Dilute Liquids Research Articles

Multi-scale modelling of dilute viscoelastic liquids: Atomistic to mesoscale mapping of polymer solutions

A framework predicting the rheological (storage and loss moduli, first normal stress coefficient, and relaxation time) and transport (viscosity, diffusivity) properties of non-Newtonian dilute polymer solutions at mesoscales (e.g. ∼ns to μs) from the atomistic-scale molecular behaviour is presented. More specifically, the rheological behaviour differences of OCP and PMA polymer solutions in PAO-2 oil are simulated using both atomistic molecular dynamics (MD) and many-body dissipative particle dynamics (mDPD) within a temperature range of 313–373 K. The simulation methodology described is able to distinguish itself from the standard DPD model by accurately reproducing the shear-thinning with high sensitivity, as seen in the atomistic MD simulations at high shear rates (e.g. 108−1013 s−1). It is shown that the model is well-suited to compute properties such as first normal stress differences and relaxation times that are difficult to estimate at atomistic scales due to the low signal-to-noise ratio. Moreover, the Schmidt numbers (>103) are predicted with high accuracy when compared with the values from atomistic-scale simulations. The proposed model is able to predict relaxation times of dilute polymer mixtures that are difficult to be obtained using state-of-the-art rheometers. Finally, it is found that the terminal relaxation time of PMA polymer chain does not vary monotonically as a function of temperature, unlike in the case of OCP; this is significant for describing viscoelastic behaviour at macroscales where satisfactory constitutive equations are not available.

Natural growth of gold dendrites within silica gels

Abstract High-grade ores in low-sulfidation epithermal precious metal deposits include banded quartz veins that contain gold dendrites. The processes by which dendrite growth takes place have been subject to debate for decades, especially given that these deposits are known to form from dilute thermal liquids that contain only trace amounts of gold. It is shown here that growth of gold dendrites in epithermal veins at the McLaughlin deposit in California (western USA) originally took place within bands of gel-like noncrystalline silica. The gel provided a framework for the delicate dendrites to form. The high permeability of the gel allowed the diffusion and advection of gold from the thermal liquids flowing across the top of the silica layers to the sites of crystal growth within the gel. Over time, the gel hardened to form opal-AG. This silica phase is thermodynamically unstable and recrystallized to quartz that has a distinct mosaic texture.

Study on Single-molecule Biophysics and Biochemistry in Dilute Liquids and Live Cells without Immobilization or Significant Hydrodynamic Flow: The Thermodynamic Single-molecule Demon.

Since mathematics provides a way to answer questions about the thermodynamic jitter in a clear, rational manner, with evidence to support it, mathematics is the reliable method necessary to get the best information on the movement of a single molecule / a single particle at the molecular scale in dilute liquids and live cells without immobilization or hydrodynamic flow. The Brownian movement (normal diffusive systems) and generally the thermodynamic jitter (anomalous diffusive systems) are ultimately the direct or indirect cause of every measurement signal at the molecular scale in diffraction limited and unlimited optical systems in dilute liquids and live cells without immobilization or hydrodynamic flow. For example, emitted photons are the epiphenomenon of the underlying process of thermodynamic jitter of single molecules / single particles at the molecular scale. The key question is: How far apart do two molecules / two particles have to be in the time domain so that the required degree of separation between the two individual molecules / the two individual particles can be quantified at the molecular scale in order to distinguish them as separate entities without immobilization or hydrodynamic flow? The Földes-Papp's limits of the singlemolecule time resolution in dilute liquids and live cells without immobilization or hydrodynamic flow are the exact answers. The diffusive process is complicated and not minimalist. A minimalist model has a third possibility, it may be right but irrelevant.

Chemical hydrolysis of hemicellulose from sugarcane bagasse. A comparison between the classical sulfuric acid method with the acidic ionic liquid 1-ethyl-3-methylimidazolium hydrogen sulfate

Dilute sulfuric acid and acidic ionic liquids are pretreatment methods used to selectively hydrolyze hemicellulose from lignocellulosic biomasses. In this work, a comparison between these techniques is carried out by treating sugarcane bagasse both with 1-ethyl-3-methylimidazolium hydrogen sulfate at different ionic-liquid and water contents and with H 2 SO 4 at the same conditions and equivalent ionic liquid molar contents. Results from the use of ionic liquid showed that it was possible to tune the biomass treatment either to achieve high hemicellulose hydrolysis yields of 72.5 mol% to very low furan and glucose co-production, or to obtain furfural at moderate yields of 18.7 mol% under conditions of low water concentration. In comparison to the use of ionic liquid, sulfuric acid pretreatment increased hemicellulose hydrolysis yields by 17%, but the 8.6 mol% furfural yield was also higher, and these yields were obtained at high water concentration conditions. Besides, no such tuning ability of the biomass treatment conditions can be made.

