Surface Tension Relaxation Research Articles

A study on the dilational modulus of adsorbed globular protein films – Under a near periodic area fluctuation and rapid surface perturbation

BackgroundUnderstanding how surface area (SA) fluctuation affects the dilational modulus (E) of globular protein films is crucial for evaluating their mechanical properties and practical utility. However, limited reports are available in the literature and the measurement error is unclear. MethodThe impact of SA fluctuation and large, forced perturbation on the E of bovine serum albumin (BSA) and human serum albumin (HSA) film was investigated. The E was evaluated by analyzing surface tension (ST) and SA relaxation data obtained using a pendant bubble tensiometer. Significant findingsThe data revealed that a large fluctuation in SA exerted a notable influence on the E: a distinct peak and minima in E being detected at the onset and end, respectively (at magnitude ΔA/A > ∼3 % and at oscillation frequency ƒ = 0.3 – 1.1 mHz for adsorbed BSA/HSA film). In contrast, a comparatively smaller SA fluctuation caused only a slight variation in E. Furthermore, a large, forced perturbation led to a rise in E, exhibiting a distinctly high value after a rapid bubble compression, followed by a subsequent decrease to a distinctly low E.

Effect of Surface Tension Relaxation on the Stability of a Charged Jet

Effect of Surface Tension Relaxation on the Stability of a Charged Jet

Effect of Surface Tension Relaxation on the Stability of the Charged Jet

In the asymptotic calculations of the first order of smallness by the dimensionless amplitude of capillary waves on the surface of charged jets of polar liquid, the effect of the relaxation effect of surface tension on the regularities of their implementation is investigated. Calculations are carried out on the model of an ideal non-compressible electrically conductive fluid. It has been shown that taking into account the effect of dynamic surface tension leads to an increase in the order of the dispersion equation, which has another damping root, which is obliged to destroy the near-surface double electric layer (destruction of the ordering of polar molecules in the near-surface layer), which undergoes electrostatic instability at sufficiently large charges (pre-breakdown in the sense of ignition of corona discharge in air). In the ideal fluid mathematical model used, the relaxation motion of the jet surface disturbances that occurs when the surface tension relaxation effect is turned on and the attenuation decrements of capillary wave motions are purely of a relaxation nature.

Experimental study of the effect of various surfactants on the wave characteristics of the film flow

In this paper we present the results of experimental investigation of the effect of ionic surfactants (sodium dodecyl sulfate and cetrimonium bromide) at various concentrations on the vertical film flow in the range of Reynolds numbers 10 < Re < 50. The laser-induced fluorescence technique was used for instant film thickness measurements. The results are compared with data obtained for non-ionic Triton X-100. For all surfactants the rivulets formation and the dumping of wave motion are observed. The difference in the action of ionic and non-ionic surfactants on wave motion is revealed. Such deviations indicate that for ionic surfactants the surface tension relaxation process (at least in the case of film flows) is not fully described by diffusion processes, but has a more complex nature.

The effect of in situ‐formed copolymers on the morphology of reactive poly(phenylene ether)/poly(amide‐6) blends

AbstractPoly(phenylene ether) (PPE)/poly(amide‐6) (PA6) blends are examined in light of the information provided by two‐dimensional chromatography and chemorheology. Chromatography provides a snapshot of the blend composition in the finished material, while rheology presents us with a direct insight into the reactions taking place in the melt. Block copolymer formation is chromatographically confirmed for the blends prepared with a coupling agent, but also for the blend prepared without any coupling agent. No co‐continuous morphology is observed by scanning electron microscope. Instead, a coarse structure of PPE droplets in the PA6 matrix is obtained for the blend prepared without coupling agent. This is explained by the combined effects of the low viscosity of PA6 and the inherently formed copolymers. The PPE domains are smaller in the blends prepared with the coupling agents. Their size is correlated with the copolymer formation, surface tension, and interphase relaxation time. The data evidence a complex system where reactions resulting in the formation of copolymer via coupling or grafting take place together with the extension of the PPE and condensation growth of the PA6 polymers.

