Interfacial Dilation Research Articles

Effect of particle size of sand and surface asperities of reinforcement on their interface shear behaviour

This paper investigates the effect of particle size of sand and the surface asperities of reinforcing material on their interlocking mechanism and its influence on the interfacial shear strength under direct sliding condition. Three sands of different sizes with similar morphological characteristics and four different types of reinforcing materials with different surface features were used in this study. Interface direct shear tests on these materials were performed in a specially developed symmetric loading interface direct shear test setup. Morphological characteristics of sand particles were determined from digital image analysis and the surface roughness of the reinforcing materials was measured using an analytical expression developed for this purpose. Interface direct shear tests at three different normal stresses were carried out by shearing the sand on the reinforcing material fixed to a smooth surface. Test results revealed that the peak interfacial friction and dilation angles are hugely dependent upon the interlocking between the sand particles and the asperities of reinforcing material, which in turn depends on the relative size of sand particles and asperities. Asperity ratio (AS/D50) of interlocking materials, which is defined as the ratio of asperity spacing of the reinforcing material and the mean particle size of sand was found to govern the interfacial shear strength with highest interfacial strength measured when the asperity ratio was equal to one, which represents the closest fitting of sand particles into the asperities. It was also understood that the surface roughness of the reinforcing material influences the shear strength to an extent, the influence being more pronounced in coarser particles. Shear bands in the interface shear tests were analysed through image segmentation technique and it was observed that the ratio of shear band thickness (t) to the median particle size (D50) was maximum when the AS/D50 was equal to one.

Interfacial and foaming characterisation of mixed protein-starch particle systems for food-foam applications

This work presents mixed protein-starch systems as effective foaming agents and stabilisers. The starch size and hydrophobicity play a dominant role in determining the levels of synergy observed. Egg White Protein (EWP) and Pea Protein Isolate (PPI) were selected at two concentrations (0.5, 1 wt. %) along with three starch species of concentrations between 0.5, 1, 3 & 5wt. %. Two commercial OSA-modified starches are compared to a native granule and its heat-treated counter part. The system's effectiveness to incorporate air (overrun) as well as its capacity to hold structure (half life) is evaluated. starch's physical properties (contact angle and size) and their effect on the nature of the Air/Water (A/W) interface (interfacial dilatation rheology, surface tension) are also explored. The effect of protein species as well as starch size and hydrophobicity on foam stability is determined and discussed. The study demonstrates that addition of OSA modified starch (0–5wt%) to (EWP) foams can enhance foam stability by up to 1200% without compromising the foaming capacity, mainly due to a hypothesised exclusion volume effect. Where as the larger heat-treated starch granule is found to increase stability of wet foams by 800%, through a combination of mechanisms.

Effect of Demulsifier Structures on the Interfacial Dilational Properties of Oil–Water Films

The dilational properties of a branch-shaped polyether-type nonionic demulsifier (PEB), a comb-shaped polyether-type nonionic demulsifier (PEC), and a star-shaped polyether-type nonionic demulsifier (PES) at the decane–water interfaces were investigated by Langmuir trough method through oscillating barrier and interfacial tension relaxation methods, which are mainly in the influences of oscillating frequency and bulk concentration on dilational properties. Meanwhile, the effect of demulsifiers on interfacial dilational modulus of diluted crude oil was also explored. The experimental results indicate that all demulsifiers can decrease the dilational modulus of diluted crude oil at the experimental concentration. The addition of PEB causes the dilational modulus of crude oil to be lower than that at the water–decane interface. The demulsifier PEC has a similar effect with PES to influence the interfacial film of crude oil: at low concentration, the dilational modulus of mixed interfacial film is lower than that of demulsifier alone, while at high concentration, the dilational modulus of mixed interfacial film is slightly higher than that of demulsifier alone. The dependence of static modulus on the bulk concentration is consistent with the trend of interfacial dilational modulus with concentration for demulsifiers PEB, PEC, and PES. The studies about the structure modulus show that the new demulsifiers PEC and PES have a stronger ability than branch-shaped demulsifier PEB to destroy the interfacial film.