Numerical implementation and error analysis of nonlinear coupled fractional viscoelastic fluid model with variable heat flux

The studies conducted in the recent past reveals that the non-Newtonian are extensively applied in several engineering applications. The atypical Oldroyd-B fluid, a specific sub-category of non-Newtonian fluids, with fractional derivative constitutive equations, is very expedient to determine the approximation of many dilute polymer liquids. Since very few studies regarding the numerical solution of the aforesaid model are conducted, so the literature that can be referred to in this regard is scarce. The current article investigates the unsteady magneto-hydrodynamic flow of irregular Oldroyd-B fluid with a modified thermal flux restricted between two infinite parallel plates. Here, it is assumed that the thermal conductivity of the fluid is variable, and the impact of body forces like gravity is accordingly analyzed in terms of non-linear convection. The linear acceleration of the lower permeable plate in its plane prompts the flow. Further, we have investigated the heat transfer in the flow field through a modified fractional thermal gradient and internal heat source. The temperature gradient accelerates with time and exists among the flow boundaries. In order to determine the approximate solution unified with finite difference approximation for Caputo fractional time derivatives, we have utilized the standard Galerkin finite element method. Moreover, we have conducted a convergence analysis of the suggested numerical scheme and offered some valid error approximations. In the non-integer viscoelastic model, the local number and coefficient of skin friction are also deliberated. We have also performed some upright numerical simulations to highlight the ascendency of characteristic flow parameters of velocity and temperature fields in the proposed scheme. Here, we have analyzed that the resistive force increases by 40%, corresponding to an increment in α ranging from 0 to 0.4. Further, the heat transfer rate is diminish by 10.94% against an increase in variable thermal conductivity while it is enhanced by 37.78% corresponding to increased in Pr.

Modelling of low-frequency acoustic wave propagation in dilute gas-bubbly liquids

A numerical modelling method for the low-frequency (∼102 Hz) acoustic wave propagation in a bubbly fluid with a low gas fraction is developed in this paper. Based on the digital image analysis of the bubbly fluid, the geometrical model of polydisperse bubble populations is created. The developed method is first verified by the Wood's (1955) equation and the Commander & Prosperetti (1989) model. Then the influence of gas fraction, excitation frequency and bubble radius on the acoustic properties of the bubbly fluid is systematically examined. The obtained results confirmed that the velocities and attenuations for different bubble radius distributions are close to those obtained for the monodisperse models. The gas fraction is the key controlling factor of the acoustic velocity, while the influence of the bubble size at low frequencies can be neglected. The velocity dispersion with frequency is about 5% even in Wood's regime and the attenuation increases with a higher gas fraction and excitation frequency, while it decreases with a smaller bubble radius. By estimation of bubble expansion during the migration of gas kick, variation trends of acoustic velocity and attenuation along the wellbore are discussed. This implies that variations of the velocity and attenuation of drilling fluid at low-frequencies during the gas migration can be used for an accurate and earlier gas kick detection than currently used methods.

Mass Transfer Behavior of a Rotating Hexagonal Cylinder Reactor Suitable for Water Pollution Control

AbstractRates of mass transfer at a rotating cylinder of the hexagonal cross section were measured by the limiting current method. A drag‐reducing polymer diminished the speed of mass transfer depending on polymer quantity and rotation speediness. Rotating hexagonal cylinders provided higher degrees of mass transfer than circular rotating cylinders under identical conditions. The performance of rotating hexagonal cylinders in eliminating Cu2+ from dilute liquids was examined and found to be satisfactory. Besides the diffusion‐controlled electrochemical reactions like anodic oxidation of organic contaminants, the reactor can remove organic pollutants via catalytic diffusion‐controlled reactions. The high degree of heat transfer from the cylinder to the liquid would prevent possible hot spots, catalyst deactivation, and decomposition of products.

Influence of magnetic field on boiling heat transfer coefficient of a magnetic nanofluid consisting of cobalt oxide and deionized water in nucleate regime: An experimental study

In this paper, the analysis of the boiling process is studied in a nucleate regime on a copper surface through using oxide nanoparticles of cobalt (Co3O4) in deionized water at volume fractions of 0.005, 0.01, 0.05, 0.1, and 0.2% by means of a nucleate boiling device. The nanoparticles’ average size is about 45 nm for cobalt oxide. As the nanofluid concentration increases, the deposition and the boiling surface heat resistance increases, the nucleation points and coefficient of the boiling heat transfer decrease due to deposition. Despite the magnetic field positive effect on dilute liquids, sediment has a more negative effect than the magnetic field on concentrated nanofluids. The results reveal the improvement of the heat transfer coefficient of pool boiling under a magnetic field for low volume fractions. Maximum heat transfer of Co3O4/ DI-water is 58% compared to the DI-water observed at the concentration of 0.005%. This nanofluid can be applied to increase the heat transfer rate at low concentrations.

