Dilational Viscoelasticity Research Articles

Experimental study on the performance of foamy oil flow under different solution gas–oil ratios

The lower limit of solution gas–oil ratio for foamy oil from Carabobo reservoir was determined by sandpack and visualization experiments, and explained by interfacial tension, interfacial dilational viscoelasticity, oil viscosity and elastic energy.

Effect of starch particles on foam stability and dilational viscoelasticity of aqueous-foam

Surface dilational rheological behavior and foam stability of starch/surfactant mixed solutions were studied at different starch concentrations and constant surfactant concentration. The results show that dilational viscoelasticity modulus, dilational elasticity modulus and dilational viscosity modulus increase with the concentration of starch particles. Foam stability increases with dilational viscoelasticity. Foam strength also increases with starch concentration. Starch particles play a positive effect on foam stability and dilational viscoelasticity and the effect becomes more significant as drainage proceeds. Film pictures indicate that the film with 20% (by mass) starch particles is thicker than that without starch. Starch particles gather in Plateau border and resist drainage, making the foam more stable.

Interfacial tension and surface elasticity of carbon black (CB) covered oil-water interface.

Carboxyl-terminated carbon black (CB) particles have been proposed as readily available, biocompatible dispersants to stabilize oil-in-water emulsions after an oil spill. Since the reduction in interfacial tension and the increase in interfacial elasticity are the key parameters which relate interfacial mechanics to emulsion stability, this investigation explores the effect of CB adsorption and surface coverage on oil-water interfacial tension and elasticity. Flocculation of CB was explored as ionic strength was increased from 0 to 0.6 M, approximately the salinity of seawater. As salinity increases, CB aggregates into larger particles from 100 nm to 6 μm. The interfacial tension and dilational viscoelasticity were measured for two systems: a drop of a CB suspension in oil and an inverted oil drop in a CB suspension. For the arrangement of a CB suspension drop in oil, most of the CB settles and accumulates toward the bottom of the drop with only small surface adsorption and no appreciable effect is observed on the dynamic interfacial tension or the dilational viscoelasticity. On reversing the arrangement to an inverted oil drop in CB suspension and increasing the convection of the outer phase, the surface coverage increases considerably. The CB coverage becomes more uniform with higher convection with an average value of approximately 2.6 g/m(2), which is representative of the coverage in Pickering emulsions stabilized by CB particles. The CB coverage decreases the surface tension from about 30 to 8.5 mN/m accompanied by an increase in the surface elasticity to 20.7 mN/m. The sharp contrast between the results from the CB suspension drop and the oil drop could be partially due to the effect of the wetting characteristics of the particles or due to the significant differences between the convection in the two cases.

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.

Unusual penetration of phospholipid mono- and bilayers by Quillaja bark saponin biosurfactant

The interactions between a model phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a biosurfactant Quillaja Bark Saponin (QBS) obtained from the bark of Quillaja saponaria Molina were studied using simple models of biological membranes. QBS is known to interact strongly with the latter, exerting a number of haemolytic, cytotoxic and anti-microbial actions. The interaction of QBS dissolved in the subphase with DPPC monolayers and silicon-supported bilayers was studied above the cmc (10−3M). Surface pressure relaxation and surface dilatational rheology combined with quartz crystal microbalance (QCM) and neutron reflectivity (NR) were employed for this purpose. The DPPC-penetrating abilities of QBS are compared with those of typical synthetic surfactants (SDS, CTAB and Triton X-100). We show that the penetration studies using high surface activity (bio)surfactants should be performed by a subphase exchange, not by spreading onto the surfactant solution. In contrast to the synthetic surfactants of similar surface activity, QBS does not collapse DPPC mono- and bilayers, but penetrates them, improving their surface dilatational elastic properties even in the highly compressed solid state. The dilatational viscoelasticity modulus increases from 204 mN/m for pure DPPC up to 310 mN/m for the QBS-penetrated layers, while it drops to near zero values in the case of the synthetic surfactants. The estimated maximum insertion pressure of QBS into DPPC monolayers exceeds the maximum surface pressure achievable in our setup, in agreement with the surface rheological response of the penetrated layers.