Effect of Hydrophobic Chain Length on the Interfacial Dilational Rheological Properties of Polyoxyethylene Sorbitan Fatty Acid Ester

Effect of Hydrophobic Chain Length on the Interfacial Dilational Rheological Properties of Polyoxyethylene Sorbitan Fatty Acid Ester

Structural and mechanical properties of Ni60Nb40 amorphous alloy particle reinforced Al-based composites produced by microwave-assisted rapid sintering

Novel Al-composites were produced by reinforcing pure Al with varying volume fractions of Ni60Nb40 amorphous alloy powders (Vp) using microwave-assisted two-directional rapid sintering, and subsequent hot extrusion. The composites were investigated for their structural and mechanical properties. Structural analyses reveal: (a) uniform distribution of reinforcement, (b) absence of interfacial products, (c) structural dilatation and change in aspect ratio of reinforcement at 25% Vp and (d) retention of amorphous structure of reinforcement at all Vp.Electrical resistivity of composites increases with increase in Vp. Microhardness and compressive strength properties increase remarkably with Vp (∼130% and ∼100% respectively, at 25% Vp). The composites do not fracture under compressive loading even at ∼50% strain. Tensile tests show a significant enhancement in strength of ∼60% at 25% Vp. The report on the tensile behavior of amorphous alloy/glass-reinforced composites is the first of its kind. The mechanical properties of the developed composites have been compared with those of the existing composites and with the theoretical estimates. The mechanical behavior is discussed based on processing–structure–property correlation. The results highlight the potential of amorphous/glassy alloys as better alternative reinforcements to produce high performance composites. They also show microwave sintering as an effective processing method to produce such composites.

Surface rheological properties of liquid–liquid interfaces stabilized by protein fibrillar aggregates and protein–polysaccharide complexes

In this study we have investigated the surface rheological properties of oil–water interfaces stabilized by fibrils from lysozyme (long and semi-flexible and short and rigid ones), fibrils from ovalbumin (short and semi-flexible), lysozyme–pectin complexes, or ovalbumin–pectin complexes. We have compared these properties with those of interfaces stabilized by the native proteins. The surface dilatational and surface shear moduli were determined using an automated drop tensiometer and a stress controlled rheometer with biconical disk geometry. Results show that interfaces stabilized by complexes of these proteins with high-methoxyl pectin have higher surface shear and dilatational moduli than interfaces stabilized by the native proteins only. The interfaces stabilized by ovalbumin and lysozyme complexes have comparable shear and dilatational moduli though ovalbumin–pectin complexes are twice as large in radius as lysozyme–pectin complexes. Under most of the experimental conditions, interfaces stabilized by fibrils have the highest surface rheological moduli. The difference between long semi-flexible lysozyme fibrils or short rigid lysozyme fibrils is not pronounced in interfacial dilation rheology but significant in interfacial shear rheology. The complex surface shear moduli of interfaces stabilized by long semi-flexible fibrils are about 10 times higher than those of interfaces stabilized by short rigid fibrils, over a range of bulk concentrations. Interfaces stabilized by short and more flexible ovalbumin fibrils have a significantly higher surface shear modulus than those stabilized by longer and more rigid lysozyme fibrils. This study has shown that the use of such supra-molecular structural building blocks creates a wider range of microstructural features of the interface, with higher surface shear and dilatational moduli and a more complex dependence on strain.

Influence of Oleic Acid and Electrolyte on the Interfacial Dilational Properties of Surfactant/Polymer Systems at the Decane-Water Interface

The dilational properties of partly hydrolyzed polyacrylamide (HPAM) and 4,5-diheptyl-2-propylbenzene sulfonate (377) mixed systems in the absence or presence of electrolyte or oleic acid at the oil-water interface have been described by means of the oscillating barriers method and the interfacial tension relaxation method. The polymer plays different roles in influencing the nature of polymer-surfactant adsorbed layers at different surfactant concentrations. At low surfactant concentration, the addition of polymer perhaps weakens the “entanglement” of long alkyl chains, which decreases strikingly the dilational modulus of the adsorbed layer. At high surfactant concentration, the addition of the polymer increases the dilational modulus due to the hydrophobic interactions between polymer and surfactant molecules. On the case of adding electrolyte, the frequency dependence of dilational modulus increases due to the enhancement of exchange process of surfactant molecules and bivalent cation has more obvious effect than Na ion. Oleic acid plays dual roles in controlling interfacial dilational properties of mixed adsorption films: a small quantity of oleic acid increases the dilational modulus by forming densely packed mixed adsorption layer with surfactant molecules, while the superfluous addition of oleic acid could decrease the dilational modulus mainly due to the weakening of the “entanglement” among long alkyl chains in surfactant molecules.

