Interfacial Shear Rheology Research Articles

Interfacial rheology, emulsifying property and emulsion stability of glyceryl monooleate-modified corn fiber gum

The present work aims to develop novel glyceryl monooleate (GMO)–modified corn fiber gum (CFG) emulsifiers (GMO–CFG) and investigate the role of the interfacial properties on emulsion stability. GMO–CFG with different degrees of substitution (DS) were prepared, and their interfacial rheology and emulsification were appraised for potential applications in stabilizing oil/water emulsions. Various oil/water interfacial properties (i.e., adsorption kinetics, viscoelasticity, and adsorbed amount) were determined as a function of DS by using interfacial shear rheology and quartz crystal microbalance with dissipation monitoring techniques. Hydrophobically modified CFG provides an increased capacity to produce fine droplets and stable emulsions. Esterification and its degree exert non-negligible effects on the critical micelle concentration, interfacial tension, interfacial adsorbed amount, and viscoelasticity of the interfacial layer. The rheological properties of the interfacial layers play an important role in macroscopic emulsion stability.

Effect of Arthrospira platensis microalgae protein purification on emulsification mechanism and efficiency

In light of environmental concerns and changing consumer demands, efforts are increasing to replace frequently used animal-based emulsifiers. We demonstrate the interfacial network formation and emulsifying potential of Arthrospira platensis protein extracts and hypothesize a mechanistic change upon progressing purification. A microalgae suspension of A. platensis powder in phosphate buffer solution (pH 7, 0.1 M) was homogenized and insoluble components separated by centrifugation. Proteins were precipitated at the identified isoelectric point at pH 3.5 and diafiltrated. In interfacial shear rheology measurements, the build-up of an interfacial viscoelastic network was faster and final network strength increased with the degree of purification. It is suggested that isolated A. platensis proteins rapidly form an interconnected protein layer while coextracted surfactants impede protein adsorption for crude and soluble extracts. Emulsions with 20 vol % medium chain triglycerides (MCT) oil could be formed with all extracts of different degrees of purification. Normalized by protein concentration, smaller droplets could be stabilized with the isolated fractions. For potential applications in food, pharma and cosmetic product categories, the enhanced functionality has to be balanced against the loss in biomass while purifying microalgae proteins or other alternative single cell proteins.

Viscoelastic characterization of the crosslinking of β-lactoglobulin on emulsion drops via microcapsule compression and interfacial dilational and shear rheology

HypothesisInterfacial rheology provides insight into the mechanical properties of adsorption layers on liquid–liquid interfaces, which mediates the stability of emulsion droplets. The use of capsule compression at the scale of an emulsion droplet to probe the interfacial rheology may open up the possibility of testing the interfacial rheological properties of droplets with complex histories and extremely small volumes found in many applications. ExperimentsThe time dependent interfacial rheological behavior of β-lactoglobulin adsorption layers on an oil/water interface in the native and crosslinked state was extracted using small oscillatory indentation with atomic force microscopy (AFM). The results of this novel model and experimental approach were compared to the well-established techniques of interfacial shear rheology (ISR) and dilational pendant drop tensiometry that were performed on analogous interfaces. FindingsThe tan δ measured between the ISR and AFM measurements provide similar results in an overlapping frequency range, but the viscoelastic moduli G’ and G’’ differ by several orders of magnitude. This is most likely the result of the different flow fields and the low deformation of the AFM measurements compared to dilational and shear flow fields.

Viscoelastic properties of interfacial lignosulfonate films and the effect of added electrolytes