Utilization of Surfactant-Stabilized Foam for Enhanced Oil Recovery by Adding Nanoparticles

Nitrogen foam flooding is a promising technique for enhanced oil recovery, but instability of the foam limits its application. In this article, partially hydrophobic modified SiO2 nanoparticles with an anionic surfactant, sodium dodecyl sulfate (SDS), were used together to increase foam stability. Micromodel flooding and sandpack flooding were adopted to assess the stability and effect on enhanced oil recovery of the SiO2 stabilized foam (SiO2/SDS foam). The experimental data showed that the foam stability was decreased with an increase in temperature, while the foam volume was increased first and then decreased. SiO2/SDS foam showed better temperature tolerance than the SDS foam (foam stabilized by SDS) due to the adsorption of nanoparticles on the surface of the bubble. Almost all of the bubbles maintained spherical or ellipsoidal shape with prolonged time due to the enhanced surface dilational viscoelasticity, which was different from that of SDS foam. According to the micromodel flooding results, SiO2/SDS foam displaced more oil than brine flooding, SDS solution flooding, or SDS foam flooding. As the foam stability was enhanced, gas mobility and channeling were controlled effectively. In addition, more oil on the pore wall and in the dead-end pores was displaced out because of the higher viscoelasticity of the SiO2/SDS foam. The sandpack flooding results showed that the increase of differential pressure and profile control effect was a proportional function of the SiO2 concentration in SiO2/SDS foam. The test with a higher SiO2 concentration resulted in a higher oil recovery when SiO2 concentration was less than 1.5 wt %.

Interfacial activity of amino acid-based glycerol ether surfactants and their performance in stabilizing O/W cosmetic emulsions

Biocompatible and biodegradable molecules of Phenyl- and Tyrosine-glycerol ether surfactants are good candidates for eco-friendly cosmetic emulsions. Both molecules have a hydrophobic alkyl chain with 12 carbon atoms, but different amino acids in the hydrophilic head: phenylalanine (PhGE12) and tyrosine (TyrGE12). This study reports on the activity of liquid/liquid interfaces with the glycerol ether surfactants being dissolved in the organic phase (olive oil) and the aqueous phase containing the non-ionic poly(oxyethelene) (20) sorbitan monooleate (trade name Tween 80). Measurements refer to a) dynamic surface tension by drop profile tensiometry and drop volume tensiometry and b) interfacial dilatational viscoelasticity by oscillating drop profile analysis. It is shown that PhGE12 attains much lower interfacial tension values and exhibits faster interfacial adsorption than TyrGE12 whereas interfacial dilatational viscoelasticity values are comparable between the two surfactants. Oil-in-water emulsions are prepared and their stability is assessed by monitoring the time evolution of creaming index. To interpret observations, measurements of the emulsions’ initial droplet size distributions and apparent bulk viscosity are employed. It is found that at similar surfactant concentrations, PhGE12 emulsions exhibit better stability than TyrGE12 emulsions. This might be attributed to the lower interfacial tension in PhGE12 emulsions that yield droplet size distributions richer in intermediate (∼50μm) and small size (∼0.5μm) droplets and to their higher apparent viscosities. On the other hand, increasing the concentration of either surfactant leads to a substantial increase of emulsions stability which is in line with the lower interfacial tension and higher apparent viscosity measurements but does not agree with the insensitive versus surfactant concentration droplet size distributions and interfacial dilatational viscoelasticity.

The dynamic interfacial adsorption and demulsification behaviors of novel amphiphilic dendrimers

The dynamic surface tension and dilational viscoelasticity properties of amphiphilic polyamidoamine (PAMAM) dendrimers were investigated to probe the hydrophobic chain effect on the interfacial properties and the demulsification behaviors. The values of dynamic parameters n and t* representing diffusion speed of the molecules obtained according to the Rosen equation decreased with the increasing of bulk concentration. Taking the hydrophobic effect into consideration, the t* values decreased and n values increased with the increase of alkyl chain length, suggesting easier adsorption and faster diffusion for longer hydrophobic chain which was opposite to the tendency of traditional surfactants. Further dilational viscoelasticity studies demonstrated that the properties referring to adsorption and exchange-diffusion were probably affected by the aggregates conformation at the interface. Subsequently, from the demulsification experiments a conclusion can be drawn that the amphiphilic dendrimers with branched dendritic structure possesses superior properties of breaking W/O crude oil emulsions, showing a certain correlation to the dilational viscoelasticity properties.

