Terms Of Surface Tension Research Articles

Rippling of polymer nanofibers

This paper studies the evolution mechanism of surface rippling in polymer nanofibers under axial stretching. This rippling phenomenon has been detected in as-electrospun polyacrylonitrile in recent single-fiber tension tests, and in electrospun polyimide nanofibers after imidization. We herein propose a one-dimensional nonlinear elastic model that takes into account the combined effect of surface tension and nonlinear elasticity during the rippling initiation and its evolution in compliant polymer nanofibers. The polymer nanofiber is modeled as an incompressible, isotropically hyperelastic Mooney-Rivlin solid. The fiber geometry prior to rippling is considered as a long circular cylinder. The governing equation of surface rippling is established through linear perturbation of the static equilibrium state of the nanofiber subjected to finite axial prestretching. The critical stretch and ripple wavelength are determined in terms of surface tension, elastic property, and fiber radius. Numerical examples are demonstrated to examine these dependencies. In addition, a critical fiber radius is determined, below which the polymer nanofibers are intrinsically unstable. The present model, therefore, is capable of predicting the rippling condition in compliant nanofibers, and can be further used as a continuum mechanics approach for the study of surface instability and nonlinear wave propagation in compliant fibers and wires at the nanoscale.

Axisymmetric bubble collapse in a quiescent liquid pool. I. Theory and numerical simulations

In this paper we analyze the final instants of axisymmetric bubble pinch-off in a low viscosity liquid. We find that both the time evolution of the bubble dimensionless minimum radius, R0(t), and of the dimensionless local axial curvature at the minimum radius, 2r1(t), are governed by a pair of two-dimensional Rayleigh-like equations in which surface tension, viscosity, and gas pressure terms need to be retained for consistency. The integration of the above-mentioned system of equations is shown to be in remarkable agreement with numerical simulations and experiments. An analytical criterion, which determines the necessary conditions for the formation of the previously reported tiny satellite bubbles, is also derived. Additionally, an estimation of the maximum velocity reached by the high speed Worthington jets ejected after bubble pinch-off, in the case axisymmetry is preserved down to the formation of the satellite bubble, is also provided.

Synthesis and characterization of imidazolinium surfactants derived from tallow fatty acids and diethylenetriamine

AbstractThis paper describes the synthesis of long‐chain dialkylamido imidazolines based on tallow fatty acids and diethylenetriamine, followed by their quaternization. Imidazolines were obtained by non‐solvent microwave synthesis using calcium oxide as support, which were then quaternized by using dimethyl sulfate as a quaternizing agent and iso‐propanol as a solvent, to produce cationic imidazolinium salts. The synthesized cationic imidazoline surfactants were evaluated for yield and cationic content. The instrumental techniques, viz. FT‐IR and 1H‐NMR, verified the formation of imidazolines and their subsequent quaternization. The surface‐active and performance properties of the cationic imidazolines in terms of critical micelle concentration, surface tension, dispersibility, emulsion stability, softening, rewettability and antistatic properties were also reported.

On the role of surface tensions and process conditions in detachment nanolithography

We report on the role of intrinsic (adhesion force and wettability) and extrinsic (temperature and pressure) conditions to fabricate dense nanoscale patterns in detachment nanolithography. A phase diagram is constructed by using a rigiflex polymeric mold, an organic film, and silicon or gold substrate. Operating conditions in terms of surface tensions and processing parameters are discussed along with comparison of the minimum resolution with a simple theory.

Study on Physicochemical Properties of Ionic Liquids Based on Alanine [Cnmim][Ala] (n = 2,3,4,5,6)

According to Fukumoto's method, a new series of ionic liquids (ILs) based on alanine, [Cnmim][Ala] ( n=2,3,4,5,6), which comprise 1-alkyl-3-methylimidazolium cation ([Cnmim](+)) and alanine anions ([Ala] (-)), were prepared and characterized. In terms of standard addition method, the density and surface tension of amino acid ILs [Cnmim][Ala] (1-alkyl-3-methylimidazolium alpha-aminopropionic acid salt) were measured in the temperature range 293.15-343.15+/-0.05 K. The volume and surface properties of the ILs [Cnmim][Ala] were discussed. A new method of determining parachor of ionic compound was proposed and was applied to estimate the physicochemical properties of amino acid ionic liquids (AAILs): molecular volume, surface tension, molar enthalpy of vaporization, and thermal expansion coefficient. In comparison with Deetlefs's method of using neutral parachor contribution, the method proposed in this work makes smaller error in estimating properties of AAILs.