New evidence is presented, which confirmed interfacial gelling of lignosulfonates in presence of di- and trivalent cations. In this article, the viscoelastic properties of lignosulfonate films at the water-xylene interface were studied by dilatational interfacial rheology and interfacial shear rheology. Both techniques showed that increasing lignosulfonate concentration would first increase and then decrease the interfacial modulus. The same trend was observed for increasing salinity. The maximum interfacial modulus corresponded with lignosulfonate aggregation or precipitation and accounted for the best emulsion stability. The film strength increased progressively with the cation charge number. It was argued that multivalent cations provided intermolecular bridging between lignosulfonate molecules, which increased film strength and led to gelling. The decrease of interfacial film strength at high salinity was explained by two mechanisms: (1) For sodium cations, the polyelectrolyte contraction at high ionic strength yielded screening of the functional groups, which are deemed responsible for attractive interactions between lignosulfonate molecules or aggregates. (2) For calcium and aluminum cations, precipitation would reduce the effective bulk concentration, yielding a lower surface coverage. Modelling of the interfacial properties was conducted in addition, which showed that lignosulfonate adsorption was not diffusion-controlled and that lignosulfonate aggregation was affecting the adsorption process. In conclusion, our results revealed a more detailed picture of the mechanisms, which govern the interfacial behavior and properties of lignosulfonates.

Effects of ultrasonic conditions on the interfacial property and emulsifying property of cellulose nanoparticles from ginkgo seed shells

Cellulose microparticles from ginkgo seed shells were treated by ultrasonic treatments within the selected output powders (150–600 W) and durations (10–60 min) to produce cellulose nanoparticles. The main aim of this study was to investigate effects of ultrasonic conditions on the interfacial property and emulsifying property of those cellulose nanoparticles. Compared to ultrasonic output powers, ultrasonic durations showed the greater influence on morphology and physical properties of cellulose nanoparticles. Atomic force microscopy revealed that noodle-like cellulose particles with 1100 nm in length gradually became the short rod-like nanoparticles with 300 nm in length with increasing of ultrasonic duration from 10 min to 60 min. Moreover, results of contact angles indicated that ultrasound could significantly improve hydrophobicity of cellulose nanoparticles. The interfacial shear rheology showed that although all cellulose nanoparticles exhibited the similar interface adsorption behavior which showed the initial lag-phase of adsorption, followed by the interface saturation, the time of this initial lag-phase was affected by ultrasonic conditions. The increase of ultrasonic duration and ultrasonic power could shorten the time of this initial lag-phase, suggesting the resulting cellulose nanoparticles easier adsorption at the O/W interface. It was probably attributed to its small size and high hydrophobicity induced by intense ultrasonic treatments. Meanwhile, the cellulose nanoparticles with small size and higher hydrophobicity exhibited the better emulsifying ability to stabilize oil-in-water emulsions due to the formation of the viscoelastic interfacial film. This study improved understanding about changes in interfacial and emulsifying properties of cellulose nanoparticles caused by ultrasonic treatments.

Ion-Mediated Cross-linking of Biopolymers Confined at Liquid/Liquid Interfaces Probed by In Situ High-Energy Grazing Incidence X-ray Photon Correlation Spectroscopy.

As manifested in biological cell membranes, the confinement of chemical reactions at the 2D interfaces significantly improves the reaction efficacy. The interface between two liquid phases is used in various key processes in industries, such as in food emulsification and floatation. However, monitoring the changes in the mechanics and dynamics of molecules confined at the liquid/liquid interfaces still remains a scientific challenge because it is nontrivial to access the interface buried under a liquid phase. Herein, we report the in situ monitoring of the cross-linking of polyalginate mediated by Ca2+ ions at the oil/water interface by grazing incidence X-ray photon correlation spectroscopy (GIXPCS). We first optimized the reaction conditions with the aid of interfacial shear rheology and then performed GIXPCS using a high-energy synchrotron X-ray beam (22 keV) that guarantees sufficiently high transmittance through the oil phase. The intensity autocorrelation functions implied that the formation of a percolated network of polyalginate is accompanied by increasing relaxation time. Moreover, the relaxation rate scales linearly with the momentum transfer parallel to the interface, suggesting that the process is driven by hyperdiffusive propagation but not by Brownian diffusion. Our data indicated that high-energy GIXPCS has potential for in situ monitoring of changes in the dynamics of polymers confined between two liquid phases.