Tagged-particle dynamics in confined colloidal liquids

We present numerical results for the tagged-particle dynamics by solving the mode-coupling theory in confined geometry for colloidal liquids (cMCT). We show that neither the microscopic dynamics nor the type of intermediate scattering function qualitatively changes the asymptotic dynamics in vicinity of the glass transition. In particular, we find similar characteristics of confinement in the low-frequency susceptibility spectrum which we interpret as footprints of parallel relaxation. We derive predictions for the localization length and the scaling of the diffusion coefficient in the supercooled regime and discover a pronounced nonmonotonic dependence on the confinement length. For dilute liquids in the hydrodynamic limit we calculate an analytical expression for the intermediate scattering functions, which is in perfect agreement with event-driven Brownian dynamics simulations. From this, we derive an expression for persistent anticorrelations in the velocity autocorrelation function (VACF) for confined motion. Using numerical results of the cMCT equations for the VACF we also identify a crossover between different scalings corresponding to a transition from unconfined to confined behavior.

Cellulose hydrolysis using ionic liquids and inorganic acids under dilute conditions: morphological comparison of nanocellulose.

The preparation of cellulose nanocrystals (CNCs) from cellulose extracted from cotton gin motes (CGM) using an ionic liquid (1-butyl-3-methylimidazolium chloride, [BMIm]Cl) under dilute conditions is reported. The concurrent process involves minimal swelling of cellulose with an ionic liquid and hydrolysis of the cellulose initiated by the addition of either phosphoric (H3PO4), hydrochloric (HCl), or sulfuric (H2SO4) acid. The obtained nanocrystals had similar physical properties (e.g. crystallinity) to the counterparts prepared under conventional conditions and exhibited superior thermal properties for sulfate CNCs. Additionally, the obtained CNCs had low surface functionalization, yet were colloidally stable for >90 days, which is a desirable trait for post-functionalization of CNCs. This process represents a general strategy utilizing dilute ionic liquids in the preparation of nanocellulose under mildly acidic conditions.

Spatiotemporal linear stability of viscoelastic free shear flows: Dilute regime

We report the temporal and spatiotemporal stability analyses of antisymmetric, free shear, viscoelastic flows obeying the Oldroyd-B constitutive equation in the limit of low to moderate Reynolds number (Re) and Weissenberg number (We). The resulting fourth-order Orr-Sommerfeld equation is reduced to a set of six auxiliary equations that are numerically integrated starting from the rescaled far-field conditions, i.e., via Compound Matrix Method. The temporal stability analysis indicates that with increasing We, (a) the entire range of the most unstable mode is shifted toward longer waves (i.e., the entire region of temporal instability is gradually concentrated near zero wavenumber), (b) the vorticity structure contours are dilated, and (c) the residual Reynolds stresses are diminished. All these analogous observations previously reported in the inertial limit [J. Azaiez and G. M. Homsy, “Linear stability of free shear flow of viscoelastic liquids,” J. Fluid Mech. 268, 37–69 (1994).] suggest a viscoelastic destabilization mechanism operating at low and moderate Re. The Briggs idea of analytic continuation is deployed to classify regions of temporal stability, absolute and convective instabilities, as well as evanescent modes. The main result is that the free shear flow of dilute polymeric liquids is either (absolutely/convectively) unstable for all Re or the transition to instability occurs at comparatively low Re, a finding attributed to the fact that viscoelasticity aggravates instabilities via shear-induced anisotropy and the slow relaxation effects.

