Liquid-like Film Research Articles

Jamming to unjamming: Phase transition in cyclodextrin-based emulsions mediated by sodium casein

HypothesisCyclodextrin (CD) can spontaneously build up the solid particle membrane with CD-oil inclusion complexes (ICs) by a self-assembly process. Sodium casein (SC) is expected to preferentially adsorb at the interface to transform the type of interfacial film. The high-pressure homogenization can increase interfacial contact opportunities of the components, which promote the phase transition of the interfacial film. ExperimentsWe added SC by sequential and simultaneous orders to mediate the assembly model of the CD-based films, examined the patterns in which the films adopt phase transitions to retard emulsion flocculation, and studied the physic-chemical properties of the emulsions and films from the structural arrest, interface tension, interfacial rheology, linear rheology, and nonlinear viscoelasticities through Fourier transform (FT)-rheology and Lissajous-Bowditch plots. FindingsThe interfacial and large amplitude oscillatory shear (LAOS) rheological results showed that the films changed from jammed to unjammed. We divide the unjammed films into two types: one is SC dominated liquid-like film, which is fragile and related to droplet coalescence; the other is cohesive SC-CD film, which helps droplet rearrangement and retards droplet flocculation. Our results highlight the potential of mediating phase transformation of interfacial films to improve emulsion stability.

Probing the transient evolution and heat transfer of nascent liquid film during initial condensation

A hybrid theoretical and simulation method is employed to investigate the transient characteristics of heat and mass transfer of nascent liquid film during initial condensation of argon vapor on a subcooled substrate. The method combines a non-equilibrium thermodynamics analysis with molecular dynamics simulations to provide the kinetics and evolution of the atoms. Throughout the evolution process, three different stages can be recognized by the variation of interfacial mass flux. Initially, the solid-vapor interfacial effect is dominated and the argon atoms are adsorbed as clusters and aggregate on the surface. In the transition stage, the mass flux increases and the adsorption behavior almost vanishes, a nascent liquid-like film is formed. When the times exceed a critical value of tc, the condensation process is initiated and the solid-vapor interface is replaced by the vapor-liquid interface. As a result, the mass flux keeps constant. During the adsorption process, the driven force of is theoretical determined through the cluster evolutions. With the decrease of cooling temperature, the mass flux is enlarged and the time for the transition becomes earlier. The mass flux determined from MD simulations coincides well with the theoretical analysis from statistical rate theory. Meanwhile, the spatial evolutions of the atoms are also traced. The atoms in the near wall region present a crystal-like structure. Compared with that in bulk vapor phase, the atoms in the liquid film have a stronger mobility. For the heat and mass transportation, the interfacial temperature jump and the thermal resistance is increased with the increase of cooling temperature. Two independent methods are adopted to obtain the heat and mass fluxes. The slop of the relationship between the heat and mass fluxes shows close agreement with the latent heat of argon, which reveals the occurrence of condensation.

Interfacial Structure and Boundary Lubrication of a Dicationic Ionic Liquid

We report measurements of the normal surface forces and friction forces between two mica surfaces separated by a nanofilm of dicationic ionic liquid using a Surface Force Balance. The dicationic ionic liquid 1,10-bis(3-methylimidazolium)decane di[bis(trifluoromethylsulfonyl)imide] forms a layered structure in nanoconfinement, revealed by oscillatory structural forces. Friction measurements performed at different film thicknesses display quantized friction, i.e., discontinuities in friction as layers are squeezed out and friction coefficients dependent on the number of liquid layers confined between the surfaces. The details of the friction traces indicate a liquidlike film, and, surprisingly, decreasing friction with increasing water content; we discuss possible mechanisms underlying these observations. This latter trait may be helpful in applications where ionic liquid lubricants cannot be insulated against humid environments.