Mass transport of SDS and AOT solutions during a rapid surface expansion: Relaxation of surface tension

Abstract Surface tension (ST) relaxations are influential in industrial processes that are characterized by substantial surface deformations. Despite this, the dynamics of surfactant adsorption onto a dilating surface is still unclear. Recently, the ST relaxation of a non-ionic surfactant (TX-100) was reported (Lin et al. (2017) [17]), but little is known about the behavior of ionic surfactants. In this study, the relaxations of ST and surface dilational rates (λ) of ionic aerosol-OT (AOT) and sodium dodecyl sulfate (SDS) solutions were investigated by monitoring a continuously expanding bubble using a pendant bubble tensiometer. The data showed that during the rapid bubble expansion, ST of AOT solutions increased with time, while that of SDS changed negligibly. This implied that the mass transfer rate of AOT molecules from bulk to the bubble surface during expansion (at λ

Effects of Sodium Benzoate and Sodium Chloride on the Aggregation Behaviors of PEO‐PPO‐ph‐PPO‐PEO and PPO‐PEO‐ph‐PEO‐PPO at the Air/Water Interface

AbstractThe effect of sodium benzoate and sodium chloride on the aggregation behavior of PEO‐PPO‐ph‐PPO‐PEO (BPE) and PPO‐PEO‐ph‐PEO‐PPO (BEP) polyethers at the air/water interface was investigated by measuring the equilibrium surface tension, surface dilational viscoelasticity, and surface tension relaxation. The measurements of surface tension showed that sodium benzoate has a better effect on decreasing the surface tension of BPE and BEP solutions than NaCl, especially when the polyether concentrations are low. According to dilational viscoelasticity measurements, the concentration of BPE required for the maximum dilational modulus is lower than that of BEP, indicating that BPE more easily forms a compact adsorbed layer. The dilational modulus values of BPE solutions in the presence of sodium benzoate and NaCl first increase and then decrease after passing through a maximum, and then they increase again with increasing electrolyte concentration. On the other hand, the dilational modulus values of BEP solutions in the presence of sodium benzoate and NaCl first increase to a maximum and then decrease with increasing electrolyte concentration. The surface tension relaxation results are consistent with those of dilational viscoelasticity. The different effects of sodium benzoate and NaCl on the polyether aggregation behaviors are caused by the strong hydrophobic and π‐π interactions between polyethers and sodium benzoate. This work has a great importance for the application and development of polyethers.

Comparison of Additive and Polarizable Models with Explicit Treatment of Long-Range Lennard-Jones Interactions Using Alkane Simulations.

Long-range Lennard-Jones (LJ) interactions have a significant impact on the structural and thermodynamic properties of nonpolar systems. While several methods have been introduced for the treatment of long-range LJ interactions in molecular dynamics (MD) simulations, increased accuracy and extended applicability is required for anisotropic systems such as lipid bilayers. The recently refined Lennard-Jones particle-mesh Ewald (LJ-PME) method extends the particle-mesh Ewald (PME) method to long-range LJ interactions and is suitable for use with anisotropic systems. Implementation of LJ-PME with the CHARMM36 (C36) additive and CHARMM Drude polarizable force fields improves agreement with experiment for density, isothermal compressibility, surface tension, viscosity, translational diffusion, and 13C T1 relaxation times of pure alkanes. Trends in the temperature dependence of the density and isothermal compressibility of hexadecane are also improved. While the C36 additive force field with LJ-PME remains a useful model for liquid alkanes, the Drude polarizable force field with LJ-PME is more accurate for nearly all quantities considered. LJ-PME is also preferable to the isotropic long-range correction for hexadecane because the molecular order extends to nearly 20 Å, well beyond the usual 10-12 Å cutoffs used in most simulations.

Influence of the surface limiting elasticity modulus on the impact behavior of droplets of difenoconazole-loaded mesoporous silica nanoparticles with associated SDS.