Blocking and remanence properties of weakly and highly interactive cobalt ferrite based nanoparticles

We compare both magnetic blocking properties and remanence curves for dilute ferrofluid and powder samples of ferrite magnetic nanoparticles. Low field DC magnetization, AC susceptibility, isothermal remanent magnetization and DC demagnetization techniques are employed to investigate the role of interparticle magnetic interactions on the superparamagnetic relaxation, the magnetic anisotropy and on the super-spin-glass state in closely packed particles. The samples used herein are 3 nm sized spinel-type nanocrystals made of a cobalt ferrite core covered by a layer of maghemite on its outermost surface and can be obtained as aqueous colloidal dispersions thanks to this core-shell strategy. They show large anisotropy attributed to an enhanced surface contribution and the blocking temperature is shifted towards higher values as interparticle distance decreases. For all investigated diluted liquids and powder samples the frequency dependency of the peak temperature is well accounted by a Vogel–Fulcher law, with the insertion of a phenomenological temperature associated to the magnitude of interparticle dipolar interactions. The fractional change of the peak temperature per decade of frequency enlights the presence of interactions between particles in dilute liquids and of a spin-glass-like state in powder samples. The remanence curves always show global demagnetizing behavior, attributed to the combination of both spin surface disorder and interparticle dipolar interactions, the former being predominant in isolated nanoparticles and the latter in powder samples. However, in the most compacted powder, exchange interaction between surface ions of different particles becomes more pronounced and promotes an additive magnetizing effect.

Plasmonic aerosols

Plasmonic nanoparticles resonantly couple to and confine light below the diffraction limit. This mechanism has enabled a modern renaissance in optical materials, with potential applications ranging from sensing and circuitry to renewable energies and medicines. However, these plasmonic materials are typically constrained to dilute liquids or solid two-dimensional surfaces, thereby limiting their possibilities. Here, we experimentally demonstrate a plasmonic aerosol by transitioning liquid suspensions of gold nanorods into the gas phase and simultaneously measuring their optical spectra. By measuring and modeling the evolution of the longitudinal absorbance peak of the nanorods from the liquid to the gas phase, we find that the aerosols are optically homogeneous and thermodynamically stable. We show that by tailoring the aspect ratio of the nanorods, the aerosol absorbance peak is tunable from visible to midwave infrared wavelengths. We find the sensitivity of the absorbance peak wavelength to changes in the refractive index of the gas depends linearly on the aspect ratio and can be estimated from the geometric and material properties of the nanorod. For high aspect ratio nanorods the sensitivity becomes extremely large, which may be useful in aiding geoengineering challenges. This work establishes plasmonic aerosols, potentially enabling exciting opportunities for fundamental and applied research.

Universality in ultradilute liquid Bose-Bose mixtures

We have studied dilute Bose-Bose mixtures of atoms with attractive interspecies and repulsive intraspecies interactions using quantum Monte Carlo methods at $T=0$. Using a number of models for interactions, we determine the range of validity of the universal equation of state of the symmetric liquid mixture as a function of two parameters: the $s$-wave scattering length and the effective range of the interaction potential. It is shown that the Lee-Huang-Yang correction is sufficient only for extremely dilute liquids with the additional restriction that the range of the potential is small enough. Based on the quantum Monte Carlo equation of state we develop a new density functional which goes beyond the Lee-Huang-Yang term and use it together with local density approximation to determine density profiles of realistic self-bound drops.

Finite Element Method for Two-Dimensional Unsteady MHD Couette Flow of a Generalized Oldroyd-B Fluid

In recent years, non-Newtonian fluids have been widely applied in engineering and industry. Due to the complexity of these fluids, there are several constitutive equations of non- Newtonian fluids. One particular subclass of non-Newtonian fluids is the class of a generalized Oldroyd-B fluids with fractional derivative constitutive equations, which has been found to approximate the response of many dilute polymeric liquids. Although the analytic solution of these equations can be derived, it contains a multi-level sum of an infinite series and Fox H-functions, which is extremely complex and difficult to evaluate. Therefore, seeking the numerical solution of the equation is of great importance. Different from the general time fractional diffusion equation, the constitutive equation is a novel multi-term time fractional diffusion equation and has a special time fractional operator on the spatial derivative, which is challenging to approximate. In this paper, we will consider the finite element method for the two-dimensional multi-term time fractional diffusion equation. Firstly, we utilise the L1 and L2 schemes to approximate the two different time fractional derivatives, respectively. Secondly, we apply the finite element method to the equation and establish the fully variational formulation. Then we adopt linear polynomials on triangular elements to derive the matrix form of the numerical scheme. Furthermore, we present the stability and convergence of the scheme. Finally, two numerical examples are investigated to show the effectiveness of our method, in which a two-dimensional unsteady MHD Couette flow of a generalized Oldroyd-B fluid is considered.

