Single-component Liquid Research Articles

Catalytic Thermocuring and Synergistic Photothermocuring of Single-Component Acrylate-Grafted Liquid Oligosilazanes.

A novel thermosetting preceramic resin called acrylate-grafted liquid polysilazane (ALSZ) was readily synthesized. The curing behaviors of ALSZ were investigated by the techniques of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and rheological tests. The catalytic thermocuring process was controlled by the addition of a polymerization accelerator composed of a radical initiator (cumene hydroperoxide) and a transition metal catalyst (nickel naphthenate or cobalt naphthenate). Photocuring at room temperature can proceed readily by the addition of photosensitizer 819 (phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide). By combining a radical initiator, a transition metal catalyst, and a photosensitizer, synergistic photothermocuring was achieved, demonstrating advantages such as material shaping at room temperature and low weight loss during curing. The ceramization of the solidified ceramic precursors in an Ar atmosphere was studied using TGA and tube furnace pyrolysis. ALSZs exhibited comparatively high ceramic transformation yields (71-75% at 800 °C). The resulting pyrolytic ceramics maintained their original shape without deformation or foaming expansion. Polysilazanes containing acrylate groups can directly form casting bodies, showing a high static glass transition temperature (>380 °C) by thermomechanical analysis (TMA). FT-IR analyses revealed that multiple reactions are involved in the curing of ALSZ. The results in this paper showed that ALSZ might find prospective applications in material processing, such as additive manufacturing and ceramic-matrix composites.

Puffing/micro-explosion of two-liquid droplets: Effect of fuel shell composition

Theoretical research into the heat and mass transfer, hydrodynamic and physicochemical processes in combustion chambers of gas turbine engines usually implies that multi-component jet fuels are modeled using single-component liquids (saturated or cyclic hydrocarbons) and their substitutes. Due to an insoluble dispersed phase (e.g., water) in their composition, droplets consist of a noncombustible core and a liquid fuel shell. During heating, water droplets coalesce in fuel droplets to produce explosion-triggering volumes of liquid superheated to the boiling point. When heated, these heterogeneous droplets breakup in the micro-explosion and puffing modes. This study reports the numerical simulation results providing the temporal characteristics of heating and evaporation of heterogeneous droplets until puffing/micro-explosive breakup, when varying the composition of the fuel shell in the homologous series of saturated and cyclic (as illustrated by monocycloparaffins) hydrocarbons from C7 to C16. The conducted research has revealed that the variations in the breakup delay times in the homologous series of saturated and cyclic hydrocarbons are nonlinear. The breakup delay rates were found to increase substantially in the boundary points of the investigated series. Mechanisms to control droplet fragmentation delay time were identified for different initial and boundary conditions. A dimensionless complex reflecting the correlation between the critical conditions of composite liquid droplet breakup and the physicochemical properties of the fuel shell components was proposed.

High Performance and Reprocessable In Situ Generated Nanofiber Reinforced Composites Based on Liquid Crystal Polyarylate.

Polymers are playing important roles in the rapid development of triboelectric nanogenerators (TENGs); However, most polymers cannot meet the high requirements of thermomechanical performance; Thus, various polymeric composites are developed for triboelectric layer. These composites are hardly recycled since their reinforcements are unevenly distributed after reprocessing, which limits the sustainable development of TENGs. To solve the above challenges, in situ generated nanofiber reinforced composites (NFRCs) based on single-component liquid crystal polyarylate (LCP) are designed and prepared via a one-step polycondensation. Nonlinear naphthalene (NDA) widens the processing window of LCP without destabilizing the liquid crystal phase. The NDA-rich domains act as a matrix while the NDA-poor domains with higher rigidity form oriented nanofibers to achieve self-reinforcement. The resultant NFRCs possess high glass transition temperature (Tg > 220 °C) and storage modulus (E' = 0.1GPa at 350 °C), which are far beyond existing triboelectric polymers, typically Tg < 110 °C and E' < 0.1MPa (flowable) at 350 °C. Furthermore, NFRC-based TENG exhibits superior electrical output performance and retention rate (>90%) after reprocessing; Overall, this work offers a new design principle to prepare self-reinforced composites, which paves a way to explore high performance materials.