Manipulating and monitoring nanoparticles in micellar thin film superstructures

Understanding the dynamics of discrete self-assembled structures under influence of external triggers is of interest to harvest the potential of nano- and mesoscale materials. In particular, controlling the hierarchical organization of (macro)molecular and nanoparticle building blocks in monolayer superstructures is of paramount importance for tuning properties and characteristics. Here we show how the electron beam in cryo-transmission electron microscopy can be exploited to induce and follow local migration of building blocks and global migration of micellar aggregates inside micrometer-sized superstructures. We employ stroboscopic exposure to heat up and convert the vitrified superstructure into a liquid-like thin film under cryogenic conditions, resulting in controlled evaporation of water that finally leads to rupture of the micelle-containing superstructure. Micelle-embedded nanoparticles prove a powerful tool to study the complex hierarchically built-up superstructures, and to visualize both global movement of individual dendrimicelles and local migration of nanoparticles inside the micellar core during the exposure series.

DEM study of liquid-like granular film from granular jet impact

Dynamic behaviors of a dense granular jet impacting on a circular target are numerically studied by Discrete Element Method (DEM), and the simulation results are compared with experimental data in our previous paper. Firstly, effects of solid fractions of granular jet (xp) and ratios of jet diameter to particle diameter (D/d) on the flow pattern of granular jet impact are investigated. Results show that increasing xp and D/d both increase the interparticle collision frequencies, which decrease the interparticle collision forces and relative velocities, and give rise to the liquid-like granular film, consequently. Secondly, liquid-like wave structures on the granular film are simulated by a granular jet impact with pulsation. Results indicate that the granular wave is primarily determined by the pulsation amplitude and Strouhal number (St) of granular jets. The granular jet impact with pulsation displays distinct wave structures as the optimal St is in the range of 0.2–0.8

Characteristics of granular sheet of dense granular jet oblique impact

Dense granular impinging jets widely exist in natural flow phenomena and industrial processes, such as the rapid heating, cooling or drying, and gasification. It is important to investigate the factors influencing the flow patterns of dense granular impinging jets and reveal the evolution rules of the flow patterns. The dynamic behaviors of the dense granular impinging jets are experimentally studied by a high-speed camera and image processing software of Image J. The effects of the particle diameter, the granular jet velocity (u0) and the solid content of the granular jet (xp) on flow pattern of the granular impinging jet are investigated. Two flow regimes of the dense granular impinging jets, i.e., the liquid-like granular film and the scattering pattern, are identified. The results show that with the increase of the particle diameter and the granular jet velocity, both the solid content of the granular jet and the inter-particle collision frequency decrease, which results in the transition of granular sheet to scattering pattern. With the increase of granular jet velocity, the opening angle of the granular sheet from the side view increases, while the opening angle from the front view increases first and sharply decreases later. The results also show that with the increase of the granular jet velocity, the liquid-like granular film becomes unstable and a non-axisymmetric oscillation appears. And the amplitude and frequency of the liquid-like granular film increase with granular jet velocity increasing, and are significantly affected by particle diameter. The interesting behaviors of the liquid-like surface waves are observed on the granular sheet. The surface waves become remarkable with the increase of the granular jet velocity, and their propagating velocities normalized by the granular jet velocity vary from 0.7 to 0.9. The waves propagating on the granular sheet may emerge, which will reduce the frequencies of the surface waves and increase the surface wavelengths. The results also show that the oscillation frequency of the granular film nearly equals the pulsation frequency of the granular jet. It is indicated that the gas-solid interaction inside the nozzle increases with granular jet velocity increasing, and causes the instability of the granular jet, resulting in the non-axisymmetric oscillation on the granular sheet consequently. The results in this paper present significant knowledge of the dense granular impinging jets and also provide some principles for the applications in dense granular impinging jets in industrial processes.

Reaction between Pyridine and CH3NH3PbI3: Surface-Confined Reaction or Bulk Transformation?

