x}{h}_{R}^{x}<0$ is studied analytically and numerically. We find that the phase diagram is complex and that the wetting transition is of three types: first, second, and fourth order. The energy gap is obtained analytically, and the magnetization profile, correlation functions, and wetting layer thickness are obtained numerically. For $|{h}_{L}^{x}|,|{h}_{R}^{x}|<{h}_{w}$, a first-order phase transition occurs at ${h}_{L}^{x}=\ensuremath{-}{h}_{R}^{x}$, where ${h}_{w}$ is the continuous wetting transition point. For $|{h}_{R}^{x}|$ larger than ${h}_{w}$, the continuous wetting transition occurs at ${h}_{L}^{x}={h}_{w}$, and vice versa. For $g\ensuremath{\ne}1\ensuremath{-}{\ensuremath{\gamma}}^{2}$, the wetting transition is second order, and commensurate and incommensurate phases occur for $g<1\ensuremath{-}{\ensuremath{\gamma}}^{2}$ and $g>1\ensuremath{-}{\ensuremath{\gamma}}^{2}$, respectively. For $g=1\ensuremath{-}{\ensuremath{\gamma}}^{2}$, the wetting transition is fourth order. For this fourth-order phase transition, the third derivative of the surface magnetization oscillates and diverges near the transition point. The correlation length exponent is $\ensuremath{\nu}=2$, and the dynamic exponent is $z=2$. Thus, this fourth-order transition belongs to a new universality class. The wetting behavior is induced by asymmetric boundary fields ${h}_{L}^{x}=\ensuremath{-}{h}_{R}^{x}$ and its finite-size scaling is discussed.

Orientational Wetting and Topological Transitions in Confined Solutions of Semiflexible Polymers

Despite their considerable practical and biological applications, the link between molecular properties, assembly conditions and self-organized structure in confined polymer solutions remains elusive. Here, we explore the lyotropic nematic ordering of semi-flexible chains in spherical confinement for multiple contour lengths across a wide regime of concentrations. We uncover an original crossover from two distinct quadrupolar states, both characterized by regular tetrahedral patterns of surface topological defects, to either longitudinal, latitudinal or spontaneously-twisted bipolar structures with increasing densities. These transitions, along with the intermediary arrangements that they involve, are attributed to the combination of orientational wetting with subtle variations in their liquid-crystal (LC) elastic anisotropies. Our molecular simulations are corroborated by density functional calculations, and are quantified through the introduction of several order parameters as well as an unsupervised learning scheme for the localization of topological defects. Our results agree quantitatively with the predictions of continuum nematic elasticity theories, and evidence the extent to which the folding of macromolecules and the self-assembly of low-molecular-weight LCs may be guided by the same, universal principles.

Multiscale landscaping of droplet wettability on fibrous layers of facial masks

Liquid mobility is ubiquitous in nature, with droplets emerging at all size scales, and artificial surfaces have been designed to mimic such mobility over the past few decades. Meanwhile, millimeter-sized droplets are frequently used for wettability characterization, even with facial mask applications, although these applications have a droplet-size target range that spans from millimeters to aerosols measuring less than a few micrometers. Unlike large droplets, microdroplets can interact sensitively with the fibers they contact with and are prone to evaporation. However, wetting behaviors at the single-microfiber level remain poorly understood. Herein, we characterized the wettability of fibrous layers, which revealed that a multiscale landscape of droplets ranged from the millimeter to the micrometer scale. The contact angle (CA) values of small droplets on pristine fibrous media showed sudden decrements, especially on a single microfiber, owing to the lack of air cushions for the tiny droplets. Moreover, droplets easily adhered to the pristine layer during droplet impact tests and then yielding widespread areas of contamination on the microfibers. To resolve this, we carved nanowalls on the pristine fibers by plasma etching, which effectively suppressed such wetting phenomena. Significantly, the resulting topographies of the microfibers managed the dynamic wettability of droplets at the multiscale, which reduced the probability of contamination with impact droplets and suppressed the wetting transition upon evaporation. These findings for the dynamic wettability of fibrous media will be useful in the fight against infectious droplets.