Interfacial and emulsion characterisation of chemically modified polysaccharides through a multiscale approach

HypothesisThe structural modification of natural emulsifiers may greatly impact their interfacial behaviours and bulk properties. The relationship between the microscopic interfacial viscoelasticity and the macroscopic emulsion stability in emulsifiers with different degrees of modification can be clarified using a multiscale approach. ExperimentsA polysaccharide emulsifier of corn fibre gum (CFG) with different octenyl succinate anhydride (OSA) contents was used to obtain a broad variety of interfacial properties. Interfacial adsorption kinetics and viscoelastic responses were measured by combining interfacial shear rheology and quartz crystal microbalance with dissipation monitoring, and the emulsion properties (droplet size and physical stability) at other scales were evaluated. FindingsCompared with native CFG, esterified CFG formed thick interfacial films with higher elasticity and viscosity, and their corresponding emulsions showed greater stability. There exists a satisfactory correlation between interfacial rheological properties and emulsion stability. However, such a satisfactory correlation can not be established among the degree of esterification of CFG, interfacial viscoelasticity and stability since depletion flocculation might occur in the emulsion stabilized by the OSA-CFG with the highest OSA content, which induced inferior bulk stability but exerted no impact on the measured interfacial properties. We propose that the depletion flocculation is responsible for this imperfection and provide detailed explanations.

Relationship between interfacial and foaming properties of a Porphyra dioica seaweed protein concentrate

Porphyra dioica macroalgae can be regarded as a food-grade protein source that can be used for the stability of dispersed food systems. This work is focused on the foaming properties of a seaweed protein concentrate (SWE) from Porphyra dioica . The characterisation of air-water (A/W) interfacial layers formed after the SWE adsorption was carried out by means of interfacial tension, interfacial viscoelastic measurements and step deformation tests. These results were related to those obtained for SWE stabilized foams. Interfacial shear measurements indicate that not extensive protein-protein interactions at the A/W interface were developed (G' s = 1.0 ± 0.1·10 −2 mPa m), whereas the dilatational response (E' s = 23.5 ± 0.5 mN/m) match with the formation of a rigid interface as a result of a densely packed structure. Even if the foaming properties obtained for SWE (overall foam capacity, OFC, = 0.74 ± 0.01 mL/s) are similar to those reported for other commercial protein systems, its lower stability (t 1/2 = 204 ± 4 s) would indicate the need of adding stabilizers for an adequate shelf life of the final food product. The suitability of combining dilatational and interfacial shear rheology to predict the dynamics of dispersed systems was proven to be relevant to acquire insights of complex interfaces. • Porphyra dioica algae could be a food-grade protein source for dispersed systems. • Dilatational response indicated the formation of a rigid interface. • The weak interfacial shear response suggested the formation of a densely packed structure. • Dilatational and interfacial shear rheology was combined to predict the dynamics of foams. • Foaming properties were similar to those reported for commercial protein systems.

Interfacial properties of cellulose nanoparticles with different lengths from ginkgo seed shells

Cellulose microparticles from ginkgo seed shells were treated by high-pressure homogenization (HPH) processing ranging from 10 to 70 MPa to produce cellulose nanoparticles with different lengths. The aim of this study was to evaluate the interfacial behavior of those resulting nanoparticles using the interfacial tension and interfacial shear rheology. The results showed that although all cellulose nanoparticles lowered the interfacial tension, the interfacial behavior of nanoparticles with different lengths are different. The cellulose particles obtained from 10 MPa treatment (H-10) showed limited adsorption due to their long size and electrostatic repulsion. The strong entangled network structure was observed from cellulose nanoparticles obtained from 30 to 50 MPa treatment (H-30 and H-50). This entangled network structure probably caused faster interfacial saturation and contributed to the formation of the interfacial film with fibril entanglements. The cellulose nanoparticles obtained from 70 MPa treatment (H-70) were relatively easier to adsorb at the oil/water interface to reduce the interfacial tension and form a discontinuous monolayer due to their short size and higher hydrophobicity. Adsorbed nanoparticles layers were visualized by atomic force microscopy at planar Langmuir films, revealing the structure of formed interfacial layers is related to particle length. Emulsions stabilized by H-10 exhibited the bad storage stability because H-10 could not effectively adsorb at the interface to form a complete interfacial film. Emulsions stabilized by H-30, 50, and 70 showed the benign storage stability due to the formation of the strong interfacial film and network structure in emulsions. This study improved understanding about interfacial properties of cellulose nanoparticles with different lengths.