Comparison between cucurbiturils and β-cyclodextrin interactions with cholesterol molecules present in Langmuir monolayers used as a biomembrane model

Specific surface techniques can probe the interaction of cholesterol (Chol) with substances that are able to host and/or sequester this biomolecule, provided that the additives are properly assembled at the interface. Reports on inclusion complexes of Chol with β-cyclodextrins exist in the literature. Here we compare the interaction of β-cyclodextrin and cucurbiturils with Chol present in Langmuir phospholipid (dipalmitoylphosphatidylcholine, DPPC) monolayers, used as a biomembrane model. Cucurbiturils, CB[n], comprise macrocyclic host molecules consisting of n glycoluril units. Classic surface pressure curves, dilatational surface viscoelasticity measurements, and fluorescence emission spectra and images obtained by time-resolved fluorescence of the corresponding Langmuir–Blodgett films have shown that homologues with 5 and 6 glycoluril units, CB[5] and CB[6], do not form inclusion complexes. Higher-order homologues, such as CB[7], are likely to complex with Chol with changes in the minimum molecular areas recorded for DPPC/Chol monolayers, the fluorescence decay lifetimes, and the dilatational surface viscosities of the monolayers generated in the presence of these molecules. Moreover, we proof the removal of cholesterol from the biomimetic interface in the presence of CB[7] by means of fluorescence spectra from the subphase support of monolayers containing fluorescent-labeled Chol.

Interfacial Dilatational Viscoelasticity of Human Meibomian Lipid Films

Purpose/Aim: The meibomian lipid layer is able to withstand the enormous stresses and deformations that occur during blinking due to the combination of its elastic and viscous properties. The purpose of this study was to measure the dilatational viscoelasticity of in vitro meibomian lipid films and compare how these properties differ between room temperature and physiological temperatures. Viscoelasticity was also compared with meibomian lipid films seeded with cholesterol or β-carotene (the levels of these lipid species change in disease states).Materials and methods: Dilatational viscoelasticity (E) was measured using an oscillating pendant drop method. Measurements were carried out on spread films at the air–water interface as a function of frequency (0.1256–12.56 rad/s) at various temperatures between 18–43 °C.Results: Generally, E gradually decreased as the overall temperature was increased. At both 37 and 20 °C, films demonstrated that the elastic modulus (E′) was more dominant than the viscous modulus (E″), indicating films were more solid-like than fluid-like, regardless of temperature. E′ and E″ were also dependant on frequency, indicating some molecular rearrangements of the lipid molecules as films were compressed and expanded. Films seeded with cholesterol or β-carotene showed a modest increase in the moduli.Conclusions: These results are consistent with previous findings which have predicted and indicated that the meibomian lipid layer is a viscoelastic film at the air–liquid interface. These properties are integral to how the tear film lipid layer is able to maintain its structure, and hence integrity of the ocular surface.

Langmuir and Langmuir–Blodgett films of capsules of haemoglobin at air/water and solid/air interfaces

Organized assemblies of capsules of haemoglobin (Hb), in the size range of 0.1 to 0.3 \(\upmu \) in Langmuir films have been studied at air/water interface below and above the isoelectric point. Spread films of these organizates suggest that there is no expulsion of individual particles or particle assemblies at the interface and the particles are stable. Dynamic surface tension and the associated dilational and shear visco-elasticity in these films suggest that the capsules are highly elastic. Multilayer films of the capsules using Langmuir–Blodgett technique have been fabricated by sequential deposition on solid surfaces. These films have been characterized by circular dichroism spectroscopy (CD), atomic force microscopy (AFM), quartz crystal microbalance (QCM) and Fourier transform infrared with reflection absorption spectroscopy (FTIR-RAS). No appreciable change in the secondary structural features of Hb is seen from CD studies indicating the stability of the protein in these organized assemblies. Sizes of these capsules change near the isoelectric point and large swollen multi-walled capsules are formed. The elastic films of capsules of Hb provide a useful post preparation approach for modification of the surface roughness, porosity, and permeability of pre-assembled polypeptide microcapsules. Organized capsules of haemoglobin in the size range 0.1 to 0.3 μ have been prepared using freeze-thaw technique. Large multiwalled capsules are formed near the isoelectric point of the protein. Langmuir films of the capsules show high elasticity and are stable at air/water interface.

