Liquid Transition Research Articles

Preparation and characterization of stable methyl myristate−in−water nanoemulsions as advanced working fluids for cooling systems

Phase change material emulsions (PCME) have gained increasing scientific interest due to their potential to enhance the storage capability of thermal facilities. Herein we present the design and characterization of oil−in−water (O/W) nanoemulsions by employing a dispersed phase mixture (2–12 wt%) enriched in methyl myristate as phase change material. The emulsifier and dispersed phase compositions were optimized based on dynamic light scattering and calorimetric analyses. A two−surfactant formulation composed of sodium dodecyl sulfate and BrijTM S2 (20:49 in weight) was selected to produce stable colloidal dispersions of a methyl stearate:n–hexadecane:methyl myristate mixture (at a mass proportion of 1:3:36) in water. No phase separation or significant growth in emulsified droplet size was detected under storage conditions or when the slurries were subjected to different heating−cooling cycles. The melting/crystallization transitions, rheological behavior, thermal conductivity and density of optimized nanoemulsions were experimentally investigated in order to further understand how the concentration and physical state of suspended droplets may influence those thermal and physical properties. According to differential scanning calorimetry studies, slurries showed moderate subcooling degrees (∼3 °C), even though their solid−liquid transitions extended over a slightly wider range of temperatures than the same mixture used as the dispersed phase but in bulk−form. The shear−thinning character observed for developed nanoemulsions at low temperatures disappeared with the melting of suspended droplets. Considering an operating temperature interval of 15 °C around melting−crystallization phase changes, the 12 wt% optimized suspension presented a storage capacity 18 % higher than that of water under the same conditions. Furthermore, thermal reliability tests verified that phase change characteristics did not significantly changed after 8 months of storage and throughout 500 thermal cycles.

Interaction- and phonon-induced topological phase transitions in double helical liquids.

Helical liquids, formed by time-reversal pairs of interacting electrons in topological edge channels, provide a platform for stabilizing topological superconductivity upon introducing local and nonlocal pairings through the proximity effect. Here, we investigate the effects of electron-electron interactions and phonons on the topological superconductivity in two parallel channels of such helical liquids. Interactions between electrons in different channels tend to reduce nonlocal pairing, suppressing the topological regime. Additionally, electron-phonon coupling breaks the self duality in the electronic subsystem and renormalizes the pairing strengths. Notably, while earlier perturbative calculations suggested that longitudinal phonons have no effect on helical liquids themselves to the leading order, our nonperturbative analysis shows that phonons can induce transitions between topological and trivial superconductivity, thereby weakening the stability of topological zero modes. Our findings highlight practical limitations in realizing topological zero modes in various systems hosting helical channels, including quantum spin Hall insulators, higher-order topological insulators, and their fractional counterparts recently observed in twisted bilayer systems.

Exploring the Mpemba effect: a universal ice pressing enables porous ceramics.

Piezoceramics with global porosity and local compaction are highly desired to exploit the combination of mechanical and electrical properties. However, achieving such a functional combination is challenging because of the lack of techniques for applying uniform pressure inside porous ceramic green parts. Nature provides many examples of generating strong forces inside the macro and micro channels via the state transformation of water. Inspired by these phenomena, we present a technique of "ice and fire", that is, water freezing (ice pressing) and high-temperature sintering (fire), to produce ideal porous piezoceramics. We introduce a new compaction method called the "ice pressing method", which manipulates liquid phase transition for compaction. This method has several advantages, including uniform pressure distribution, a wide pressure range, high effectiveness, and selective freezing. It can generate an ultrahigh pressure of up to 180 MPa on the piezoceramic green skeletons in minutes while retaining their functional pore structures. By exploiting the Mpemba phenomenon, we further accelerate the compaction procedure by 11%. The first ice-pressed and second fire-consolidated lead zirconate titanate (PZT) ceramics are highly densified and exhibit an outstanding piezoelectric response (d33 = 531 pC N-1), comparable to conventional pressed bulk counterparts and 10-20 times higher than those of unpressed materials. The novel ice pressing method breaks the limitation of lacking a compaction technique for porous ceramics. The versatile and effective ice pressing method is a green and low-cost route promoting applications in sensors, acoustics, water filtration, catalyst substrates, and energy harvesting.

Possibilities and limitations of convolutional neural network machine learning architectures in the characterisation of achiral orthogonal smectic liquid crystals.