Influence of different concentrations of ionic solutions on coal spontaneous combustion

ABSTRACTConsidering the high cost of ionic liquids, this paper proposed to dilute ionic liquids with purified water to suppress coal spontaneous combustion based on an in-depth study on the mechanism of ionic liquids for suppressing coal spontaneous combustion. Three kinds of ionic liquids, namely, [HOEMIm][BF4] (HOE), [BMIm][BF4] (BM), and [AMIm]Cl (AM), were mixed with purified water to form ionic solutions with different concentrations. The differences in gas products of raw coal and samples treated with ionic solutions were comparatively analyzed, and then their mechanism of inhibiting coal spontaneous combustion was studied by calculating inhibition rates and apparent activation energy of samples. Furthermore, the molecular structure of coal was further studied by means of Fourier transform infrared spectroscopy. The results show that ionic solutions can not only absorb heat through water evaporation, but also reduce the alkyl chain content of coal by inerting hydrogen bonds in coal. Among the three kinds of ionic solutions with different concentrations, AM with a mass ratio of 1:10 achieves the best inhibitory effect.

Direct Measurement of the Differential Capacitance of Solvent-Free and Dilute Ionic Liquids

Differential capacitance is a key quantity in the understanding of electrical double-layer charging of electrolytes. However, experimental observations of ionic liquid systems are controversial, inconsistent, and often unable of confirming or refuting existing theories as well as highlighting discrepancies between the measurement techniques. We study the differential capacitance in both pure and dilute ionic liquids at room temperature. Using chronoamperometry to measure the differential capacitance of the liquids at a polycrystalline platinum electrode, we find good agreement between the measured capacitance curves and the extended mean-field model of Goodwin–Kornyshev [Goodwin, Z. A.; et al. Electrochim. Acta.2017, 225, 190–197]. A crossover is found from the pure to the dilute regime, as shown by a transition from a camel-shape capacitance curve to a U-like one, together with a nonmonotonic dependence of capacitance with electrolyte concentration.

From Solvent-Free to Dilute Electrolytes: Essential Components for a Continuum Theory.

The increasing number of experimental observations on highly concentrated electrolytes and ionic liquids show qualitative features that are distinct from dilute or moderately concentrated electrolytes, such as self-assembly, multiple-time relaxation, and underscreening, which all impact the emergence of fluid/solid interfaces, and the transport in these systems. Because these phenomena are not captured by existing mean-field models of electrolytes, there is a paramount need for a continuum framework for highly concentrated electrolytes and ionic liquid mixtures. In this work, we present a self-consistent spatiotemporal framework for a ternary composition that comprises ions and solvent employing a free energy that consists of short- and long-range interactions, along with an energy dissipation mechanism obtained by Onsager's relations. We show that the model can describe multiple bulk and interfacial morphologies at steady-state. Thus, the dynamic processes in the emergence of distinct morphologies become equally as important as the interactions that are specified by the free energy. The model equations not only provide insights into transport mechanisms beyond the Stokes-Einstein-Smoluchowski relations but also enable qualitative recovery of three distinct regions in the full range of the nonmonotonic electrical screening length that has been recently observed in experiments in which organic solvent is used to dilute ionic liquids.

Numerical methods and analysis for simulating the flow of a generalized Oldroyd-B fluid between two infinite parallel rigid plates

In recent years, non-Newtonian fluids have been widely applied in a number of engineering applications. One particular subclass of non-Newtonian fluids is the generalized Oldroyd-B fluids with fractional derivative constitutive equations, which can be used to approximate the response of many dilute polymeric liquids. Different to the general time fractional diffusion equation, the constitutive equation not only has a multi-term time derivative but also possesses a special time fractional operator on the spatial derivative, which is challenging to approximate. The literature reported on the numerical solution of this model is extremely sparse. In this paper, we will consider the finite difference method for its discretisation and propose a new scheme to approximate the time fractional derivative. Then we derive an implicit finite difference scheme and establish some new theoretical analysis of the stability and convergence. Furthermore, we present a numerical scheme to improve the time order. Finally, we present two numerical examples to show the effectiveness of our method and apply it to solve the generalized Oldroyd-B fluid model.

Near-Wall Molecular Ordering of Dilute Ionic Liquids.

The interfacial behavior of ionic liquids promises tunable lubrication as well as playing an integral role in ion diffusion for electron transfer. Diluting the ionic liquids optimizes bulk parameters, such as electric conductivity, and one would expect dilution to disrupt the near-wall molecular ordering. We study this ordering in the ionic liquids [Emim]+[NTf2]−, [Emim]+[DCA]−, and [C4mpyr]+[NTf2]−, diluted in the solvent dimethyl sulfoxide. We found a structural crossover from well-ordered ionic liquids to a well-ordered solvent with increasing dilution, but this occurs nonlinearly, with solvent molecules initially space-filling and solvating and later disrupting the ionic layers. This is of key importance for ionic liquids as optimized tunable nanolubricants.