The relation between the surface limiting elasticity modulus, ε0, of difenoconazole-loaded mesoporous silica nanoparticle (DF-MSN) formulations with associated SDS and the height of the first returning droplet impacting on cabbage and rice leaf surfaces was investigated. The surface dilational rheology properties were determined by means of surface tension relaxation. The impact of a droplet on the leaf surface was recorded with a high-speed camera. The surface limiting elasticity modulus, ε0, shows differences with different SDS concentrations. A positive correlation between droplet first rebound height and the surface limiting elasticity modulus, ε0, is observed. The pesticide droplet impact on the target leaf surface is a rather complex phenomenon, so the focus of this article is to establish a relationship between the surface limiting elasticity modulus, ε0, and droplet first rebound height. These findings introduce a chemical way to affect the impact behavior of pesticide droplets on target crop leaf surfaces, which may be of particular importance for pesticide spraying and crop protection, especially for hydrophobic and superhydrophobic target crops.

Surface tension behavior of aqueous solutions of a propoxylated surfactant and interfacial tension behavior against a crude oil

Equilibrium interfacial tensions (EIFTs) are important in determining the oil recovery efficiency in surfactant-based enhanced oil recovery (EOR) processes, in which ultralow IFT values (less than 10−2mNm−1) are often needed. The dynamic IFTs (DIFTs) for un-pre-equilibrated drops in contact with aqueous solutions and the adsorption mechanisms at the oil-water interface are important for the initial stages of EOR and for screening various surfactants for field applications. The IFT behavior of a commercial anionic surfactant, termed S13D, a single-chain propoxylated sodium sulfate salt has been studied. The synthetic brine used (9700ppm total dissolved solids) was similar to that in an actual reservoir of oil, from which purified crude oil samples were prepared.The dynamic and equilibrium surface tensions (DSTs and ESTs) and the IFTs were measured at 24°C, with the emerging bubble/drop method, or the spinning bubble/drop method. The DSTs for surfactant concentrations from 0.1 to 10,000ppm by weight have a simpler adsorption mechanism than the DIFTs, involving only diffusion from the aqueous phase and adsorption/desorption. Surface and interfacial tension relaxation tests after surface area perturbation were performed for establishing the validity of the ESTs and EIFTs. The critical micelle concentration (cmc) was 12ppm in water and 1ppm in brine. The lowest observed EIFT was 1mNm−1 with water and ultralow, 2×10−3mNm−1, with brine. The equilibration timescales were shorter with brine than with water, for both DSTs and DIFTs, and slightly longer for DIFTs, because evidently the adsorbed surfactant desorbed and diffused away from the interface, for partitioning in the oil phase. The results suggest that the IFTs were associated with the typical adsorbed soluble monolayers at the oil-water interface, and that solubilization effects did not affect the measured DIFTs and EIFTs.

Low-Temperature Soft-Cover Deposition of Uniform Large-Scale Perovskite Films for High-Performance Solar Cells.

Large-scale high-quality perovskite thin films are crucial to produce high-performance perovskite solar cells. However, for perovskite films fabricated by solvent-rich processes, film uniformity can be prevented by convection during thermal evaporation of the solvent. Here, a scalable low-temperature soft-cover deposition (LT-SCD) method is presented, where the thermal convection-induced defects in perovskite films are eliminated through a strategy of surface tension relaxation. Compact, homogeneous, and convection-induced-defects-free perovskite films are obtained on an area of 12 cm2 , which enables a power conversion efficiency (PCE) of 15.5% on a solar cell with an area of 5 cm2 . This is the highest efficiency at this large cell area. A PCE of 15.3% is also obtained on a flexible perovskite solar cell deposited on the polyethylene terephthalate substrate owing to the advantage of presented low-temperature processing. Hence, the present LT-SCD technology provides a new non-spin-coating route to the deposition of large-area uniform perovskite films for both rigid and flexible perovskite devices.