A Universal Approach to Solvation Modeling

Continuum mean-field models that have been carefully designed to address the various electrostatic and nonelectrostatic interactions that develop between a molecule and a surrounding medium are particularly efficient tools for studying the effects of condensed phases on molecular structure, energetics, properties, spectra, interaction potentials, and dynamics. The SM8 model may be combined with density functional theory or Hartree-Fock theory to describe a solute's electronic structure and its self-consistent-field polarization by a solvent. A key feature is the use of class IV charge models to obtain accurate charge distributions (either in the vapor phase or in solution), even when using small basis sets that are affordable for large systems. A second key feature is that nonelectrostatic effects due to cavity formation, dispersion interactions, and changes in solvent structure are included in terms of empirical atomic surface tensions that depend on geometry but do not require atom-type assignments by the user. Use of an analytic surface area algorithm provides very stable energy gradients that allow geometry optimization in solution. The SM8 continuum model, the culmination of a series of SMx models (x = 1-8), permits the modeling of such diverse media as aqueous and organic solvents, soils, lipid bilayers, and air-water interfaces. In addition to predicting accurate transfer free energies between gaseous and condensed phases or between two different condensed phases, SMx models have been useful for predicting the significant influence of condensed phases on processes associated with a change in molecular charge, including acid/base equilibria and oxidation/reduction processes. In this Account, we provide an overview of the algorithms associated with the computation of free energies of solvation in the SM8 model. We also compare the accuracies of the SM8 model with those of other continuum solvation models. Finally, we highlight applications of the SM8 models to compute ionic solvation free energies, oxidation and reduction potentials, and pK(a) values.

Hygroscopic growth and activation of HULIS particles: experimental data and a new iterative parameterization scheme for complex aerosol particles

Abstract. The hygroscopic growth and activation of two HULIS (HUmic LIke Substance) and one Aerosol-Water-Extract sample, prepared from urban-type aerosol, were investigated. All samples were extracted from filters, redissolved in water and atomized for the investigations presented here. The hygroscopic growth measurements were done using LACIS (Leipzig Aerosol Cloud Interaction Simulator) together with a HH-TDMA (High Humidity Tandem Differential Mobility Analyzer). Hygroscopic growth was determined for relative humidities (RHs) up to 99.75%. The critical diameters for activation were measured for supersaturations between 0.2 and 1%. All three samples showed a similar hygroscopic growth behavior, and the two HULIS samples also were similar in their activation behavior, while the Aerosol-Water-Extract turned out to be more CCN active than the HULIS samples. The experimental data was used to derive parameterizations for the hygroscopic growth and activation of HULIS particles. The concept of ρion (Wex et al., 2007a) and the Szyszkowski-equation (Szyszkowski, 1908; Facchini, 1999) were used for parameterizing the Raoult and the Kelvin (surface tension) terms of the Köhler equation, respectively. This concept proved to be very successful for the HULIS samples in the saturation range from RHs larger than 98% up to activation. It was also shown to work well with data on HULIS taken from literature. Here, different atmospheric life-times and/or different sources for the different samples showed up in different coefficients for the parameterization. However, the parameterization did not work out well for the Aerosol-Water-Extract.