Interfacial vorticity dynamics for Navier–Stokes–Korteweg system: General theory and application to two-dimensional near-wall cavitation bubble

A theory of interfacial vorticity dynamics is developed for the single-component liquid–vapor flows described by the Navier–Stokes–Korteweg equations. The non-ideal equation of state and surface capillarity are collectively considered via the chemical potential gradient force. Explicit formulas of the interfacial enstrophy and chemical potential fluxes are derived to elucidate their generation mechanisms from the interface, which are expressed by using the fundamental surface physical quantities. Then, the transport equation of the Lamb dilatation (namely, the Lamb vector divergence) is rigorously derived, generalizing the previous results of the Lamb-vector dynamics for single-phase incompressible viscous flows. The derived results are evaluated in a near-wall cavitation bubble combined with the van der Waals equation of state. The roles of surface shear stress and vorticity, surface chemical potential gradient, surface acceleration, surface stretching-shrinking motion and dilatational waves are emphasized in generating the interfacial enstrophy and chemical potential fluxes, featured by the strong vorticity concentration, interface deformation and inward-propagating microjet due to the longitudinal pressure difference. These distinct dynamical features observed near the bubble interface are well captured by the spatial distribution of the Lamb dilatation. Analyzing the dynamics of the Lamb dilatation based on the transport equation demonstrates the significance of the high-curvature rotating surface region and its vicinity in view of their dominance to the unsteady diffusion effect of the Lamb dilatation. The present exposition could provide new physical insights into liquid–vapor flows from the perspective of interfacial vorticity dynamics.

A Second Glass Transition Observed in Single-Component Homogeneous Liquids Due to Intramolecular Vitrification.

On supercooling a liquid, the viscosity rises rapidly until at the glass transition it vitrifies into an amorphous solid accompanied by a steep drop in the heat capacity. Therefore, a pure homogeneous liquid is not expected to display more than one glass transition. Here we show that a family of single-component homogeneous molecular liquids, titanium tetraalkoxides, exhibit two calorimetric glass transitions of comparable magnitude, one of which is the conventional glass transition associated with dynamic arrest of the bulk liquid properties, while the other is associated with the freezing out of intramolecular degrees of freedom. Such intramolecular vitrification is likely to be found in molecules in which low-frequency terahertz intramolecular motion is coupled to the surrounding liquid. These results imply that intramolecular barrier-crossing processes, typically associated with chemical reactivity, do not necessarily follow the Arrhenius law but may freeze out at a finite temperature.

Anisotropy in spinodal-like dynamics of unknown water at ice V–water interface

Experimentally demonstrating the existence of waters with local structures unlike that of common water is critical for understanding both the origin of the mysterious properties of water and liquid polymorphism in single component liquids. At the interfaces between water and ices Ih, III, and VI grown/melted under pressure, we previously discovered low- and high-density unknown waters, that are immiscible with the surrounding water. Here, we show, by in-situ optical microscopy, that an unknown water appears at the ice V–water interface via spinodal-like dynamics. The dewetting dynamics of the unknown water indicate that its characteristic velocity is ~ 90 m/s. The time evolution of the characteristic length of the spinodal-like undulation suggests that the dynamics may be described by a common model for spinodal decomposition of an immiscible liquid mixture. Spinodal-like dewetting dynamics of the unknown water transiently showed anisotropy, implying the property of a liquid crystal.

Dynamical coarse-grained models of molecular liquids and their ideal and non-ideal mixtures.

Coarse-grained (CG) simulation models of condensed-phase systems can be derived with well-established methods that perform coarse-graining in space and provide an effective Hamiltonian with which some of the structural and thermodynamic properties of the underlying fine-grained (FG) reference system can be represented. Coarse-graining in time potentially provides CG models that furthermore represent dynamic properties. However, systematic efforts in this direction have so far been limited, especially for moderately coarse-grained, chemistry-specific systems with complicated conservative interactions. With the aim of representing structural, thermodynamic, and dynamic properties in CG simulations of multi-component molecular systems, we investigated a recently introduced method in which the force on a CG particle originates from conservative interactions with surrounding particles and non-Markovian dissipative interactions, the latter introduced by means of a colored-noise thermostat. We examined two different methods to derive isotropic memory kernels required for integrating the corresponding generalized Langevin equation (GLE) of motion, based on the orthogonal dynamics of the FG forces and on an iterative optimization scheme. As a proof of concept, we coarse-grain single-component molecular liquids (cyclohexane, tetrachloromethane) and ideal and non-ideal binary mixtures of cyclohexane/tetrachloromethane and ethanol/tetrachloromethane, respectively. We find that for all systems, the FG single particle velocity auto-correlation functions and, consequently, both the short time and long time diffusion coefficients can be quantitatively reproduced with the CG-GLE models. We furthermore demonstrate that the present GLE-approach leads to an improved description of the rate with which the spatial correlations decay, which is artificially accelerated in the absence of dissipation.

Reentrant 2D Nanostructured Liquid Crystals by Competition between Molecular Packing and Conformation: Potential Design for Multistep Switching of Ionic Conductivity.