Impact of surface dilation rate on dynamic surface tension

In past studies, estimating the dynamic surface tension in processes involving significant surface deformation relied heavily on empirical relations. Despite its importance, the detailed dynamics of surfactant adsorption onto a dilating surface have not been investigated extensively. In this study, we modified the pendant bubble tensiometer to provide direct observation on the dynamics of surfactant adsorption during rapid surface dilation. The relaxation of dynamic surface tension for bubbles rapidly expanding in the solution of four different bulk concentrations of Triton-X 100 was studied. It was found that surface tension rose with increasing surface area due to the decrease in surface concentration. Moreover, when surface dilational rate was increased, it was found that the relation between surface tension and surface area came to resemble the equation of state of two dimensional surfactant phase when dilational rates were larger than a certain threshold value, indicating that the adsorption of surfactant became negligible. This threshold value was found to increase with surfactant concentration. The results showed that the procedure established in this study could serve as a simple guideline to determine whether adsorption can be neglected in a process involving dilating surfaces. In addition, the detailed dynamical data reported in this work can serve as an experimental reference for multiphase flow simulations involving species that adsorb on interfaces.

Tensiometric and Phase Domain Behavior of Lung Surfactant on Mucus-like Viscoelastic Hydrogels.

Lung surfactant has been observed at all surfaces of the airway lining fluids and is an important contributor to normal lung function. In the conducting airways, the surfactant film lies atop a viscoelastic mucus gel. In this work, we report on the characterization of the tensiometric and phase domain behavior of lung surfactant at the air-liquid interface of mucus-like viscoelastic gels. Poly(acrylic acid) hydrogels were formulated to serve as a model mucus with bulk rheological properties that matched those of tracheobronchial mucus secretions. Infasurf (Calfactant), a commercially available pulmonary surfactant derived from calf lung extract, was spread onto the hydrogel surface. The surface tension lowering ability and relaxation of Infasurf films on the hydrogels was quantified and compared to Infasurf behavior on an aqueous subphase. Infasurf phase domains during surface compression were characterized by fluorescence microscopy and phase shifting interferometry. We observed that increasing the bulk viscoelastic properties of the model mucus hydrogels reduced the ability of Infasurf films to lower surface tension and inhibited film relaxation. A shift in the formation of Infasurf condensed phase domains from smaller, more spherical domains to large, agglomerated, multilayer structures was observed with increasing viscoelastic properties of the subphase. These studies demonstrate that the surface behavior of lung surfactant on viscoelastic surfaces, such as those found in the conducting airways, differs significantly from aqueous, surfactant-laden systems.

Aggregation behavior of X-shaped branched block copolymers at the air/water interface: effect of block sequence and temperature

The aggregation behaviors of X-shaped block copolymers, Tetronic 1107 and Tetronic 90R4 with a sequential and reverse architecture, at the air/water interface were studied. The effects of block sequence, concentration, and temperature were investigated by equilibrium surface tension, surface dilational viscoelasticity, and surface tension relaxation measurements. The conformations of Tetronic 1107 and Tetronic 90R4 are different at the air/water interface. The possible adsorption model of Tetronic 1107 is “brush” and that of Tetronic 90R4 is invert “umbrella”. With the increase of temperature, the dilational modulus of Tetronic 1107 solutions decreases, while that of Tetronic 90R4 solutions increases. The mechanisms of the temperature which effects on the conformational transition of Tetronic 1107 and Tetronic 90R4 were discussed in detail. Furthermore, the thermodynamic parameters for the micellization of Tetronic 1107 and Tetronic 90R4 were compared at different temperatures.

Relaxation of Surface Tension in the Liquid–Solid Interfaces of Lennard-Jones Liquids

We have established the surface tension relaxation time in the liquid-solid interfaces of Lennard-Jones (LJ) liquids by means of direct measurements in molecular dynamics (MD) simulations. The main result is that the relaxation time is found to be almost independent of the molecular structures and viscosity of the liquids (at 70-fold change) used in our study and lies in such a range that in slow hydrodynamic motion the interfaces are expected to be at equilibrium. The implications of our results for the modeling of dynamic wetting processes and interpretation of dynamic contact angle data are discussed.