Effect of Molecular Weight on the Interfacial Dilational Viscoelasticity of Anionic Polyelectrolyte/Surfactant Systems

In this article, the effect of molecular weight on the interfacial tension and interfacial dilational viscoelasticity of polystyrene sulfonate/surfactant adsorption films at the water-octane interface have been studied by spinning drop method and oscillating barriers method respectively. The experimental results show that different interfacial behaviors can be observed in different type of polyelectrolyte/surfactant systems. PSS/cationic surfactant CTAB systems show the classical behavior of oppositely charged polyelectrolyte/surfactant systems and can be well explained by electrostatic interaction. Molecular weight of PSS plays a crucial role in the nature of adsorption film. The complex formed by CTAB and higher molecular weight PSS, which has larger dimension and stronger interaction, results in higher dilational modulus at lower surfactant bulk concentration. In the case of PSS/anionic surfactant SDS systems, the co-adsorption of PSS at interface through hydrophobic interaction with alkyl chain of SDS leads to the increase of interfacial tension and the decrease of dilational modulus at lower surfactant bulk concentration. For PSS/nonionic surfactant T × 100 systems, PSS may form a sublayer contiguous to the aqueous phase, which has little effect on interfacial tension but slightly decreases dilational modulus.

Effect of Hydrophobically Modified Polyacrylamide on Interfacial Dilational Rheological Properties of Crude Oil Components

The effect of hydrophobically modified polyacrylamide (HMPAM) on the dilational rheological properties of interfacial films containing acidic components or asphaltenes in petroleum crude oil was investigated by drop shape analysis method. The influence of surface-active component concentration on the dilational rheological behavior was investigated. Experimental results show that the dilational modulus is approximately 100 mN·m-1 for a 1750 mg·L-1 HMPAM solution. This is due to the formation of an interfacial structure by a hydrophobic interaction among HMPAM molecules. As the interfacial film ages, the acidic component molecules adsorb onto the interface and form mixed complexes with the hydrophobic parts of the HMPAM molecules. These interactions reduce the dilational modulus by a fast exchange process and the elasticity of the structure improves because of an enhanced hydrophobic interaction among the HMPAM molecules. For asphaltenes, the nature of the interfacial film is controlled by both the structure of HMPAM and the interfacial complex formed by pure asphaltene molecules because of their relatively larger molecular sizes as well as their strong intermolecular interactions, which leads to a slight decrease in the dilational modulus compared with the pure HMPAM system.

Effect of Electrolyte on the Interfacial Dilational Properties of Sodium 4,5-Diheptyl-2-propylbenzene Sulfonate at the Oil–Water Interface

The dilational viscoelastic properties of 4,5-diheptyl-2-propylbenzene sulfonate (377) in the presence or absence of electrolyte were investigated by means of two methods: the interfacial tension response to sinusoidal area variations and the relaxation of an applied stress. The higher dilational modulus of 377 than ordinary surfactant indicates that the strength against perturbation of interfacial layer of the former is greater. This may due to the two long and flexible branched alkyl chains, which are easily cross-linked and entangled. Moreover, the results reveal that the added electrolyte results in screening of electrostatic interactions between the ionized groups, which decreased the interfacial dilational modulus.

Investigation of Macromolecule/Surfactant Interaction by Interfacial Dilational Rheology Method

The applications of interfacial dilational rheology method in studying macromolecule/surfactant system were systematically summarized combing with our work. Many previous studies have indicated that this method can be used to probe the microcosmic property of interfacial layer. This is done by analyzing the interfacial dilational viscoelasticity and characteristic parameters of the interfacial relaxation process. The interaction mechanism between macromolecule and surfactant could thus be investigated. The method can be applied in practice.