Pyridine molecules have been used to passivate surface Pb2+ sites of CH3NH3PbI3, to recrystallize CH3NH3PbI3, and to bleach CH3NH3PbI3. However, these results contradict each other, as recrystallization and optical-bleach require transformation of bulk CH3NH3PbI3, but surface passivation demands the confinement of the reaction at the surface region. The underlying mechanism for these seemly contradicting results is not yet understood. In this paper, we show, at 25 °C, partial pressure of pyridine vapor is a determining factor for its reaction behaviors with CH3NH3PbI3: one can modify the surface region of CH3NH3PbI3 by using pyridine vapor of pressure 1.15 torr or lower but can transform the whole bulk CH3NH3PbI3 film with a pyridine vapor of 1.3 torr or higher. Our result is the first demonstration that the reaction modes, i.e., surface-confined reaction and bulk transformation, are very sensitive to the partial pressure of under-saturated pyridine vapor. Despite the different reaction behaviors, it is interesting that in all pressure ranges, pyridinium ion is a main product from the reaction between pyridine and CH3NH3PbI3. The bulk transformation is due to the formation of a liquid-like film, which increases the mobility of species to catalyze the reaction between pyridine and CH3NH3PbI3. It is important to note 1.3 torr is much smaller than the saturated vapor pressure of pyridine (20 torr at 25 °C). These findings provide a guidance in applying pyridine and other amines to functionalize and transform CH3NH3PbI3 and other hybrid halide perovskites. It also highlights the critical role of fundamental studies in controllably modifying CH3NH3PbI3.

Thin-film dawsonite in Jurassic coal measure strata of the Yaojie coalfield, Minhe Basin, China: A natural analogue for mineral carbon storage in wet supercritical CO2

A large amount of thin-film dawsonite has developed in coal cleats and also in fractures within the roof sandstone in Jurassic CO2-rich coal measure strata of the Yaojie coalfield, Minhe Basin, China. The CO2 in these strata has been in a supercritical state since natural emplacement. In this study, the Yaojie coalfield is considered a natural analogue site for CO2 capture, utilization, and storage (CCUS). The thin-film dawsonite in coal measure strata was analyzed to investigate the evolution of carbon in supercritical CO2 after CCUS, as it provides a possible example of the formation of carbonate minerals from a wet supercritical CO2 fluid. The cleat- and fracture-filling dawsonite takes the form of white or silver-white radial thin-film crystals (generally <3.2mm in diameter and <20μm in thickness) and appears in a variety of shapes, with the mineral fibers growing divergently within the plane of the film. The thin-film dawsonite within cleats is readily separated from the coal, and its crystal morphology is controlled by the cleat space. The thin-film dawsonite in the roof sandstone does not completely fill fractures, and the morphological characteristics of the surfaces of the mineral crystals indicate that crystal growth was not constrained by the surrounding rock. The sources of the carbon for the cleat-filling dawsonite were magmatic CO2 and CO2 derived from the decomposition of basement marble, which resulted from dynamic–thermal metamorphism of the F19 fault zone. The carbon isotopic compositions of the cleat-filling dawsonite from different carbon sources are transitional, and the carbon source for all of the sandstone fracture-filling dawsonite is the CO2 released from the decomposed basement marble. The morphological and mineralogical characteristics of the thin-film dawsonite show that it most likely nucleated and grew directly in the liquid-like water film formed by wet supercritical CO2 on solid phase surfaces, rather than by epitaxial growth on the rocks surrounding the cleats and fractures, probably via layer-by-layer crystallization. The sodium and aluminum in the dawsonite were derived from formation water. The formation of dawsonite in the coal measure strata of the Yaojie coalfield indicates that some of the free-state CO2, which increases in content due to desorption of the coal matrix, can ultimately be converted into carbonate minerals during CCUS.

Liquid-like granular film from granular jet impact

Dynamic behaviors of dense granular jets impacting a flat target are experimentally studied and numerically simulated using the Discrete Element Method. Effects of the granular jet velocity (u0⩽6.5m/s), the particle diameter (82⩽d⩽350μm), the jet diameter (1⩽D⩽12mm), and the volumetric solid content ratio of the granular jet (0.05⩽xp<0.62) on the flow patterns are investigated. Two patterns were identified: the thin, liquid-like granular film and the diffuse pattern. The profile and thickness of granular films have been characterized. The transition critical parameters and maps of the two patterns are obtained in this work. Results show that the regimes of the granular jet impact are primarily determined by the ratio of jet diameter to particle diameter (D/d) and solid content ratio (xp). A compacted dead zone over the target forms with large D/d and xp, which subsequently causes rapid interparticle inelastic collisions and circular motion of the granular film.