Machine learning is becoming a valuable tool in the characterisation and property prediction of liquid crystals. It is thus worthwhile to be aware of the possibilities but also the limitations of current machine learning algorithms. In this study we investigated a phase sequence of isotropic - fluid smecticA - hexatic smectic B - soft crystal CrE - crystalline. This is a sequence of transitions between orthogonal phases, which are expected to be difficult to distinguish, because of only minute changes in order. As expected, strong first order transitions such as the liquid to liquid crystal transition and the crystallisation can be distinguished with high accuracy. It is shown that also the hexatic SmB to soft crystal CrE transition is clearly characterised, which represents the transition from short- to long-range order. Limitations of convolutional neural networks can be observed for the fluid to hexatic SmA to SmB transition, where both phases exhibit short-range ordering.

Unraveling solid–liquid phase transition and microstructural coarsening of semi-solid Al0.8Co0.5Cr1.5CuFeNi HEA with dual globules for thixoforming application

Multi-phase HEAs typically have potential of semi-solid processing due to wide semi-solid range. For thixoforming route of semi-solid processing (SSP), the semi-solid billet preparation by semi-solid isothermal heat treatment (SSIT) is one of the most important process steps. This work focuses on the microstructure evolution during SSIT of a semi-solid Al0.8Co0.5Cr1.5CuFeNi HEA with dual globules for thixoforming application. This semi-solid HEA contains BCC(B2), FCC globules and Cu-rich liquid film. Solidified liquid follows K-S, epitaxial orientation relationship withneighboringBCC(B2) and FCC globules. Solutionizing point for B2 phase is higher than roughly 1175 °C, and complete disordering of BCC(B2) globule occurs at 1225 °C. While, FCC globule persists stable disordered solid solution. Solid-liquid phase transition of globules provides liquid film proliferation. CALPHAD simulation on the “hypothetical” alloy system corresponding to component constitution of individual globule successfully forecasted solid–liquid phase transition. Coupling coarsening inhibition effects, including sluggish diffusion in globules, Cu-rich liquid film as inhibitory barrier, heterogeneous globule as obstacle, account for extremely sluggish microstructural coarsening (coarsening rate is only 2.44–11.25 μm3/s). Finally, through forming ofexemplar component, intriguing potential for SSP application in component manufacturing was verified.

Degradable Superhydrophobic Coatings Using the Solid–Liquid Transition of a Multilayer Structure near Body Temperature

Degradable Superhydrophobic Coatings Using the Solid–Liquid Transition of a Multilayer Structure near Body Temperature

Large-scale molecular dynamics simulations of bubble collapse in water: Effects of system size, water model, and nitrogen

Molecular dynamics simulations in the microcanonical ensemble are performed to study the collapse of a bubble in liquid water using the single-site mW and the four-site TIP4P/2005 water models. To study system size effects, simulations for pure water systems are performed using periodically replicated simulation boxes with linear dimensions, L, ranging from 32 to 512 nm with the largest systems containing 8.7 × 106 and 4.5 × 109 molecules for the TIP4P/2005 and mW water models, respectively. The computationally more efficient mW water model allows us to reach converging behavior when the bubble dynamics results are plotted in reduced units, and the limiting behavior can be obtained through linear extrapolation in L−1. Qualitative differences are observed between simulations with the mW and TIP4P/2005 water models, but they can be explained by the models’ differences in predicted viscosity and surface tension. Although bubble collapse occurs on time scales of only hundreds of picoseconds, the system sizes used here are sufficiently large to obtain bubble dynamics consistent with the Rayleigh–Plesset equation when using the models’ thermophysical properties as input. For the conditions explored here, extreme heating of the interfacial water molecules near the time of collapse is observed for the larger mW water systems (but the model underpredicts the viscosity), whereas heating is less pronounced for the TIP4P/2005 water systems because its larger viscosity contribution slows the collapse dynamics. The presence of nitrogen within the bubble only starts to affect bubble dynamics near the very end of the initial collapse, leading to an incomplete collapse and strong rebound for the mW water model. Although nitrogen is non-condensable at 300 K, it becomes highly compressed and reaches a liquid-like density near the collapse point. We find that the dissolution of nitrogen is much slower than the movement of the collapsing water front, and the re-expansion of the dense nitrogen droplet gives rise to bubble rebound. The incompatibility of the collapse and dissolution time scales should be considered for continuum-scale modeling of bubble dynamics. We also confirm that the diffusion coefficient for dissolved nitrogen is insensitive to pressure as the liquid transitions from a compressed to a stretched state.