Reentrant phenomena in soft matter and biosystems have attracted considerable attention because their properties are closely related to high functionality. Here, we report a combined experimental and computational study on the self-assembly and reentrant behavior of a single-component thermotropic smectic liquid crystal toward the realization of dynamically functional materials. We have designed and synthesized a mesogenic molecule consisting of an alicyclic trans,trans-bicyclohexyl mesogen and a polar cyclic carbonate group connected by a flexible tetra(oxyethylene) spacer. The molecule exhibits an unprecedented sequence of layered smectic phases, in the order: smectic A-smectic B-reentrant smectic A. Electron density profiles and large-scale molecular dynamics simulations indicate that competition between the stacking of bicyclohexyl mesogens and the conformational flexibility of tetra(oxyethylene) chains induces this unusual reentrant behavior. Ion-conductive reentrant liquid-crystalline materials have been developed, which undergo the multistep conductivity changes in response to temperature. The reentrant liquid crystals have potential as new mesogenic materials exhibiting switching functions.

Liquid-liquid phase transition in deeply supercooled Stillinger-Weber silicon.

The existence of a phase transition between two distinct liquid phases in single-component network-forming liquids (e.g. water, silica, silicon) has elicited considerable scientific interest. The challenge, both for experiments and simulations, is that the liquid-liquid phase transition (LLPT) occurs under deeply supercooled conditions, where crystallization occurs very rapidly. Thus, early evidence from numerical equationof state studies was challenged with the argument that slow spontaneous crystallization had been misinterpreted as evidence of a second liquid state. Rigorous free-energy calculations have subsequently confirmed the existence of a LLPT in some models of water, and exciting new experimental evidence has since supported these computational results. Similar results have so far not been found for silicon. Here, we present results from free-energy calculations performed for silicon modeled with the classical, empirical Stillinger-Weber-potential. Through a careful study employing state-of-the-art constrained simulation protocols and numerous checks for thermodynamic consistency, we find that there are two distinct metastable liquid states and a phase transition. Our results resolve a long-standing debate concerning the existence of a liquid-liquid transition in supercooled liquid silicon and address key questions regarding the nature of the phase transition and the associated critical point.

Liquid-liquid transition kinetics in D-mannitol.

The kinetics of the first order liquid-liquid transition (LLT) in a single-component liquid D-mannitol have been examined in detail by the high rate of flash differential scanning calorimetry measurements. By controlling the annealing temperature, the phase X formation from the supercooled liquid is distinguished by either a nucleation-growth or a spinodal-decomposition type of LLT. In the measured time-temperature-transformation curve the portion covering the nucleation-growth type of LLT can be well fitted with a classical nucleation theory analysis.

Perspective on structure-property relationship of room temperature single-component liquid crystals

ABSTRACT Ever since the serendipitous discovery of liquid crystals (LC) by Friedrich Reinitzer in 1888, a significant number of LCs have been synthesised and characterised. The ever-growing LCs emanating from conventional and non-conventional systems find applications in various electronic appliances such as flat-panel TV displays, notebooks, digital cameras, and domestic devices. The room temperature LCs (RT-LCs 20 to ±80 °C), either as single-component/composites, act as a starting point for such applications. Therefore, the quest for such RT-LCs is always valued and carved out as a promising niche for many such devices. Molecular design and the structure-property relationship are the recurrent themes for stable and single-component RT-LCs. The LC molecules starting from simple benzenoids to macrocycles with flexible hydrocarbon chains as spacer/terminal tails needed to be tethered in a precise pattern may lead to potential LCs. To craft stable and single-component RT-LCs, functional groups (nitrile, halogens, nitro, aldehydes, amine, thiol, alcohol, ketone, ester, amide) are frequently employed. RT-LCs with viscosity, dielectric, birefringence, and polarity enables the reduction of the number of components in a composites mixture. This review describes the genesis and importance of the single component RT-LCs, state-of-the-art LC research, perspectives, and new design strategies for venturing into a new horizon.