Exploring lattice effects on transport properties in La0.7Sr0.3MnO3/Al2O3 superlattices

Superlattice modulation and interfacial dilatation in manganite/alumina multilayers were used to explore lattice effects on transport behaviour. Epitaxial growth and high quality of stacking as well as structural coherency were confirmed by x-ray measurements. As the measure of lattice distortion, the average lattice spacing, structural coherency length, Curie temperature, magnetization, coercive field Hc as well as resistance are found to be functions of the interface fraction. Accordingly, we divided each manganite layer into two parts, i.e., weakly distorted ‘innermost’ atomic layers and strongly dilated interfacial atomic layers, as is well clarified by observation of two component magnetization loops and huge variation in resistance measured with current in and perpendicular to plane (i.e. CIP and CPP). The low-resistive innermost part with a ‘bulk’-like soft magnetic behaviour functions as a conductance channel for the CIP case, whereas the high-resistive interfacial part rules the CPP data, leading to a low-magnetotunnelling effect at 4.2 K and an enhanced colossal magnetoresistance at the relevant transition temperature.

RELAXATION OF ASPHALTENES AT THE TOLUENE/WATER INTERFACE: DIFFUSION EXCHANGE AND SURFACE REARRANGEMENT

Upon adsorption at the oil/water interface, asphaltenes slowly form a glassy interphase. This robust, asphaltene-rich interphase is likely the reason for prolonged stability of crude oil/water emulsions and for the propensity of asphaltenic crude oils to alter the wettability of reservoirs. Here we adopt interfacial dilatation rheology using the oscillating pendant drop with axisymmetric drop shape analysis (ADSA) to investigate the relaxation mechanisms of asphaltenes adsorbed at the toluene/water interface. We compare classical viscoelastic models with the measured rheologic data and find that the frequency response of the dilatational moduli fits a combination of diffusion-exchange and surface-rearrangement mechanisms. The combined relaxation model is verified by solvent washing the asphaltenes from the interface and measuring the dilatational response of the resulting irreversibly adsorbed species. After washout, the oil-phase diffusion component of the frequency response disappears, and the relaxation time of the adsorbed film increases by an order of magnitude. Since the studied asphaltenes prove insoluble in the synthetic aqueous brine (pH = 8.0), this result suggests that reversibly exchanging species in the oil phase weakens an interconnected asphaltene-gel/glass phase at the interface. Our experiments show, for the first time, that most of the surface-active asphaltenic molecules are irreversibly adsorbed from the oil phase.

Measurement of the kinetic rate constants for the adsorption of superspreading trisiloxanes to an air/aqueous interface and the relevance of these measurements to the mechanism of superspreading

Super-spreading trisiloxane surfactants are a class of amphiphiles which consist of nonpolar trisiloxane headgroups (((CH 3) 3SiO) 2Si(CH 3)(CH 2) 3) and polar parts composed of between four and eight ethylene oxides (ethoxylates, OCH 2CH 2). Millimeter-sized aqueous drops of trisiloxane solutions at concentrations well above the critical aggregate concentration spread rapidly on very hydrophobic surfaces, completely wetting out at equilibrium. The wetting out can be understood as a consequence of the ability of the trisiloxanes at the advancing perimeter of the drop to adsorb at the air/aqueous and aqueous/hydrophobic solid interfaces and to reduce considerably the tensions of these interfaces, creating a positive spreading coefficient. The rapid spreading can be due to maintaining a positive spreading coefficient at the perimeter as the drop spreads. However, the air/aqueous and solid/aqueous interfaces at the perimeter are depleted of surfactant by interfacial expansion as the drop spreads. The spreading coefficient can remain positive if the rate of surfactant adsorption onto the solid and fluid surfaces from the spreading aqueous film at the perimeter exceeds the diluting effect due to the area expansion. This task is made more difficult by the fact that the reservoir of surfactant in the film is continually depleted by adsorption to the expanding interfaces. If the adsorption cannot keep pace with the area expansion at the perimeter, and the surface concentrations become reduced at the contact line, a negative spreading coefficient which retards the drop movement can develop. In this case, however, a Marangoni mechanism can account for the rapid spreading if the surface concentrations at the drop apex are assumed to remain high compared to the perimeter so that the drop is pulled out by the higher tension at the perimeter than at the apex. To maintain a high apex concentration, surfactant adsorption must exceed the rate of interfacial dilation at the apex due to the outward flow. This is conceivable because, unlike that at the contact line, the surfactant reservoir in the liquid at the drop center is not continually depleted by adsorption onto an expanding solid surface. In an effort to understand the rapid spreading, we measure the kinetic rate constants for adsorption of unaggregated trisiloxane surfactant from the sublayer to the air/aqueous surface. The kinetic rate of adsorption, computed assuming the bulk concentration of monomer to be uniform and undepleted, represents the fastest that surfactant monomer can adsorb onto the air/aqueous surface in the absence of direct adsorption of aggregates. The kinetic constants are obtained by measuring the dynamic tension relaxation as trisiloxanes adsorb onto a clean pendant bubble interface. We find that the rate of kinetic adsorption is only of the same order as the area expansion rates observed in superspreading, and therefore the unaggregated flux cannot maintain very high surface concentrations at the air/aqueous interface, either at the apex or at the perimeter. Hence in order to maintain either a positive spreading coefficient or a Marangoni gradient, the surfactant adsorptive flux needs to be augmented, and the direct adsorption of aggregates (which in the case of the trisiloxanes are bilayers and vesicles) is suggested as one possibility.