On stability condition for bifluid flows with surface tension: Application to microfluidics

Models for incompressible immiscible bifluid flows with surface tension are here considered. Since Brackbill et al. [J.U. Brackbill, D.B. Kothe, C. Zemach, A continuum method for modeling surface tension, J. Comput. Phys. 100 (1992) 335–354] introduced the Continuum Surface Force (CSF) method, many methods involved in interface tracking or capturing are based on this reference work. Particularly, the surface tension term is discretized explicitly and therefore, a stability condition is induced on the computational time step. This constraint on the time step allows the containment of the amplification of capillary waves along the interface and puts more emphasis on the terms linked with the density in the Navier–Stokes equation (i.e. unsteady and inertia terms) rather than on the viscous terms. Indeed, the viscosity does not appear, as a parameter, in this stability condition. We propose a new stability condition which takes into account all fluid characteristics (density and viscosity) and for which we present a theoretical estimation. We detail the analysis which is based on a perturbation study – with capillary wave – for which we use energy estimate on the induced perturbed velocity. We validate our analysis and algorithms with numerical simulations of microfluidic flows using a Level Set method, namely the exploration of different mixing dynamics inside microdroplets.

A Chemical Sensor That Can Detect the Frequency of Ultrasound

Herein is described a chemical sensor that can detect the frequency of ultrasound. Exposure of aqueous n-alkyl sulfate or sulfonate surfactant solutions to high-intensity ultrasound results in the formation of secondary carbon-centered radicals. The yield of these radicals reaches a maximum plateau, the magnitude of which is limited by the dynamic ability of the surfactant to accumulate at the rapidly oscillating gas/solution interface of cavitation bubbles. For this reason, the maximum plateau yield observed following sonolysis of sodium butane sulfonate solutions compared to that of sodium dodecyl sulfate solutions (i.e., CHSBSo/CHSDS) was greater than 1. Interestingly, it was found that the CHSBSo/CHSDS ratio had a linear dependence on ultrasound frequency. Since it is known from earlier studies that the CHSBSo/CHSDS ratio is independent of ultrasound intensity and of the geometry of flat plate exposure systems, a plot of the CHSBSo/CHSDS ratio against ultrasound frequency yields a calibration curve. With this calibration curve, the CHSBSo/CHSDS ratio can be used to detect the frequency of ultrasound in flat plate transducer systems. The effect can best be described in terms of the dynamic surface tension of surfactants in relation to the influence of ultrasound frequency on the lifetime of the gas/solution interface of sonochemically active cavitation bubbles.

Two-Phase Flows of Droplets in Contractions and Double Bends

Transient two-phase liquid-liquid flows of Newtonian fluid droplets in a primary Newtonian fluid with different viscosities, through constricted channels and double-bend channels, are numerically modelled and studied. The deformation and migration of various arrangements (arrays) of droplets, as they are carried by the primary phase into the low Reynolds number (Re), developing Hagen-Poiseuille laminar flow, is computed and discussed on the basis of the non-dimensional numbers: Capillary number (Ca), Reynolds number (Re), Weber number (We) and viscosity ratio (λ). The observations are well compared with the results of the literature. To predict the contours of droplets, we implement a level-set method (LSM) for capturing interfaces with high order WENO and TVD Runge-Kutta schemes. The LSM implicitly provides the conditions for the revised, nearly second-order, two-phase, time-dependent, 2-D Navier-Stokes momentum equations’ solver, incorporating viscous and surface tension terms depending on the level-set function.

Nonuniversal dynamics of dimer growing interfaces

A finite temperature version of body-centered solid-on-solid growth models involving attachment and detachment of dimers is discussed in 1+1 dimensions. The dynamic exponent of the growing interface is studied numerically via the spectrum gap of the underlying evolution operator. The finite size scaling of the latter is found to be affected by a standard surface tension term on which the growth rates depend. This nonuniversal aspect is also corroborated by the growth behavior observed in large scale simulations. By contrast, the roughening exponent remains robust over wide temperature ranges.