Microscale Interactions of Surfactant and Polymer Chemicals at Crude Oil/Water Interface for Enhanced Oil Recovery

Summary The conventional experimental techniques used for performance evaluation of enhanced oil recovery (EOR) chemicals, such as polymers and surfactants, have been mostly limited to bulk viscosity, phase behavior/interfacial tension (IFT), and thermal stability measurements. Furthermore, fundamental studies exploring the different microscale interactions instigated by the EOR chemicals at the crude oil/water interface are scanty. The objective of this experimental study is to fill this existing knowledge gap and deliver an important understanding on underlying interfacial sciences and their potential implications for oil recovery in chemical EOR. Different microscale interactions of EOR chemicals, at crude oil/water interface, were studied by using a suite of experimental techniques, including an interfacial shear rheometer, Langmuir trough, and coalescence time measurement apparatus at both ambient (23°C) and elevated (70°C) temperatures. The reservoir crude oil and high-salinity injection water (57,000 ppm total dissolved solids) were used. Two chemicals, an amphoteric surfactant (at 1,000 ppm) and a sulfonated polyacrylamide polymer (at 500 and 700 ppm) were chosen because they are tolerant to high-salinity and high-temperature conditions. Interfacial viscous and elastic moduli (viscoelasticity), interface pressures, interface compression energies, and coalescence time between crude oil droplets are the major experimental data measured. Interfacial shear rheology results showed that surfactant favorably reduced the viscoelasticity of crude oil/water interface by decreasing the elastic and viscous modulus and increasing the phase angle to soften the interfacial film. Polymers in brine either alone or together with surfactant increased the viscous and elastic modulus and decreased the phase angle at the oil/water interface, thereby contributing to interfacial film rigidity. Interfacial pressures with polymers remained almost in the same order of magnitude as the high-salinity brine. In contrast, a significant reduction in interfacial pressures with surfactant was observed. The interface compression energies indicated the same trend and were reduced by approximately two orders of magnitude when surfactant was added to the brine. The surfactant was also able to retain similar interface behavior under compression even in the presence of polymers. The coalescence times between crude oil droplets were increased by polymers, while they were substantially decreased by the surfactant. These consistent findings from different experimental techniques demonstrated the adverse interactions of polymers at the crude oil/water interface to result in more rigid films, while confirming the high efficiency of the surfactant to soften the interfacial film, promote the oil droplets coalescence, and mobilize substantial amounts of residual oil in chemical EOR. This experimental study, for the first time, characterized the microscale interactions of surfactant-polymer chemicals at the crude oil/water interface. The applicability of several interfacial experimental techniques has been demonstrated to successfully understand underlying interfacial sciences and oil mobilization mechanisms in chemical EOR. These techniques and methods can provide potential means to efficiently screen and optimize EOR chemical formulations for better oil recovery in both sandstone and carbonate reservoirs.

Functional properties of chickpea protein-pectin interfacial complex in buriti oil emulsions and spray dried microcapsules

The aim of the present study was to investigate the impact of chickpea protein (CP) alone or in the form of sequentially adsorbed chickpea protein and high methoxylated pectin (CP-HMP) on the microencapsulation of buriti oil by spray drying. CP was extracted and characterized by its molecular weight distribution, zeta potential and solubility. The adsorption of CP and CP-HMP complexes to the oil/water (O/W) interface was investigated by measurement of the interfacial tension. The interactions between the molecules at the O/W interface were analyzed by interfacial shear rheology. Emulsions containing CP or CP-HMP were prepared at pH 3.5, homogenized and spray dried at 180/70 °C and 210/90 °C (inlet/outlet) temperature. The oil droplet size distribution (ODS) of emulsions before and after spray drying, the encapsulation efficiency (EE) of microcapsules and their oxidative stability were evaluated. The interfacial tension of CP at the O/W interface was not affected by pectin addition. However, interfacial shear rheology revealed strong interactions between CP-HMP complexes, maintaining the physical integrity of emulsion oil droplets during spray drying. On the other hand, interactions in the CP film were weaker and the droplets were affected by spray drying, suffering from an increase in size. The EE of CP-HMP microcapsules was higher than for CP microcapsules, which suggests a synergistic effect. The spray drying temperature had no effect on the EE. During 6 months of storage, a slight increase of the conjugated dienes content was observed for all microcapsules. However, the type of microcapsule and the temperature of spray drying had no effect on the development of lipid oxidation.