The Lattice Model of Particles with Orientation-Dependent Interactions at Solid Surfaces: Wetting Scenarios.

Wetting phenomena in a lattice model of particles having two chemically different halves (A and B) and being in contact with solid substrates have been studied with Monte Carlo methods. The energy of the interaction between a pair of neighboring particles has been assumed to depend on the degree to which the AA, AB and BB regions face each other. In this work, we have assumed that uAA=-1.0 and considered three series of systems with uAB=uBB, uAB=0 and uBB=0. The phase behavior of bulk systems has been determined. In particular, it has been shown that at sufficiently low temperatures the bulk systems order into the superantiferromagnetic (SAF) phase, or into the antiferromagnetic (AF) phase, depending on the magnitudes of AA, AB and BB interaction energies, uAA, uAB and uBB. The SAF structure occurs whenever ϵ=uAA+uBB-2uAB is lower than zero and the AF structure is stable when ϵ is greater than zero. The wetting behavior has been demonstrated to depend strongly on the structure of the bulk condensed phase, the interactions between fluid particles and the strength of the surface potential. In all series, we have found the dewetting transition, resulting from the limited stability of different ordered structures of surface phases. However, in the systems that exhibit the gas-liquid transition in the bulk, the reentrant wetting transition has been observed at sufficiently high temperatures. The mechanism of dewetting and reentrant wetting transitions has been determined. Moreover, we have also demonstrated, how the dewetting transition in the series with uAB=0 is affected by the wall selectivity, i.e., when the interaction between the parts A and B of fluid particles and the solid is different.

Interfacial properties of binary azeotropic mixtures of simple fluids: Molecular dynamics simulation and density gradient theory.

Interfacial properties of binary azeotropic mixtures of Lennard-Jones truncated and shifted fluids were studied by molecular dynamics (MD) simulation and density gradient theory (DGT) in combination with an equation of state. Three binary mixtures were investigated, which differ in the energetic cross interaction parameter that yields different types of azeotropic behavior. This study covers a wide temperature and composition range. Mixture A exhibits a heteroazeotrope at low temperatures, which changes to a low-boiling azeotrope at high temperatures, mixture B exhibits a low-boiling azeotrope, and mixture C exhibits a high-boiling azeotrope. The phase behavior and fluid interfacial properties as well as their relation were studied. Vapor-liquid, liquid-liquid, and vapor-liquid-liquid equilibria and interfaces were considered. Density profiles, the surface tension, the interfacial thickness, as well as the relative adsorption and enrichment of the components at the interface were studied. The results obtained from the two independent methods (MD and DGT) are overall in good agreement. The results provide insights into the relation of the phase behavior, particularly the azeotropic behavior, of simple fluid mixtures and the corresponding interfacial properties. Strong enrichment was found for the mixture with a heteroazeotrope in the vicinity of the three-phase equilibrium, which is related to a wetting transition.

Space of initial conditions and universality in nonequilibrium quantum dynamics

We study analytically the role of initial conditions in nonequilibrium quantum dynamics considering the one-dimensional ferromagnets in the regime of spontaneously broken symmetry. We analyze the expectation value of local operators for the infinite-dimensional space of initial conditions of domain wall type, generally intended as initial conditions spatially interpolating between two different ground states. At large times the unitary time evolution takes place inside a light cone produced by the spatial inhomogeneity of the initial condition. In the innermost part of the light cone the form of the space-time dependence is universal, in the sense that it is specified by data of the equilibrium universality class. The global limit shape in the variable x/t changes with the initial condition. In systems with more than two ground states the tuning of an interaction parameter can induce a transition which is the nonequilibrium quantum analog of the interfacial wetting transition occurring in classical systems at equilibrium. We illustrate the general results through the examples of the Ising, Potts and Ashkin-Teller chains.