Parenchymal mechanics, gas mixing, and the slope of phase III

A model of parenchymal mechanics is revisited with the objective of investigating the differences in parenchymal microstructure that underlie the differences in regional compliance that are inferred from gas-mixing studies. The stiffness of the elastic line elements that lie along the free edges of alveoli and form the boundary of the lumen of the alveolar duct is the dominant determinant of parenchymal compliance. Differences in alveolar size cause parallel shifts of the pressure-volume curve, but have little effect on compliance. However, alveolar size also affects the relation between surface tension and pressure during the breathing cycle. Thus regional differences in alveolar size generate regional differences in surface tension, and these drive Marangoni surface flows that equilibrate surface tension between neighboring acini. Surface tension relaxation introduces phase differences in regional volume oscillations and a dependence of expired gas concentration on expired volume. A particular example of different parenchymal properties in two neighboring acini is described, and gas exchange in this model is calculated. The efficiency of mixing and slope of phase III for the model agree well with published data. This model constitutes a new hypothesis concerning the origin of phase III.

Experimental investigation of charged liquid jet efflux from a capillary

The shapes and electrical characteristics of charged liquid (water, ethanol, glycerol, castor oil) jets emitted from a metal capillary have been experimentally studied depending on the applied high voltage. A map of efflux regimes in the flow velocity-applied voltage coordinates is constructed for water. The effects of medium viscosity, surface tension, and charge relaxation time on the laws of jet efflux are analyzed.

Relaxation of surface tension in the free-surface boundary layer of simple Lennard-Jones liquids

In this paper we use molecular dynamics to answer a classical question: how does the surface tension on a liquid/gas interface appear? After defining surface tension from the first principles and performing several consistency checks, we perform a dynamic experiment with a single simple liquid nanodroplet. At time zero, we remove all molecules of the interfacial layer, creating a fresh bare interface with the bulk arrangement of molecules. After that the system evolves towards equilibrium, and the expected surface tension is re-established. We found that the system relaxation consists of three distinct stages. First, the mechanical balance is quickly re-established. During this process the notion of surface tension is meaningless. In the second stage, the surface tension equilibrates, and the density profile broadens to a value which we call "intrinsic" interfacial width. During the third stage, the density profile continues to broaden due to capillary wave excitations, which does not however affect the surface tension. We have observed this scenario for monatomic Lennard-Jones (LJ) liquid as well as for binary LJ mixtures at different temperatures, monitoring a wide range of physical observables.

Interfacial layers from the protein HFBII hydrophobin: Dynamic surface tension, dilatational elasticity and relaxation times

The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (<11mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at the higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by adsorption of such proteins.

Effect of Alcohols on Aggregation Behaviors of Branched Block Polyether Tetronic 1107 at an Air/Liquid Surface

The aggregation behaviors of branched block polyether Tetronic 1107 (T1107) at an air/liquid surface was investigated in mixed solvents consisting of water and one of the following polar cosolvents: ethanol, n-propanol, ethylene glycol (EG), or glycerol (GLY). Surface tension measurements provide information about the effects of cosolvents on the critical micellization concentration (cmc), the standard Gibbs energy (ΔG°(mic)), the maximum surface excess concentration (Γ(max)), the minimum area per polyether molecule at the air/liquid surface (A(min)), and the standard free energy of adsorption (ΔG°(ads)). The addition of ethanol and n-propanol to water disfavors the micellization and progressively increases the cmc of T1107, whereas the cmc decreases with the addition of EG and GLY. The values of ΔG°(mic) of T1107 are all negative in mixed solvents, and their absolute values become smaller as the ethanol or n-propanol content increases but become larger as the EG or GLY content increases. The cosolvents have a significant effect on the surface adsorption and cmc, and the order is as follows: n-propanol-water > ethanol-water > water > EG-water > GLY-water. The octanol/water partition coefficient (log P) of the cosolvent is used to correlate the effects, and it could capture the effect of cosolvents on the cmc qualitatively. The surface dilational rheological properties of T1107 in water and water-alcohol mixtures were also studied by surface dilational viscoelasticity and surface tension relaxation measurements. The dilational elasticity decreases monotonously in the presence of ethanol or n-propanol. With the increasing concentration of EG and GLY, the dilational elasticity of T1107 passes through a maximum that coincides with the change in Γ(max).