Interfacial properties of ultrahigh methoxylated pectin

The interfacial properties of ultrahigh methoxylated pectin (UHMP) prepared via esterification of citrus pectin (CP) were investigated. The intrinsic viscosity ([η]) of pectin was significantly decreased from 1211.5 mL/g to 294.9 mL/g as the degree of methylation (DM) increased from 63.18 ± 0.08% to 91.52 ± 0.11%. Surface tension (γ) analysis indicated that UHMP had a critical micelle concentration (CMC) of 0.8 g/L, which was slightly smaller than that of sugar beet pectin (SBP) (1.0 g/L). The morphology of the UHMP aggregation presented a network structure and irregular clusters at 10 μg/mL and 1 μg/mL based on atomic force microscopy (AFM). Transmission electron microscopy (TEM) observations further confirmed the self-aggregation behaviours and rod-like micelles of UHMP. The surface excess (Γ) was 1.69 ± 0.17 μmol/m2 for UHMP, which was lower than the values of SBP (1.88 ± 0.21 μmol/m2) and CP (2.91 ± 0.57 μmol/m2). Correspondingly, UHMP possessed the highest molecular area (A) of 0.99 ± 0.10 nm2. Thus, UHMP was proposed to be more flexible and extendable at the interface. The interfacial shear rheology study suggested that UHMP was able to form an elastic-dominant interfacial film to stabilize the oil/water interface.

Conjugate microgel-stabilized Pickering emulsions: Role in delaying gastric digestion

In this study, a new class of microgels called ‘conjugate microgels’ was designed, where whey protein isolate (WPI) was conjugated with dextran (Dx, 500 kDa) (WPI-Dx) via Maillard reaction before fabricating the microgel particles. Such microgel particles were assessed for their abilities to act as Pickering stabilizers for oil-in-water emulsions and also checked if they offered gastric stability to the Pickering emulsions during in vitro digestion against interfacial pepsinolysis. WPI-Dx conjugates were obtained by controlled dry heating (60 °C, 79% RH, 24–48 h incubation). Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and ortho-phthaldialdehyde (OPA) profile revealed that the degree of conjugation ranged from 11.6 to 28.1%. The WPI-Dx conjugates were re-dispersed and heat-treated to form heat-set gels with moduli ranging from ~45 to 250 kPa. Microgel particles (hydrodynamic diameters of 130–150 nm, ζ-potentials of −4.5 to −8.0 mV) were created by controlled shearing of these heat-set gels. Interfacial shear rheology measurements and microscopic examination confirmed that conjugated microgel particles with lower degree of conjugation (WPDx10M) were effective as Pickering stabilizers. When present in an aqueous dispersion, WPDx10M had reduced degree of gastric proteolysis (120–130 μM free NH2) as compared to non-conjugated counterparts (187–205 μM free NH2). When present at the droplet surface, cross-correlation image analysis revealed that WPDx10M was successful in delaying interfacial gastric proteolysis. Insights from this study suggest that conjugate microgel particles might be useful to design gastric-stable Pickering emulsions in the future for effective delivery of lipophilic compounds to the intestines.