Thermal–electrical coupling analysis based on solid–liquid phase transition theory of single-turn coil

Single-turn coil (STC) is a destructive pulse magnet aiming at a 100–300 T ultra-high magnetic field. A thermal–electrical coupling model, in which the solid–liquid phase transition process is considered, is proposed. The effects of solid–liquid phase transition on pressure, temperature, and electrical conductivity are investigated. The results show that the compressed and stretched regions coexist simultaneously, and the distribution of both regions changes with time during discharging. Moreover, the region with the highest current density is inside the conductor, since the phase transition reduces the electrical conductivity of the region near the inner surface of STCs. By comparison, the simulation results are highly consistent with the measured data, and the necessity of considering the phase transition process is validated. The results obtained in this work are helpful for understanding the thermodynamic process of STCs during discharge.

Solid-liquid phase transition temperature prediction of alloys based on machine learning key feature screening

A machine learning strategy is proposed based on the demand for prediction of solid-liquid phase transition temperature properties of multi-component precious metal alloys. Firstly, the candidate feature set are constructed by mathematical operation of the physical and chemical parameters of the material according to the chemical ratio of the alloy chemical formula. Then, a novel feature selection framework of correlation screening → genetic algorithm screening → feature weight ranking → exhaustive screening is proposed to effectively identify key feature combinations affecting solid-liquid phase transition temperature. Finally, the support vector regression algorithm is used to establish the "key feature combination-solid phase transition temperature" model with an error less than 9.83% and the "key feature combination-liquid phase transition temperature" model with an error less than 9.35%. The proposed new feature framework overcomes the inability of conventional feature selection techniques to simultaneously meet the requirements of interpretability, low computational complexity, and strong feature generality. Moreover, the comprehensive equilibrium complexity and accuracy (R2) constructed "solid temperature-key feature combination" with an error of less than 6.50% and "liquid phase transition temperature-key feature combination" with an error of less than 6.71 % by symbolic regression algorithm, which strengthened the understanding of the influence of key independent variable feature parameters on solid-liquid phase transition temperature prediction. This established machine learning strategy has excellent reliability in the prediction of solid-liquid phase transition temperature of multi-component alloys, and the proposed feature selection framework is expected to develop into a new feature selection technique.

Exploring the Potential Mechanism of Action of Piperine against Candida albicans and Targeting Its Virulence Factors.

Plant-derived compounds have proven to be a source of inspiration for new drugs. In this study, piperine isolated from the fruits of Piper nigrum showed anti-Candida activity. Furthermore, the mechanisms of action of piperine and its impact on virulence factors in Candida albicans, which have not been comprehensively understood, were also assessed. Initially, piperine suppressed the hyphal transition in both liquid and solid media, hindered biofilm formation, and resulted in observable cell distortions in scanning electron microscope (SEM) samples, for both fluconazole-sensitive and fluconazole-resistant C. albicans strains. Additionally, the morphogenetic switches triggered by piperine were found to rely on the activity of mutant C. albicans strains. Secondly, piperine treatment increased cell membrane permeability and disrupted mitochondrial membrane potential, as evidenced by propidium iodine and Rhodamine 123 staining, respectively. Moreover, it induced the accumulation of intracellular reactive oxygen species in C. albicans. Synergy was obtained between the piperine and the fluconazole against the fluconazole-sensitive strain. Interestingly, there were no hemolytic effects of piperine, and it resulted in reduced cytotoxicity on fibroblast cells at low concentrations. The results suggest that piperine could have a dual mode of action inhibiting virulence factors and modulating cellular processes, leading to cell death in C. albicans.

The Activation Energy of Viscous Flow and Liquid–Liquid Structure Transition in Co-B Alloys

The temperature dependences of the kinematic viscosity during heating and cooling have been investigated in Co-B melts with a boron content of up to 30.8 at. A liquid–liquid structural transition was found, which is accompanied by an increase in the activation energy and cluster size, as well as a significant decrease in the density of the melt. The liquid–liquid structural transition was associated with the formation of clusters with a short-range order of Co23B6 in the intermediate temperature region. At low and high temperatures, clusters of the order of an atomic size are active participants in the viscous flow. It was shown that with an increase in the cluster size, the activation energy increases and the viscosity of melts decreases. The formation of large Co23B6 clusters during the cooling of melt with low boron content leads to undercooling and the appearance of the transition temperature region with high activation energy, although this region does not exist during the heating stage.