Calibration Dependencies and Accuracy Assessment of a Silicone Rubber 3D Printer

Silicone rubbers are relatively new in additive manufacturing, with only a few commercial printing services and reports on custom-built printers available. Publications and standards on calibration and accuracy assessment are especially lacking. In this study, the printhead calibration process of a custom-built silicone printer is explained, and a set of test objects is proposed and evaluated. The printer in use is based on an open-source filament printer, capable of multi-material printing with silicone rubbers and thermoplastic polymers. Three different high-viscosity single-component liquid silicone rubbers and one polylactic acid thermoplastic filament were used as printing materials. First, the calibration process of the silicone printhead was conducted, and the dependency of the dosing accuracy on silicone viscosity, nozzle diameter and extrusion speed was evaluated. Second, various test specimens were proposed and printed to characterize the accuracy and geometric limitations of this printer. These test parts contained features such as thin walls, slender towers, small holes and slots, unsupported overhangs and bridges. It was concluded that silicone viscosity strongly affects geometric inaccuracies. Design recommendations were deducted from the results, advising for wall thicknesses above 1 mm, slenderness ratios below 2, bridging lengths below 2 mm and unsupported overhang angles below 30°.

Intrinsic viscuit probability distribution functions for transport coefficients of liquids and solids.

A reformulation of the Green-Kubo expressions for the transport coefficients of liquids in terms of a probability distribution function (PDF) of short trajectory contributions, which were named "viscuits," has been explored in a number of recent publications. The viscuit PDF, P, is asymmetric on the two sides of the distribution. It is shown here using equilibrium 3D and 2D molecular dynamics simulations that the viscuit PDF of a range of simple molecular single component and mixture liquid and solid systems can be expressed in terms of the same intrinsic PDF (P0), which is derived from P with the viscuit normalized by the standard deviation separately on each side of the distribution. P0 is symmetric between the two sides and can be represented for not very small viscuit values by the same gamma distribution formulated in terms of a single disposable parameter. P0 tends to an exponential in the large viscuit wings. Scattergrams of the viscuits and their associated single trajectory correlation functions are shown to distinguish effectively between liquids, solids, and glassy systems. The so-called viscuit square root method for obtaining the transport coefficients is shown to be a useful probe of small and statistically zero self-diffusion coefficients of molecules in the liquid and solid states, respectively. The results of this work suggest that the transport coefficients have a common underlying physical origin, reflecting at a coarse-grained level the traversal statistics of the system through its high-dimensioned potential energy landscape.

Does the second critical-point of water really exist in nature?

In the past decade, a literary phrase “No man's land” has been flooded in the scientific papers. The expression is used to describe a meta-stable region in the phase-diagram that cannot be accessed by experiments. It has been claimed based on the molecular dynamics (MD) simulation that there is a critical point, or the second critical point (SCP), in the “no man's land,” and it has created a big dispute in the field of science. It is proved in the present paper that the hypothesis of SCP is completely against the rigorous theorem of thermodynamics, referred as the Gibbs phase rule. The reason why the simulations have found SCP erroneously is merely because the method violates the requirement which all the statistical-mechanics treatments should satisfy to reproduce the thermodynamics. That is the thermodynamic limit. It is clarified what is the identity of the ``liquid-liquid phase transition'' and SCP in pure liquids, discovered by the simulations and by some experiments. In order to explain the physics of liquid-liquid phase transition observed experimentally in single component liquids, a new concept is proposed.

Kinetic properties and ignition characteristics of fuel compositions based on oil-free and oil-filled slurries with fine coal particles

A difference in the ignition and combustion mechanisms and characteristics was established for fuel compositions based on petroleum waste (used oils) and coal processing waste (high-moisture low-rank coals) with a binding component (polymer thickener), as well as for the individual combustible liquid and solid components used to produce them. Thus, the paper investigates the kinetic combustion characteristics using the isoconversional Friedman method and the temporal ignition characteristics of droplets (particles) under the conditions corresponding to fuel combustion. The data of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were obtained when heating the experimental samples at the rates of 5, 10 and 15 K per minute. It was established that the kinetic combustion characteristics of multi-component fuel compositions differ significantly from those of individual components in a normal state. Unlike single-component liquid and solid fuels, multi-component fuel mixtures based on insoluble liquid components, including those containing fine solid combustible particles, are ignited under the conditions of micro-explosive dispersion when heated in an air medium with a temperature of 973–1273 K.

Self-diffusion in single component liquid metals: a case study of mercury

We report the temperature dependent atomic dynamics in mercury investigated with quasi-elastic neutron scattering between 240 and 350 K. The self-diffusivity follows an Arrhenius behavior over the entire investigated temperature range, with an activation energy of 41.8 ± 1.4 meV. The standard deviation is in the order of 5%, significantly more precise than previously reported measurements in the literature. Similar to alkali metal melts, the self-diffusion coefficient close to the melting point can be predicted with an effective atom radius of 1.37 Å. This shows a dominant contribution from the repulsive part of the interatomic potential to the mass transport. We observed deviations from the Stokes/Sutherland–Einstein relation and indications of an increasing collective nature of the dynamics with decreasing temperature. Thus, a transport mechanism of uncorrelated binary collisions cannot fully describe the temperature dependence of the self-diffusion.