Rheological approaches as a tool for the development and stability behaviour of protein-stabilized emulsions

Emulsion stability is the primary requirement for the industrial applications of many commercial food products. This work analyses the importance of rheology on the characterisation of protein-adsorbed systems, from complex fluid-fluid interfaces to bulk emulsions, as well as their relationship to the stability behaviour of the final emulsion. To accomplish this aim, three case studies involving protein-adsorbed systems at different scales are discussed: bulk rheological properties of protein-stabilized emulsions, interfacial rheology of proteins adsorbed at O/W interface, and the links between interfacial and bulk rheology of proteins/polysaccharide mixtures. The knowledge of the interfacial behaviour on a nanoscale is essential for the development of optimal properties on both the microscale (droplet size distributions and microstructure) and the macroscale (bulk rheology and stability). This work presents linear and nonlinear rheology of complex interfaces, including a discussion on recent progress available for analysing and modelling nonlinear interfacial rheology data. In addition, a similar rheological analysis for protein-stabilized emulsions is reviewed, with the aim of exploring possible links between interfacial shear rheology and emulsion rheology, as well as their connections to emulsion microstructural parameters and emulsion stability. This approach, which mainly relies on the characterization of the interface, might be regarded as very useful to tailor interfaces for the development of optimal emulsion microstructure and stability.

Interfacial viscoelasticity and aging effect on droplet formation and breakup

Interfacial rheology of interfaces stabilized by food ingredients has been studied extensively within the limits of small and slow deformations, within the linear viscoelastic regime (LVR). However, in practice, products such as foams or emulsions undergo fast and large deformations during food processes such as chewing. emulsifying, or foaming. In this study, we used capillary break-up and droplet formation to observe and quantify large and fast deformations of such interfaces, in the presence of surface viscoelasticity. We studied the inertial thinning of the liquid neck during drop formation using high-speed imaging. We tested solutions of several surface active molecules, including two low molecular weight surfactants (SDS and Tween 20), two milk proteins (β-Lactoglobulin, Bovine Serum Albumin) and the saponin Escin. Escin showed the most significant effect on the shape of the neck and neck thinning dynamics. Interfacial shear rheology measurements indicated that the unusual breakup observation of Escin solutions was related to the high viscoelastic surface shear moduli. These high moduli, and the resulting more symmetric and shorter neck shape observed for the proteins and Escin, are associated with the formation of solid-like interfacial structures. However, the presence of a viscoelastic interface did not affect the inertial thinning regime, which indicates that the solid structures were broken down locally at the area of minimum radius (Rmin), and affected only the shape outside this region. The results of this work therefore, show that interfacial measurements within the LVR are not entirely representative for fast and large deformations well beyond linearity.

Effects of Oil Droplet Size and Interfacial Protein Film on the Properties of Fish Myofibrillar Protein-Oil Composite Gels.

The effects of oil droplet size and the formation of an interfacial protein film (IPF) on silver carp myofibrillar protein (MP)–oil composite gels were studied. MP- or Tween 80-stabilized camellia seed oil emulsions with different droplet sizes were prepared and added to MPs to prepare composite gels. The oil droplet size of the Tween 80-stabilized emulsion was significantly smaller (p < 0.05) than that of the MP-stabilized emulsion with the same homogenization speed. However, polymerization of Tween 80-stabilized emulsions during the preparation of the composite gels was found. Composite gels with the MP-stabilized emulsions of a small droplet size showed significantly improved water-holding capacity, texture, and dynamic rheological properties. Interfacial shear rheology studies revealed that the storage modulus (G’) of the MP-stabilized emulsion composite gels was higher than that of the Tween 80-stabilized gels, and the tan δ of the MP-stabilized oil emulsion composite gels was smaller than that of the Tween 80-stabilized gels, indicating that stronger elastic gel structures were formed. These results suggested that the IPF formed in the MP-stabilized emulsion helped stabilize the oil droplets embedded in the protein gel network, and the smaller the droplet size, the more stable the composite gel. This work provides a better understanding of how oil emulsions interact with protein and affect the properties of MP–oil composite gels.