Adsorption isotherm and equation of state for β-Lactoglobulin layers at the air/water surface

The adsorption behaviour of β-Lactoglobulin (BLG) at the air/water surface and the visco-elastic properties of the BLG adsorption layers are discussed in terms of quasi-equilibrium adsorption isotherms and equation of state gained by comparing a model with a set of experimental data obtained by bubble profile analysis tensiometry. The presented simultaneous characterization of the adsorption isotherm and the dilational visco-elasticity under dynamic and equilibrium conditions is based on measurements of the dynamic surface pressure and its response to sinusoidal bubble area variations. The thermodynamic model was applied to the set of experimental data under the assumptions of monolayer compressibility, surface dimerization and development of a secondary layer. The effect of the bubble surface age on the adsorption isotherm and equation of state, and also on the visco-elastic characteristics is discussed and it allows concluding that the existence of a bilayer structure, which is formed beyond a certain protein adsorption, is responsible for the observed relaxation processes.

Synergistic Interaction of Short-Chain Phospholipids in the Adsorbed Film and Micelles: Study by Surface Tension and Dilational Viscoelasticity Measurements

The aggregate formation and surface adsorption of aqueous binary mixture of short-chain phospholipids, dihexanoyl-phosphatidylcholine (DC6PC), and dioctanoyl-phosphatidylcholine (DC8PC), were examined by surface tension and dilational viscoelasticity measurements. The concentration versus composition diagram of aggregate formation was constructed by analyzing the surface tension data. The diagram demonstrated a synergetic effect that even when the mole fraction of DC8PC in the aqueous solution was 0.02, worm-like micelle was formed and furthermore the addition of DC6PC to DC8PC solution lowered the DC8PC concentration at which worm-like micelle formation starts, although DC6PC molecules do not form worm-like micelles solely. The phase diagram of adsorption was also constructed to elucidate the miscibility of two components in the adsorbed film. The calculated excess Gibbs energy of adsorption was negative, again suggesting a synergistic attractive intermolecular interaction between two species in the adsorbed film. A staggered arrangement was proposed as a favorable intermolecular arrangement. The dilational viscoelasticity was also measured by the electrocapillary wave method, and both storage and loss modulus showed a maximum at around the surface composition of the minimum of the excess Gibbs energy of adsorption.

Dilational surface viscoelasticity of protein solutions. Impact of urea

The dilational surface rheology is applied to solutions of globular proteins (bovine serum albumin and β-lactoglobulin) in presence of urea. The kinetic dependencies of the dynamic dilational surface elasticity become non-monotonic if the denaturant concentration exceeds a certain critical value indicating the adsorption of unfolded protein molecules. The unfolding in the surface layer occurs at lower urea concentrations than in the bulk phase similar to the case of mixed solutions of the proteins and guanidine hydrochloride. At the same time, the influence of urea on the dilational surface rheological properties of protein solutions has some peculiarities. In particular, the high values of the dynamic surface elasticity close to equilibrium indicate the limited flexibility of unfolded BLG molecules in the surface layer.

Dynamic surface properties of eco-friendly phenylalanine glycerol ether surfactants at the W/A interface

Dynamic surface tension and dilatational viscoelasticity data are presented for aqueous solutions of novel nonconventional eco-friendly phenylalanine glycerol ether surfactants, with 12 carbon atoms in the hydrophobic alkyl chain, PhGE12. Adsorption kinetics is studied in a broad range of concentrations and for time scales spanning from several milliseconds to several hours employing maximum bubble pressure tensiometry and drop profile tensiometry. Standard free energy of adsorption and diffusion coefficients for both short and long adsorption times are calculated and discussed. For short adsorption times diffusion coefficients lie in a physically reasonable range but for long adsorption times extremely low values are computed indicating the presence of an adsorption barrier. This barrier appears to mask any micellar kinetics effect for long adsorption times. Measurements of interfacial dilatational storage modulus and loss modulus indicate a visco-elastic character of the adsorption layer for all the examined concentrations and oscillation frequencies. Local peaks in the values of both moduli imply that structural changes occur with increasing concentration. However, these changes seem to be unrelated to the presence of micelles since they are observed at concentrations below the CMC.