Investigation of the smashing characteristics induced by energy distribution of CO2 BLEVE for coalbed methane recovery

Failure in the near field of coal by liquid CO2 phase transition blasting (LCO2-PB) is the major reason for fracturing performance and enhancing coalbed methane (ECBM) recovery. Features to clarify this failure are of significant importance for the field projects. Some studies have revealed that the energy of LCO2 releasing can determine the damage feature to some extent. This study was therefore initiated to investigate the effect of BLEVE energy on the fracturing performance of LCO2-PB in coal. A series of LCO2-PB fracturing tests was carried out on hard and soft coal to examine the effect of CO2 BLEVE energy on fracture morphology. It was obtained that, compared with fractal dimension of hard coal under lower import energy (623.48 kJ) is around 2.17, the higher import energy (831.36 kJ) provides a larger fractal dimension (2.32), especially for high rupture pressure (95 MPa), which make fragments smash into a smaller radial. Although higher input energy favours a large superfluous energy density for any coal types, soft coal represents a stronger tendency to fracture in the stress drop stage. Lower input energy in hard coal seam products a longer main fracture, and excellent fracturing in soft coal prefers the higher import energy.

Drag on a plate perpendicular to the flow of an elasto-viscoplastic fluid

The flow with no inertia of an elasto-viscoplastic fluid around a plate perpendicular to the flow direction was considered. Firstly, experiments were performed with a model yield stress fluid, an aqueous Carbopol gel. The viscoelastic behavior of the fluid is identified by steady and transient rheological measurements. The drag force on the plate has been measured as a function of the plate velocity in steady state and in relaxation after stopping the movement. The role of the initial stress state in the fluid was highlighted. Secondly, numerical simulations were carried out using the finite element method with Lagrangian integration points. As a first approach, the elasto-viscoplastic behaviour of the gel has been simplified by a constitutive equation based on the Maxwell and Herschel-Bulkley models. The solid–liquid transition is defined by the von Mises criterion. The comparison between experimental and numerical data are quite satisfactory.

Regulating thermal dynamics and gas transport of metal‐oraganic framework glass through silver composites

AbstractMetal–organic framework (MOF) glass is a versatile and processible material that retains its porous nature while transitioning between liquid and solid states. Incorporating composites into MOF glass can enhance its functionalities, but the effect of the added material on the solid–liquid phase transition of MOF glass remains understudied. This research explores the impact of silver ions on the properties of ZIF‐62 glass, revealing their influence on phase conversion at varying ligand concentrations. The presence of silver enhances gas separation processes, particularly improving CO2 and hydrocarbon separation selectivity compared to pure ZIF‐62 glass. These findings provide valuable insights for composite integration and highlight the potential of AgZIF‐62 glass in gas separation applications. Furthermore, this work paves the way for processing functional AgZIF‐62 glass films, enabling diverse applications such as gas separation, film catalysis, and antimicrobial glass.

Effect of Shear History on Solid-Liquid Transition of Particulate Gel Fuels.

Investigating the structural evolution of particulate gels is a very challenging task due to their vulnerability and true flow characteristics. In this work, deeper insight into the rheological properties of gel fuels filled with fumed silica (FS) and aluminum microparticles (Al MPs) was gained by changing shear procedures. Firstly, the flow curves were found to no longer follow the monotonic power law and exhibited subtle thixotropic responses. As the shear rate increased, the gel structure underwent a transition from local shear to bulk shear in the nonlinear region after yielding. This finding reveals the prevalence of nonideal local shear in industry. Secondly, the time-dependent rheological responses demonstrated that the strength spectrum of gel fuels depends on the applied shear rate, with stress relaxation more easily observed at lower shear rates. Those results involved the structural disruption, recovery, and equilibrium of particulate gels from two scales of shear rate and shear time.

Test and Analysis of the Heat Exchanger for Small Ocean Thermal Energy Power Generation Devices

The application of ocean thermal energy conversion is an effective method to extend underwater vehicles’ running times and operating ranges, and the solid–liquid phase transition of the phase change material (PCM) in the heat exchanger is a key process for underwater vehicles to collect ocean thermal energy. This study proposes a heat exchanger structure for a small-size thermal energy power generation device and establishes the heat transfer model for the heat exchanger. Simulations were conducted considering convective heat transfer, and the obtained results demonstrated the feasibility of the designed structure. A prototype of the heat exchanger was developed, and physical experiments were conducted to validate the performance of the prototype. The results show that the melting process of the heat exchanger can be completed within 6 to 12 h, the solidification process can be completed within 3 to 7 h, and the heat transfer time decreases with the increase in temperature difference, verifying the compatibility with the underwater vehicles’ working patterns. Moreover, the heat exchanger could theoretically extend their lifetime. The results can provide a reference for the structural design and optimization of the heat exchanger for small ocean thermal energy power generation devices in the future.