Interfacial/foaming properties and antioxidant activity of a silkworm (Bombyx mori) pupae protein concentrate

The current consumer demand for healthier diets, the growing interest in the search for new sources of protein, and the desire to reduce the negative effects on the environment have increased interest in the study of insect proteins. The present study focused on the technofunctional characteristics (interfacial and foaming properties) and the in-vitro antioxidant activity of a protein concentrate obtained from silkworm (Bombyx mori) pupae (SPC). The isoelectric point of the SPC was close to pH 4.0–5.0 as determined by protein solubility and z potential analysis. Given that the SPC had solubilities of ~50% and z potentials of ~20 mV at pH 2.0 and 8.0, it was decided to further study SPC properties at these pH values.The supernatant obtained after adjustment of SPC to pH 8.0 showed higher (p < 0.05) antioxidant activity than that at pH 2.0 when analysed by the ferric reducing antioxidant power (FRAP) assay (168.0 ± 3.0 V. 43.5 ± 8.1 μmol Trolox Eq. ·g−1 protein). However, no significant differences in antioxidant activity were found between pH 2.0 and 8.0 when using the oxygen radical absorbance capacity (ORAC) assay (1826.0 ± 131.9 vs. 1659.2 ± 46.8 μmol Trolox Eq. g−1 protein). The interfacial properties of SPC were determined at pH 2.0 and 8.0 during protein adsorption and after reaching the pseudo equilibrium state by means of dilatational and interfacial shear rheology following by foaming capacity and stability analyses. Faster adsorption kinetic values were obtained at pH 8 (kD∗=69.2±0.4 Vs. 29.5±0.9mN/m·s−1/2at pH 2.0). However, lower kinetic values at pH 2.0 increased the elastic behaviour of the viscoelastic interfacial film formed (E's ⁓ 30 mN/m at pH 2.0 V. E's ⁓ 20 mN/m at pH 8.0), which can be related with the higher protein sizes found at pH 2.0. These rearrangements of the SPC components appeared to increase its foaming capacity, whereas the foaming capacity of SPC adjusted to pH 8.0 was minimal.

Multiscale Aqueous-Ion Interactions at Interfaces for Enhanced Understanding of Controlled-Ionic-Composition-Waterflooding Processes in Carbonates

SummaryIn this study, we summarize and discuss the data reported from a series of multiscale experiments to explore the interactions of salinity and aqueous ions at fluid/fluid and rock/fluid interfaces and to understand the pore-scale oil-recovery mechanisms in controlled-ionic-composition waterflooding (CICW). Experimental data on various crude-oil/brine/carbonate and crude oil/brine physicochemical changes/effects at elevated temperatures were obtained using a variety of static and dynamic techniques at different scales ranging through atomic/molecular/macroscopic scales. The techniques include surface-force apparatus (SFA), cryo-broad-ion-beam scanning electron microscope (BIB-SEM), zeta-potentials, microscope-based oil liberation, macroscopic contact angles, interfacial shear rheology, and integrated thin-film drainage apparatus (ITFDA). The salinities of brines were varied from zero-salinity deionized (DI) water to higher-salinity injection water in addition to changing the individual ion compositions.The integration of results obtained from different multiscale experiments showed that both salinity and individual aqueous ions play a major role not only in determining the oil release from the rock surface owing to the interactions at the rock/fluid interface but also in impacting released oil-ganglion dynamics for efficient oil mobilization through the interactions at the fluid/fluid interface. The key findings can be summarized as follows: (1) at zero salinity, unfavorably much higher adhesion and stronger rigid films to adversely impact crude-oil-droplet coalescence were observed at rock/fluid and fluid/fluid interfaces, respectively; (2) an optimal lower salinity containing a sufficient amount of sulfate ions is necessary to cause nanoscale ion exchange at the rock/fluid interface that changes the surface charge/potential to favorably alter adhesion and microscopic contact angles for efficient oil release from the rock surface; and (3) an adequate salinity containing higher amounts of magnesium and calcium ions is desired to form less-rigid films at the fluid/fluid interface that promote the coalescence of released oil ganglia for effective mobilization. On the basis of these novel findings, controlled-ionic-composition water can be defined as a tailored water containing certain salinity and selective composition of three key ions including: sulfates, magnesium, and calcium. It must contain lower amounts of monovalent ions and should have the right balance of the three key ions to enable favorable interactions at both fluid/fluid and rock/fluid interfaces in carbonates. The novelty of this work is that it systematically analyzes and consolidates all the multiscale (atomic/molecular/macroscopic scales) experimental data obtained using rock and crude-oil samples from the same carbonate reservoir. Also, consistent trends were identified from different experimental techniques at both rock/fluid and fluid/fluid interfaces to establish a clear connection among multiscales and subsequently understand the causative pore-scale mechanisms responsible for oil recovery in CICW processes. In other words, this work has successfully transmitted the physics behind individual mechanisms and their interplay through different length scales to directly address one of the key open questions raised by Bartels et al. (2019).The analysis on multiscale aqueous-ion interactions at the two interfaces performed in this study resulted in the major finding that the controlled-ionic-composition water effect in carbonates is a combination of two effects, one being related to the release of oil attached on rock surfaces (wettability change) and the other being related to improved oil-phase connectivity and better oil mobilization (enhanced coalescence of oil ganglia). It also highlighted the important learning point that not every low-salinity water can become a controlled-ionic-composition water for carbonates. These new learnings and the novel knowledge gained provide useful practical guidelines on how to design optimal injection-water chemistries for waterflooding projects in carbonate reservoirs.