Bubble detachment by diffusion-controlled surfactant adsorption

The effect of the diffusion-controlled adsorption of the surfactant Triton X-100 on detachment of gas bubbles adherent to the wall in pipe flow is studied. Air bubbles of known volume (scaled bubble dimension λ=0.8, 1.0, 1.5) are maintained in tubes inclined at 25°, 45°, 65°, or 90°. Triton X-100 is infused into the bulk flow to achieve a final mixed bulk concentration of either 10% or 100% of the critical micelle concentration. Pressure and flow waveforms are recorded, and video images of bubbles before and during exposure to the surfactant are captured. Surfactant-induced reductions of the surface tension and contact angle lead to distinct regimes of dynamic bubble behavior including static and oscillatory interfacial deformation, deformation with axial displacement, and complete bubble detachment from the wall. The surfactant-mediated responses depend on the interrelated effects of Triton X-100 concentration, bubble size, and tube angle. A high bulk concentration of Triton X-100 produces rapid changes in bubble shape and promotes wetting, increasing the potential for bubble detachment. Bubble detachment occurs more readily with larger bubble volume. For vertical tubes (i.e. no contact forces present) and non-vertical tubes (i.e. contact forces present), the bubble may be displaced axially in either the direction of or opposite to the bulk flow direction following introduction of Triton X-100. Bubble axial motion and detachment result from the surfactant effects on contact line mechanics. For moving contact lines, the contact line velocities corresponding to rates of shrinkage of de-wetted surface area (or, alternatively, rates of gas–liquid interfacial dilation) along with time-dependent contact front length are determined from the experimental data. Potential effects of Triton X-100 on interfacial remobilization are described. Soluble surfactants have the potential to be used for dislodging gas bubbles adherent to a pipe wall by intentional manipulation of interfacial shape and wetting properties.

Interfacial dilational behaviour of adsorbed β-lactoglobulin layers at the different fluid interfaces

β-Lactoglobulin adsorption layers at the interfaces solution/air, /tetradecan and /sunflower oil were characterised by dynamic interfacial tension measurements and harmonic drop oscillation experiments in a time scale of some seconds. Axialsymmetric drop shape analysis (ADSA) was used to calculate drop volume, area and interfacial tension. Within a definite range of drop volume amplitude, the oscillation of the surface tension is harmonic and interfacial dilation parameters can be determined. Dependence of the dilational parameters on the amplitude and frequency of drop volume oscillation were determined and methodical demands are given for this special kind of ADSA application. The concentration of interfacial saturation is minimal at the interface with sunflower oil. Interfacial dilational elasticities, and viscosities are maximal at the saturation concentration of all systems investigated. The dilational viscosities are maximal in the frequency range 0.007–0.011 Hz and characterise molecular rearrangement processes in the adsorption layer. Interfacial dilational elasticity and viscosity are the largest at the interface with air. They are the smallest at the interface with sunflower oil. Similarities and differences of the systems investigated are discussed by taking into account the adsorption behaviour and the solvatation of different apolar and polar parts of the protein molecules in the neighbouring phase.