Characteristics of surface waves on the granular sheet of dense granular jet impingement

Dense granular jet impingement widely exists in numerous natural flow phenomena and industrial processes. It is significant to investigate the influencing factors of the flow patterns of dense granular jet impingement and reveal the evolution rules of flow patterns. The dynamic behaviors of dense granular jets impinging on a flat target are experimentally studied by a high-speed camera and image processing software of NIH. The effects of the particle diameter（Dpar), the granular jet velocity（U0) and the solid content of the granular jet（X) on the flow patterns and surface waves of granular sheet are investigated. Two patterns, i.e., the liquid-like granular film and the scattering pattern are identified from the dense granular jet impingement. The results show that with the increase of the particle diameter, the solid content of the granular jet reduces, and the interparticle collision frequency decreases, which results in the granular sheet evolving into the scattering pattern. The opening angle of the granular sheet（) is bigger than that of the liquid sheet, and the granular jet velocity plays an insignificant role in the opening angle. The interesting behaviors of liquid-like surface waves are identified in the granular sheet. The frequency of surface wave of the granular sheet（f) is an order of magnitude smaller than that of the liquid sheet. The surface wave length（) increases and frequency decreases with the increase of radial position, as the surface waves merge during the granular sheet spreading radially. The surface wave spreading velocity normalized by the granular jet velocity is a constant of about 0.4. With the increase of the granular jet velocity, the pulsation of granular jet occurs due to the pressure fluctuation in the discharge process under the effect of gas-solid interaction. The frequencies of surface waves of both the granular sheet and the granular jet pulsation become the same generally. It is indicated that the surface wave is primarily caused by the granular jet pulsation. The results in this paper present the knowledge of the dense granular jet impingement and provide some principles for the steady operation of dense granular jet impingement in industrial process.

Silver Liquid-Like Film Prepared by Self-Assembly for Magnetic Fluid Deformable Mirrors

In this paper, a variety of methods to prepare nanometer thin films, such as LB film method, self-assembly method, vapor deposition method and oil-water two-phase interface deposition method, are first introduced and compared. Then the self-assembly method is used to prepare the silver liquid-like film for the magnetic fluid deformable mirror. The basic principle of configuration of the silver thin films is discussed and a large area of ordered and close-packed multilayer structures of encapsulated silver nanoparticles is fabricated. The results showed that the film has good reflectivity and stability.

Investigation of normal recrystallization and abnormal recrystallization in pure tungsten sheet by EBSD

Normal recrystallization and abnormal recrystallization induced by Ni in pure tungsten (W) sheet were studied by EBSD. It was demonstrated that (001)[11¯0] and (111)[11¯0] textures in the deformed W sheet remain after normal recrystallization, but with lower densities. In addition, (001)[01¯0] and (111)[1¯1¯2] textures arise after recrystallization, which can be explained on the subgrain coarsening recrystallization mechanism. During the abnormal recrystallization of W sheets, grain boundary phase change occurred first between Ni and W, which leads to the formation of liquid-like films on grain boundaries. The occurrence of grain boundary phase change depends mainly on the grain boundary misorientation angle. Grain boundaries with liquid-like film will migrate under the driving force of eliminating deformation storage energy, which gives rise to abnormal recrystallization in W sheets. After abnormal recrystallization, (001)[11¯0] and (111)[11¯0] textures disappeared, leaving only weak texture near (001)[01¯0].

Large-scale solvent driven actuation of polyelectrolyte multilayers based on modulation of dynamic secondary interactions.