Fluid Flow With Three Upstream Configurations in Freezing Tubes

AbstractThe accumulation of frozen liquid around a central passageway of melt as it flows through a freezing region can make calculations very challenging. To both illustrate and to quantify some of these challenges from freezing, a model equation is developed. It simplifies the solution of Holmes (2007, https://gfd.whoi.edu/wp-content/uploads/sites/18/2018/03/MHolmesGFDReport_30151.pdf) for low Reynolds number single component liquid flow through a long tube that has a wall kept at subfreezing temperature. This model equation is used in conjunction with three different upstream configurations, each with parameters expressing their behavior. Analytical and numerical results give the parameters that have criteria for: the freezing of a compressible upstream reservoir that includes oscillatory behavior; the freezing of flow fed through a constriction with a large upstream pressure, just like a dripping water faucet during winter; the evolution of flow in multiple tubes connected by an upstream manifold, where some tubes end up with full flow and others freeze shut. Numerical runs with 1,000 tubes give a formula for the spacing between actively flowing (non‐frozen) tubes over wide ranges of the two upstream parameters (flow rate and manifold resistance). Results have implications in various areas in earth science. Some are: oscillatory and freezing shut criteria for flow of magma from a compressible region, a criterion for wintertime ice accumulation at natural springs, and the spacing between volcanos.

Exceptionally Wide Thermal Range Enantiotropic Existence of a Highly Complex Twist Grain Boundary Phase in a Pure, Single-Component Liquid Crystal Chiral Dimer.

Twist grain boundary (TGB) phases exhibiting highly frustrated and complex liquid crystal structures have aroused enormous interest because of their close resemblance to superconductors. The remarkable experimental demonstration of their occurrence by Goodby and co-workers paved the way for developing new research endeavors. However, of the several genuine concerns associated with these intriguing structures, their temperature range has been challenging. In this communication, we report the occurrence of the TGB phase with smectic C* blocks (TGBC*) over a vast, unprecedented thermal range of ∼170 °C in a newly synthesized chiral dimer derived from cholesterol. Detailed investigations covering synthesis, characterization, and evaluation of liquid crystallinity with the aid of optical, calorimetric, and X-ray diffraction are presented.

Rydberg-dressed Fermi liquid: Correlations and signatures of droplet crystallization

We investigate the effects of many-body correlations on the ground-state properties of a single-component ultracold Rydberg-dressed Fermi liquid with purely repulsive interparticle interactions in both three and two spatial dimensions. We employed the Fermi-hypernetted-chain Euler-Lagrange approximation and observed that the contribution of the correlation energy on the ground-state energy becomes significant at intermediate values of the soft-core radius and large coupling strengths. For small and large soft-core radii, the correlation energy is negligible and the ground-state energy approaches the Hartree-Fock value. The positions of the main peaks in static structure factor and pair distribution function in the homogeneous fluid phase signal the formation of quantum droplet crystals with several particles confined inside each droplet.

Proper interpretation and overall accuracy of laminar flame speed measurements of single- and multi-component liquid fuels

Low-vapor pressure liquid fuels, particularly kerosene-based fuels, are notoriously difficult to use in precision laboratory-scale flame experiments. This difficulty could result in several sources of uncertainty when preparing fuel-air mixtures for laminar flame speed experiments in constant-volume vessels. To accurately measure the experimental uncertainties in a spherical, laminar flame, n-decane, a component of several popular kerosene-based surrogate fuels was utilized in a methodical study to elucidate and minimize the primary sources of error and to determine a realistic, overall measurement uncertainty. This careful study allowed for isolated analysis of the overall behavior of the fuel (such as whether or not the fuel is condensing) and the accuracy of the instrumentation used. The results show that for the single-component liquid fuel, equivalence ratio could be accurately measured to within φ=±0.03 and flame speed to within 2.79 cm/s. One of the primary sources of discrepancy and confusion when presenting and comparing laminar flame speed data of complex, liquid fuel mixtures is the identification of the average fuel molecule. This seemingly trivial detail is actually a very important property of the fuel because it leads to the determination of φ, which is commonly used as the independent variable of laminar flame speed plots. However, when reported at all, the uncertainty in the average molecular weight of these fuels is on the order of 15%. Because of this large uncertainty, φ is shown to not be the most useful parameter for comparing different data sets. Rather, fuel mole fraction, XFUEL, is much more useful as it describes the overall amount of fuel in the mixture, and plotting laminar flame speeds as a function of XFUEL results in better agreement amongst different data sets from the literature for Jet-A.