Continuous peeling extrusion of SEBS block copolymers

During continuous peeling, a central polymer rod free of visible defects was continuously extruded while being peeled at the die exit. Continuous peeling can occur at flow rates orders of magnitude higher than those at which initial surface cracking is observed. Thus, if continuous peeling can be controlled it may have potential industrial applications. The aim of this work was to study how different extrusion parameters (temperature, flow rate, die length and diameter) affect the presence of continuous peeling. The melt exiting the die has been filmed to link physical measurements and observations and to determine whether or not continuous peeling is present. Different criteria have been considered to represent the extrusion conditions under which continuous peeling may occur. Surface tension criteria can be used to try to predict the appearance and disappearance of continuous peeling. A correlation formula is also proposed for the rod diameter in terms of surface tension. Our results show that the ratio of the rod diameter to the die diameter is approximately 25% greater in the case of short-orifice dies ( L/ D ≈ 0) than for long capillaries ( L/ D ≈ 10). The correlations obtained allow analysis and discussion of flow regimes for possible applications.

An integrable equation governing short waves in a long-wave model

The dynamics of a nonlinear and dispersive long surface capillary-gravity wave model equation is studied analytically in its short-wave limit. We exhibit its Lax pair and some non-trivial conserved quantities. Through a change of functions, an unexpected connection between this classical surface water-wave model and the sine-Gordon (or sinh-Gordon) equation is established. Numerical and analytical studies show that in spite of integrability their solutions can develop singularities and multivaluedness in finite time. These features can be traced to the fact that the surface tension term in the energy involves second-order derivatives. It would be interesting to see in an experiment whether such singularities actually appear, for which surface tension would be specifically responsible.

Level-Set method and stability condition for curvature-driven flows

We consider models for the simulation of curvature-driven incompressible bifluid flows, where the surface tension term is discretized explicitly. From this formulation a numerical stability condition arises for which we present a new theoretical estimation for low and medium Reynolds numbers. We illustrate our analysis with numerical simulations of microfluidic flows using Level-Set method. Finally, we propose a method to reduce computational cost induced by this stability condition for low flow velocities. To cite this article: C. Galusinski, P. Vigneaux, C. R. Acad. Sci. Paris, Ser. I 344 (2007).

Structure and dynamics of thin polymer films using synchrotron X-ray scattering

Recent measurements of the scattering function and of the dynamics of surface and interfacial fluctuations in thin supported molten films and bilayers using synchrotron X-ray diffuse scattering and photon correlation spectroscopy in reflection geometry are reported. The results for monolayer films thicker than four times of the radius of gyration of polystyrene show behavior of normal over-damped capillary waves expected for the surface fluctuations of a viscous liquid. However, thinner films show deviations indicating the need to account for viscoelasticity. The theory has been extended to the surface and interfacial modes in a bilayer film system. The results are discussed in terms of surface tension, viscosity and shear modulus. Also recent experiments to measure the isothermal compressibility of supported polystyrene films by studying `bulk' scattering from the interior of the films is discussed.

Lattice Boltzmann model for simulating immiscible two-phase flows

The lattice Boltzmann equation is often promoted as a numerical simulation tool that is particularly suitable for predicting the flow of complex fluids. This paper develops a two-dimensional 9-velocity (D2Q9) lattice Boltzmann model for immiscible binary fluids with variable viscosities and density ratio using a single relaxation time for each fluid. In the macroscopic limit, this model is shown to recover the Navier–Stokes equations for two-phase flows. This is achieved by constructing a two-phase component of the collision operator that induces the appropriate surface tension term in the macroscopic equations. A theoretical expression for surface tension is determined. The validity of this analysis is confirmed by comparing numerical and theoretical predictions of surface tension as a function of density. The model is also shown to predict Laplace's law for surface tension and Poiseuille flow of layered immiscible binary fluids. The spinodal decomposition of two fluids of equal density but different viscosity is then studied. At equilibrium, the system comprises one large low viscosity bubble enclosed by the more viscous fluid in agreement with theoretical arguments of Renardy and Joseph (1993 Fundamentals of Two-Fluid Dynamics (New York: Springer)). Two other simulations, namely the non-equilibrium rod rest and the coalescence of two bubbles, are performed to show that this model can be used to simulate two fluids with a large density ratio.