Polyelectrolyte multilayers (PEMs), assembled from weak polyelectrolytes, have often been proposed for use as smart or responsive materials. However, such response to chemical stimuli has been limited to aqueous environments with variations in ionic strength or pH. In this work, a large in magnitude and reversible transition in both the swelling/shrinking and the viscoelastic behavior of branched polyethylenimine/poly(acrylic acid) multilayers was realized in response to exposure with various polar organic solvents (e.g., ethanol, dimethyl sulfoxide, and tetrahydrofuran). The swelling of the PEM decreases with an addition of organic content in the organic solvent/water mixture, and the film contracts without dissolution in pure organic solvent. This large response is due to both the change in dielectric constant of the medium surrounding the film as well as an increase in hydrophobic interactions within the film. The deswelling and shrinking behavior in organic solvent significantly enhances its elasticity, resulting in a stepwise transition from an initially liquid-like film swollen in pure water to a rigid solid in pure organic solvents. This unique and recoverable transition in the swelling/shrinking behaviors and the rheological performances of weak polyelectrolyte multilayer film in organic solvents is much larger than changes due to ionic strength or pH, and it enables large scale actuation of a freestanding PEM. The current study opens a critical pathway toward the development of smart artificial materials.

Optical Tracking of Single Ag Clusters in Nanostructured Water Films

The spatial diffusion and size distribution of monodisperse silver nanoclusters synthesized via Ag(I) carboxylate in zeolite Y cages are investigated in nanostructured water films on silicon dioxide (SiO2) and mica surfaces with optical and atomic force techniques. Subnanometer clusters escaping the zeolite Y cage show a strong and photostable fluorescence emission in the visible range and allow for optical single-cluster tracking. Heterogeneous diffusion dynamics reflect the transition from an ice-like to a liquid-like water film as a function of film thickness. The contributions of the different diffusion coefficients strongly correlate with the water film thickness and the chemical composition of the interface. The heterogeneity of the diffusion is caused by ad- and desorption of Ag clusters to silanol groups at the SiO2 interface which couple vibronically to the Ag clusters as can be seen from single cluster fluorescence spectra.

Adsorption of sugar surfactants at the air/water interface

The adsorption isotherms of n-decyl-β-d-glucoside (β-C10G1) as well as various n-alkyl-β-d-maltosides (β-CnG2) with n=8, 10, 12 and 14 were determined from surface tension measurements. Based on the analysis of the adsorption isotherms, the total free energy change of adsorption was determined and a novel method was proposed to determine the maximum adsorbed amount of surfactant. It can be concluded that the driving force for adsorption first increases with increasing adsorbed amount of the sugar surfactants and then levels off in a plateau. This peculiar behaviour is interpreted as formation of a thin liquid-like alkane film of overlapping alkyl chains at the air/water interface once a certain adsorbed amount is exceeded. The driving force of adsorption depends on the alkyl chain length only and is not affected by the type of the head group. The hydrophobic contribution to the standard free energy change of adsorption was compared with the values of sodium alkylsulfate and alkyltrimethylammonium bromide surfactants. This comparison reveals that the hydrophobic driving force of adsorption is the largest for the sodium alkylsulfates, whereas it is the same for the sugar surfactants and the alkyltrimethylammonium bromides.

Study on Freezing Characteristics of Supercooled Water Droplets Impacting on Solid Surfaces

An experimental study was carried out to investigate the freezing characteristics of supercooled water droplets impacting on solid surfaces. Each water droplet was supercooled on the inside surface of a waterrepellent guideway in a cooled air environment and then blasted horizontally by a jet of pressurized cooled air to impact on the vertical surface of a test block. The deformation and freezing of the droplets were observed using a high-speed camera. The droplets were frozen under varying conditions of air temperature, surface temperature, impact velocity and droplet volume. The results indicated that the freezing behavior of a droplet was strongly affected by the condition of the solid surface. Further, the results revealed that the supercooling solidification process consisted of two steps with two greatly different time scales. Finally, it was shown that the freezing behavior of an ice layer was affected by the presence of a liquid-like thin film.