Flocculation and coalescence of micron-size emulsion droplets

We analyze the relative importance of droplet deformation, surfactant transfer and interfacial rheology for the properties and stability of emulsions. The appearance of deformation (flattening or film) in the zone of contact of two interacting droplets has the following consequences. It enhances the importance of the surface forces of intermolecular origin and gives rise to contributions from the interfacial dilatation and the bending energy. The flattening increases the viscous dissipation in the gap between two colliding drops and thus prolongs the lifetime of the doublet of two such drops. The critical thickness of the gap also depends on whether the drops are deformed or non-deformed. The factors which facilitate the flattening in the zone of contact between two emulsion drops are the increase in droplet size, the decrease in interfacial tension, the bending energy for water-in-oil emulsions, the increase in droplet–droplet attraction and the suppression of droplet–droplet repulsion. The presence of surfactant strongly affects the interfacial tension, the bending moment, and influences all kinds of DLVO and non-DLVO surface forces operative in the gap between two droplets. The rheological and dynamic properties of the surfactant adsorption monolayers (Gibbs elasticity, surface diffusivity, surface viscosity, and adsorption relaxation time) are major factors for the stability of emulsions under dynamic conditions. The solubility of the surfactant in one of the two phases can determine whether oil-in-water or water-in-oil emulsion will be formed. A criterion for emulsion stability accounting for the interplay of all thermodynamic and hydrodynamic factors mentioned above is obtained. It provides an interpretation and generalization of the Bancroft rule.

A Growing Drop Technique for Measuring Dynamic Interfacial Tension

A novel, growing drop technique is described for measuring dynamic interfacial tension due to sorption of surface-active solutes. The proposed method relates the instantaneous pressure and size of expanding liquid drops to the interfacial tension and is useful for measuring both liquid/gas and liquid/liquid tensions over a wide range of time scales, currently from 10 ms to several hours. Growing drop measurements on surfactant-free water/ air and water/octanol interfaces yield constant tensions equal to their known literature values. For surfactant-laden, liquid drops, the growing drop technique captures the actual transient tension evolution of a single interface, rather than interval times as with the classic maximum-drop-pressure and drop-volume tension measurements. Dynamic tensions measured for 0.25 m M aqueous 1-decanol solution/air and 0.02 kg/m 3 aqueous Triton X-100 solution/dodecane interfaces show nonmonotonic behavior, indicating slow surfactant transport relative to the imposed rates of interfacial dilatation. The dynamic tension of a purified and fresh 6 m M aqueous sodium dodecyl sulfate (SDS) solution/air interface shows only a monotonic decrease, indicating rapid surfactant transport relative to the imposed rates of dilatation. Conversely, an aged SDS solution, naturally containing trace dodecanol impurities, exhibits dynamic tensions which reflect a superposition of the rapidly equilibrating SDS and the slowly adsorbing dodecanol.

Micromechanical description of curved interfaces, thin films, and membranes: I. Quasistatics

Slow quasistatic deformations of a fluid interface or membrane are investigated theoretically from a micromechanical viewpoint. The surface rate-of-strain tensor is characterized by its invariants, α and β, which account for the interfacial dilation and shear, respectively. The macroscopic interfacial stretching and shearing tensions and the bending and torsion moments are expressed through integrals over the components of the pressure tensor. The results are applied to derive the Gibbsian fundamental thermodynamic equations of an arbitrarily curved interface from the fundamental equations of the adjacent bulk phases. Then, by means of a variational principle, the conditions for interfacial mechanical equilibrium are derived.

Observation and interpretation of the atomic structure of a [Sgrave] = 19/[110] (331) tilt boundary in Au thin films

Abstract The atomic structure of a (331) [Sgrave] = 19/[110] tilt boundary prepared from an Au bicrystal has been investigated by very high resolution transmission electron microscopy. It has also been possible to confirm independently the type of contrast obtained in such a micrograph by dynamical diffraction and computer image simulations and correlate the image features to the atomic position data. Close agreement has been achieved between two relaxed boundary structure models and the computer-enhanced [Sgrave]=19 micrograph viewed along the tilt axis direction. Direct measurements of the interfacial dilatation of the (331) planes parallel to the interface and the relative translations of the two crystals on either side of the interface have also been made.