Molecularly Designed Interfacial Viscoelasticity by Dendronized Polymers: From Flexible Macromolecules to Colloidal Objects.

The thermodynamic and rheological properties of densely packed dendronized polymers (DPs) at water-air interfaces were studied here for first- and fourth-generation DPs (PG1, PG4) with both small (Pn ≈ 50) and large (Pn ≈ 500) backbone degrees of polymerization. The excellent control over the structural characteristics of these polymers enabled us to investigate how the interfacial properties change as we go from thin, flexible macromolecules toward thicker molecular objects that display colloidal features. The effects of the dendron generation, affecting the persistence length, as well as the degree of polymerization and surface pressure on the formation of DP layers at the water-air interface were studied. Surface pressure measurements and interfacial rheology suggest the existence of significant attractive interactions between the molecules of the higher generation DPs. While all DPs featured reproducible Π-A diagrams, successive compression-expansion cycles and surface pressure relaxation experiments revealed differences in the stability of the formed films, which are consistent with the variations in shape persistence and interactions between the studied DPs. Atomic force microscopy after Langmuir-Blodgett transfer of the films displayed a nanostructuring that can be attributed to the increase in attractive forces with increasing polymer generation and anisotropy. The importance of such structures on the surface properties was probed by interfacial shear rheology, which validated the existence of strong albeit brittle structures for fourth-generation DPs. Ultimately, we demonstrate how in particular rod-like DPs can be used as robust foam stabilizers.

Mechanical Properties of Solidifying Assemblies of Nanoparticle Surfactants at the Oil-Water Interface.

The effect of polymer surfactant structure and concentration on the self-assembly, mechanical properties, and solidification of nanoparticle surfactants (NPSs) at the oil-water interface was studied. The surface tension of the oil-water interface was found to depend strongly on the choice of the polymer surfactant used to assemble the NPSs, with polymer surfactants bearing multiple polar groups being the most effective at reducing interfacial tension and driving the NPS assembly. By contrast, only small variations in the shear modulus of the system were observed, suggesting that it is determined largely by particle density. In the presence of polymer surfactants bearing multiple functional groups, NPS assemblies on pendant drop surfaces were observed to spontaneously solidify above a critical polymer surfactant concentration. Interfacial solidification accelerated rapidly as polymer surfactant concentration was increased. On long timescales after solidification, pendant drop interfaces were observed to spontaneously wrinkle at sufficiently low surface tensions (approximately 5 mN m-1). Interfacial shear rheology of the NPS assemblies was elastic-dominated, with the shear modulus ranging from 0.1 to 1 N m-1, comparable to values obtained for nanoparticle monolayers elsewhere. Our work paves the way for the development of designer, multicomponent oil-water interfaces with well-defined mechanical, structural, and functional properties.