Photoinitator surface segregation induced instabilities from polymerization of a liquid coating on a rigid substrate

Periodic wrinkled surfaces have generated significant interest over the past decade as these structures can be easily fabricated over large areas with minimal fabrication cost, but these structures have generally been limited to thin films on soft elastomeric substrates, which limits their general applicability and utility. Here we present a simple methodology to generate wrinkled surfaces on rigid substrates by surface segregation of a photocatalyst. Upon ultraviolet light (UV) induced photopolymerization, increased catalyst concentration yields a cross-linked layer at the free surface that is supported on top of a more liquid-like bulk film due to differences in polymerization rate. Further polymerization of the underlayer provides the requisite mechanical stress (contraction due to polymerization) to create a wrinkled pattern. A system based upon the renewable monomer, furfuryl alcohol, that is cross-linked with a photoacid generator, triphenyl sulfonium triflate, is utilized to illustrate this concept. Moreover, the polymerized furfuryl alcohol can be transformed into amorphous carbon by heating at elevated temperatures in an inert environment. The role of photoacid generator concentration and substrate temperature on the wrinkle formation and morphology is presented. Finally, exposure through a simple mask can generate hierarchical structures with the wrinkled structure conforming to the geometric constraints of the photopatterned area, including curvilinear structures. This photocatalyzed surface segregation-based methodology provides a promising route to the facile fabrication of microstructured surfaces based upon the wrinkling instability.

In Situ Infrared Spectroscopic Study of Forsterite Carbonation in Wet Supercritical CO2

Carbonation reactions are central to the prospect of CO(2) trapping by mineralization in geologic reservoirs. In contrast to the relevant aqueous-mediated reactions, little is known about the propensity for carbonation in the key partner fluid: supercritical carbon dioxide containing dissolved water ("wet" scCO(2)). We employed in situ mid-infrared spectroscopy to follow the reaction of a model silicate mineral (forsterite, Mg(2)SiO(4)) for 24 h with wet scCO(2) at 50 °C and 180 atm. The results show a dramatic dependence of reactivity on water concentration and the presence of liquid water on the forsterite particles. Exposure to neat scCO(2) showed no detectable carbonation reaction. At 47% and 81% water saturation, an Ångstrom-thick liquid-like water film was detected on the forsterite particles and less than 1% of the forsterite transformed. Most of the reaction occurred within the first 3 h of exposure to the fluid. In experiments at 95% saturation and with an excess of water (36% above water saturation), a nanometer-thick water film was detected, and the carbonation reaction proceeded continuously with approximately 2% and 10% conversion, respectively. Our collective results suggest constitutive links between water concentration, water film formation, reaction rate and extent, and reaction products in wet scCO(2).

Sorption of molybdate anions by a quasi-liquid film on the surface of dispersed ice

Molybdate anion sorption on the surface of dispersed ice in the presence of KCl as a background electrolyte is studied depending on the pH and temperature. The revealed dependences are interpreted in terms of the properties of a liquid-like film present on the surface of the ice.

How pre-melting on surrounding interfaces broadens solid–liquid phase transitions

Phase transitions occur when the chemical potentials (including bulk and interfacial contributions) of two phases are equal. For systems with large interfaces, such as thin films or small particles, their interfacial properties strongly affect the phase behaviour. This dependence is important in fundamental and applied science (sintering, nucleation) but many details are still poorly understood owing to the scarcity of quantitative experimental data. Here, we use solid alkane domains that are one monolayer thick and deposited on a substrate to investigate and quantify the influence of the interface on the solid–liquid phase transition. The domains melt gradually below the bulk melting point of alkane. They coexist with a ‘pre-molten’ liquid-like film of variable temperature-dependent thickness. Molecules interchange reversibly between film and domains, thereby converting transition enthalpy into interfacial energy. (Thus, we obtain details of the intermolecular interactions within the adjacent film.) We show that irrespective of its dimensionality or confinement, every solid will melt (partially) and spread out at temperatures below its bulk melting point if its liquid wets the adjoining interface.