Molecular dynamics simulation of the effect of carbon nanotubes on liquid argon phase transition behavior on the platinum plate

The effect of varying single-walled carbon nanotubes (SWCNTs) volume fractions on the phase transition behavior exhibited by liquid argon was investigated in this study. The thermodynamic behavior of SWCNTs/Ar nanofluid was performed by molecular dynamics simulation realized through the LAMMPS computational package. Physical parameters (e.g., thermal conductivity, heat flow, total energy, fluid temperature, gas phase atomic number, and density) were examined to investigate the atomic characteristics exhibited by nanofluid with volume fractions of carbon nanotubes (CNTs) ranging from 0 vol% (pure liquid) to 2.28 vol%. As revealed by the result of the simulation analysis, the rate of temperature rise can be increased, and the transition period can be shortened through the incorporation of CNTs into the base fluid. When the CNTs volume fraction ranged from 0.57 vol% to 1.14 vol%, the thermal conductivity was enhanced by a maximum of 75 %, from 0.0507 W/mK for pure liquid argon to 0.089 W/mK for CNTs/Ar nanofluid. The thermal conductivity was reduced under CNTs volume fraction of over 1.71 vol%. Lastly, a conclusion was drawn in this study, i.e., introducing a proper proportion of CNTs into Ar fluid can lead to the effective improvement of the thermodynamic performance of the nanofluid.

Pressure Effect on Thermodynamic Quantities for the Solid-Liquid Phase Transition in n-tridecane, n-hexadecane and n-octadecane

The pressure effect is investigated regarding the solid – liquid equilibria (SLE) in n-alkanes. Using the Landau phenomenological model, the pressure dependences of the thermodynamic functions are predicted and the phase diagrams are constructed for the solid – liquid transitions in the binary mixtures of n-alkanes. The experimental data from the literature are used for the phase diagrams in the mixtures.
 Our fits for the phase diagrams are reasonably good. Regarding the cubic dependence of the concentration (T-X, P-X) and the linear dependence of the pressure (P-T) on the temperature, our results show that the n-tridecane is distinguished from the other mixtures due to its lowest freezing temperature (T_1=291.08 K) and correspondingly higher concentration (x_1=0.1982). It is found that the divergence behaviour of the heat capacity (C) with the critical exponent 1⁄2 from the extended mean field model is in particular more apparent at the room temperature (293.15 K) at various pressures for the solid – liquid transition. This is accompanied with the pressure dependences of the order parameter, susceptibility, entropy and enthalpy for those mixtures as studied here.

Cephalopod-inspired polymer composites with mechanically tunable infrared properties

Cephalopods have evolved an all-soft skin that can rapidly display colors for protection, predation, or communication. Development of synthetic analogs to mimic such color-changing abilities in the infrared (IR) region is pivotal to a variety of technologies ranging from soft robotics, flexible displays, dynamic thermoregulatory systems, to adaptive IR disguise platforms. However, the integration of tissue-like mechanical properties and rapid IR modulation ability into smart materials remains challenging. Here, by drawing inspiration from cephalopod skin, we develop an all-soft adaptive IR composite that can dynamically change its IR appearance upon equiaxial stretching. The biomimetic composite is built entirely from soft materials of liquid metal droplets and elastic elastomer, which are analogs of chromatophores and dermal layer of cephalopod skin, respectively. Driven by externally applied strains, the liquid metal inclusions transition between a contracted droplet state with corrugated surface and an expanded platelet state with relatively smooth surface, enabling dynamic variations in the IR reflectance/emissivity of the composite and ultimately resulting in reversible IR adaption. Strain-actuated flexible IR displays and pneumatically-driven soft devices that can dynamically manipulate their IR appearance are demonstrated as examples of the applicability of this material in emerging adaptive soft electronics.

Influence of the dispersed silver nanoparticles size and concentration on the properties of 6CB nematic

ABSTRACT We study the effects of concentration and size of the doped silver nanoparticles on material properties of 6CB nematic: 4-hexyl-4’-cyanobiphenyl using electrical, dielectric measurements along with the polarising microscopy methods. We show that the dispersed NPs do not affect the nematic-isotropic liquid transition temperature. We report that the doped NPs decrease the dielectric anisotropy, elasticity and viscosity of the material. We attribute this behaviour to the fact that the dispersed NPs lower the orientational order parameter of the nematic. However, the threshold voltage stays almost unaffected by the doped NPs and the switching-off time is decreased only at certain NPs concentration. Using our measured data, we test the validity of the predicted by the classical Maier-Saupe theory, linear dependence of the elasticity vs the square root of the order parameter. We show that while for the pure sample the mentioned dependence follows the classical prediction, the dispersed samples elasticity shows anomalous behaviour. We report that the mentioned dependence predicted by Gelbart-Ben Shaul theory fits well with the doped samples measured data.