Demulsification and Interfacial Properties of Crosslinking Phenol-Amine Resin Block Polyether Demulsifiers

Six novel crosslinking phenol-amine resin block polyether demulsifiers were synthesized for demulsification of surfactant-polymer flooding emulsion. The demulsification performances of these demulsifiers were investigated by conventional graduated bottle test. Their interfacial behaviors at water-oil interface were explored by dynamic interfacial tension and interfacial dilational viscoelasticity measurements. The results show that the demulsification efficiency is dependant on the hydrophilic-hydrophobic balance (HLB) value of these demulsifiers. It was also correlated to the interfacial activity and the dilational elasticity at the water-oil interface. The higher the HLB value of demulsifiers, the better the demulsification efficiency is.

Aggregation Behaviors of PEO-PPO-ph-PPO-PEO and PPO-PEO-ph-PEO-PPO at an Air/Water Interface: Experimental Study and Molecular Dynamics Simulation

The block polyethers PEO-PPO-ph-PPO-PEO (BPE) and PPO-PEO-ph-PEO-PPO (BEP) are synthesized by anionic polymerization using bisphenol A as initiator. Compared with Pluronic P123, the aggregation behaviors of BPE and BEP at an air/water interface are investigated by the surface tension and dilational viscoelasticity. The molecular construction can influence the efficiency and effectiveness of block polyethers in decreasing surface tension. BPE has the most efficient ability to decrease surface tension of water among the three block polyethers. The maximum surface excess concentration (Γ(max)) of BPE is larger than that of BEP or P123. Moreover, the dilational modulus of BPE is almost the same as that of P123, but much larger than that of BEP. The molecular dynamics simulation provides the conformational variations of block polyethers at the air/water interface.

Effects of Na–montmorillonite particles on the emulsification stability of polymer flooding produced water

Simulation experiments were conducted to investigate the effects of Na–montmorillonite (Na–Mt) on the emulsion stability of polymer flooding water. To study the stabilization mechanisms of Na–Mt particles in the emulsion system, the oil/water interfacial properties were investigated by measuring the zeta potential, interfacial tension and dilational viscoelasticity. The features of Na–Mt particles adsorbed on oil droplets were observed under optical microscopy. The results indicated that, with the increase of Na–Mt particles up to 200mg/L, the zeta potential became more negative, the interfacial tension decreased greatly, dilational viscoelasticity was enhanced and a stable oil–mineral aggregate (OMA) structure appeared, therefore, the polymer flooding produced water was stabilized. With further increases of Na–Mt particle concentrations, the zeta potential of oil droplets remained stable, the interfacial tension slightly increased, and the dilational viscoelasticity decreased. In this system, a larger OMA structure was apt to form, which could favor the treatment of polymer flooding produced water.

Fast dynamic interfacial tension measurements and dilational rheology of interfacial layers by using the capillary pressure technique

The oscillating drop and bubble analyzer (ODBA) is an experimental set-up based on the measurement of capillary pressure under static and dynamic conditions. It allows studies of slow and fast dynamic surface and interfacial tensions, following different growing and oscillating drop or bubble protocols, as well as determination of the dilational interfacial visco-elasticity of liquid interfacial layers. For the visco-elasticity studies, drops or bubbles are subjected to harmonic oscillations of area or volume in a broad frequency range, and the resulting harmonic capillary pressure response is analyzed by Fourier analysis. Also, transient relaxations can be easily performed, which are of particular importance for isodense systems. The limits of applicability for highly dynamic conditions are given by the hydrodynamics of the fluid flow inside the capillary tip and the pressure cell which depend on fluid properties, capillary tip size, and geometry. For the growing drop protocol, additional phenomena during drop formation and detachment play a significant role. For oscillating drops or bubbles, the highest accessible frequencies also depend on the absolute drop size and applied oscillation amplitude. In this work, the capability of the technique for measurements in the frequency range between 1 and 100Hz are discussed, and elasticity values at up to 80Hz were measured for the liquid–liquid interface.

Surface dilatational behavior of β-casein at the solution/air interface at different pH values

The surface tension and dilatational visco-elasticity isotherms for β-casein determined at pH 7 and 9 are essentially the same, but differ remarkably from those measured at the isoelectric point (i.e.p.) of the protein at pH 5. A recently developed thermodynamic model is applied to the experimental data, which were not only obtained at equilibrium, but also under quasi-equilibrium conditions. It turned out that such a model can be adequately applied to data obtained not too far from the equilibrium state of a protein adsorption layer. The change in the model parameters allows to understand slow changes in the structure of the adsorption layer. Even at pH 5, where β-casein is most hydrophobic and in its most compact conformation, the data point to the fact that conformational changes may happen at the interface upon adsorption.