Low-pressure plasma pretreatment of polyphenylene sulfide (PPS) surfaces for adhesive bonding

Polyphenylene sulfide (PPS) is a high-performance plastic with outstanding mechanical, physical and thermal characteristics for lightweight automobiles and rail-mounted vehicles. The adhesive behavior of PPS with aluminum plates by using epoxy (EP) and polyurethane (PU) adhesives is the subject of these investigations, whereby the activation of the PPS surfaces took place by means of low-pressure plasma treatment. The determination of the changes caused in terms of topography, surface tension and chemical composition of the PPS surfaces after low-pressure plasma treatment was carried out by means of scanning electron microscopy (SEM), contact angle measurements and energy dispersive X-ray analysis (EDX). The adhesion bond strength increased after oxygen plasma treatment by 103% (EP 1), 134% (EP 2) and 56% (PU). After argon plasma treatment, the increase in adhesive bond strength was only 79% (EP 1), 122% (EP 2) and 27% (PU). The failure took place with increasing adhesive strength with EP 1 predominantly cohesively in the PPS at the aluminum lap end, with EP 2 adhesively at the aluminum surface and with PU cohesively in the adhesive layer. The surface energy and the polar contributions increased significantly with treatment time with both plasma gases. This was more pronounced with oxygen than with argon plasma. The dispersive contributions to the surface free energy hardly changed with increasing treatment time. The SEM shows that the surface roughness also increases with treatment time in the case of the oxygen plasma more compared with the argon plasma. Furthermore, a deposit of reaction products on the surfaces was detected.

A Simple Weighted Integration Method for Calculating Surface Tension Force to Suppress Parasitic Flow in the Level Set Approach

Parasitic flows may occur in the numerical simulation of incompressible multiphase flow due to errors in the calculation of surface tension terms, specifically for the curvature and unit normal vector. An improved method for calculating the surface tension based on the level set approach is proposed, in which the contribution of not only the center node but also the rest area of a control volume to the calculation of surface tension is considered in a balanced manner. The weighted integration method (WIM) is more consistent with the concept of a banded interface in the level set method. It is applied to the temporal evolution of a two-dimensional neutrally buoyant liquid drop and a buoyancy driven deformable bubble in an immiscible fluid for the validation of WIM. The results show that the parasitic flows are evidently suppressed by the weighted integration method. The weight factors for WIM in 3-D cases are also suggested.

Model for phase transition based on statistical disassembly of nuclei at intermediate energies

Consider a model of particles (nucleons) which has a two-body interaction which leads to bound composites with saturation properties. These properties are : all composites have the same density and the ground state energies of composites with k nucleons are given by -kW+\sigma k^{2/3} where W and \sigma are positive constants. W represents a volume term and \sigma a surface tension term. These values are taken from nuclear physics. We show that in the large N limit where N is the number of particles such an assembly in a large enclosure at finite temperature shows properties of liquid-gas phase transition. We do not use the two-body interaction but the gross properties of the composites only. We show that (a) the p-\rho isotherms show a region where pressure does not change as $\rho$ changes just as in Maxwell construction of a Van der Waals gas, (b) in this region the chemical potential does not change and (c) the model obeys the celebrated Clausius-Clapeyron relations. A scaling law for the yields of composites emerges. For a finite number of particles N (upto some thousands) the problem can be easily solved on a computer. This allows us to study finite particle number effects which modify phase transition effects. The model is calculationally simple. Monte-Carlo simulations are not needed.

Study on the Properties of Amino Acid Ionic Liquid EMIGly

In terms of standard addition method, the density and surface tension of an amino acid ionic liquid EMIGly(1-ethyl-3-methylimidazolium aminoacetate) were measured under dry argon atmosphere in the temperature range of 288.15-343.15 K. The properties of volume and surface for pure EMIGly were discussed in terms of the interstice model and Glasser's theory. The thermal expansion coefficient alpha = 5.03 x 10(-4) K(-1) calculated using interstice model is in good agreement with alpha (experimental) = 5.20 x 10(-4) K(-1).