Surface Dilatational Modulus Research Articles

Hyaluronic acid-decorated lipid nanocarriers as novel vehicles for curcumin: Improved stability, cellular absorption, and anti-inflammatory effects

This study aimed to investigate how hyaluronic acid interfacial decoration affects the stability, cellular absorption, and anti-inflammatory effects of curcumin-loaded nanostructured lipid carriers. Nanocarriers were synthesized with an ovalbumin single layer and ovalbumin/hyaluronic acid double, mixed, or conjugated layers. All nanocarriers were spherical (200–300 nm diameter), and their encapsulation efficiency exceeded 95 %. Among the layers, the conjugated one exhibited the highest elastic surface dilatational modulus of approximately 40 mN/m, and the longest curcumin half-life of 186.07 days at 4 °C. Spearman's correlation analysis showed a negative correlation (r = −0.6698) between the recrystallization index and curcumin stability. The layer's mechanical strength improved curcumin stability by preventing crystal transition. Hyaluronic acid decoration enhanced the curcumin uptake of Caco-2 cells by 1.96–2.48 folds. Among the layers, the conjugate one was the most effective because of its strong binding constant with the receptor. Hyaluronic acid decoration improved the anti-inflammatory effects of curcumin.

Research on compound amidohydroxysulfobetaine foamer for high-temperature and high-salinity clastic reservoirs

A high-quality foaming agent should exhibit excellent solubility in formation water and strong foaming ability, while also meeting the requirements of stability under high-temperature and high-salinity conditions, as well as low adsorption capacity. This study explores the potential of amidohydroxysulfobetaine surfactant as a foaming agent in sandstone reservoirs under specific reservoir conditions of 110 ℃ and 25.0×104 mg/L salinity. The findings indicate that compounding EHSB with a small amount of LHSB to form LA13 significantly reduces the Krafft point of EHSB. Furthermore, LA13 demonstrates outstanding solubility in 25.0×104 mg/L brine and exhibits an overall adsorption capacity on quartz sand surfaces lower than 0.6 mg/g when its concentration is below 1.0 wt%. Performance evaluation of bulk foam for LA31 at concentrations ranging from 0.05 wt% to 0.4 wt% suggests that using a foaming agent concentration of 0.05 wt% results in relatively low foaming volume and foam decay half-life; however, consistent foaming performance is observed across other concentrations, leading to highly stable foam due to the compound system's higher surface dilational modulus being the primary factor contributing to foam stability. Flow experiments reveal that the foam generated in cores with permeabilities of 46.5 mD, 185.5 mD, 632.0 mD, and 2005.3 mD exhibits a high resistance factor when the concentration of LA13 exceeds 0.1 wt%, while also demonstrating commendable gas-channeling regulation capability. Therefore, it is recommended to use LA13 as a foaming agent for field applications when its concentration surpasses 0.1 wt%. Additionally, comparing the mobility of foam formed by concentrations of 0.1 wt% and 0.2 wt% LA13 in cores with varying permeabilities shows that LA13 exhibits selective mobility regulation specifically in cores with permeabilities lower than 632.0 mD.

Hydroxysulfobetaine foamer for potential mobility control application in high-temperature and ultra-high salt reservoirs

A good foamer should have good solubility in the formation of water, strong foaming ability, and also meet the requirements of thermal stability and low adsorption capacity under high temperature and high salinity conditions. The foam properties of hydroxylsulfobetaine surfactant with different carbon chain lengths were measured at 130 °C, 30 MPa, and in brine with a salinity of 22 × 104 mg·L−1. The results showed that hydroxylsulfobetaine surfactant with long carbon chains exhibited strong foam stability, with foam decay half-lives reaching 13 days for 0.4 wt% EHSB (erucamide propyl hydroxysulfobetaine) and 2.9 days for 0.4 wt% HSB18 (octadecyl dimethyl hydroxypropyl sulfobetaine), respectively. Hydroxysulfobetaine surfactant with short carbon chains had a foam decay half-life of less than 10 h. Considering the poor thermal stability of EHSB at 130 °C, HSB18 was primarily chosen as the foamer. HSB18 and HSB12 (dodecyl dimethyl hydroxypropyl sulfobetaine) were combined in a ratio of 3:1 to form the compound hydroxysulfobetaine MHSB31, which demonstrated good solubility in saline solution with KP (Krafft point) lower than 30 °C. The evaluation, using different concentrations of MHSB31, showed that the foam decay half-life ranged from 88 h for 0.03 wt% MHSB31 compared to 42 h for 0.1 wt% MHSB31. The excellent foaming performance of the compound system is attributed to its high surface dilational modulus and the formation of wormlike micelles. The adsorption capacity test demonstrated that when the concentration was less than 1 wt%, the adsorption capacity of MHSB31 on quartz sand surface was less than 1 mg·g−1, satisfying oilfield requirements. The results of the flow experiment at 130 °C and 10 MPa, in brine with a salinity of 22 × 104 mg·L−1, show that when the concentration of MHSB31 is greater than 0.1 wt%, the foam formed in the core with permeability of 632 mD and 2005 mD has a higher apparent viscosity and resistance factor. Additionally, the relative mobility of the foam formed in the core with a permeability of 2005 mD is lower than that formed in the core with a permeability of 632 mD. This indicates a certain selective reduction effect on mobility. Due to the influence of ultimate capillary pressure, both foam resistance factor and apparent viscosity are lower for the 47 mD core injected with different concentrations of MHSB31 ranging from 0.05 wt% to 0.5 wt%. The evaluation data presented in this paper regarding bulk foam and flow foam, using hydroxysulfobetaine surfactant under high temperature, high pressure, and high salinity conditions, have significant guiding significance for selecting and applying foamers in reservoirs with such harsh conditions.

Adsorption Layer Properties and Foam Behavior of Aqueous Solutions of Whey Protein Isolate (WPI) Modified by Vacuum Cold Plasma (VCP)

For years, cold plasma processing has been used as a non-thermal technology in industries such as food. As interfacial properties of protein play a remarkable role in many processes, this study investigates the effect of cold plasma on the foaming and interfacial behavior of WPI. The objective of this study is to evaluate the effect of different gases (air, 1:1 argon–air mixture, and sulfur hexafluoride (SF6)) used in low-pressure cold plasma (VCP) treatments of whey protein isolate (WPI) on the surface and foaming behavior of aqueous WPI solutions. Dynamic surface dilational elasticity, surface tension isotherms, surface layer thickness, and the foamability and foam stability were investigated in this study. VCP treatment did not significantly affect the adsorption layer thickness. However, an increase in induction time, surface pressure equilibrium value, and aggregated size is observed after SF6VCP treatment, which can be attributed to the reaction of WPI with the reactive SF6 species of the cold plasma. The surface dilational elastic modulus increased after VCP treatment, which can be related to the increased mechanical strength of the protein layer via sulfonation and aggregate formation. VCP treatment of WPI increases the foam stability, while the average diameter of foam bubbles and liquid drainage in the foam depends on the gas used for the cold plasma.

Comparative study on the foam and air-water interface properties of ethanol-soluble and non-ethanol components in wheat aqueous phase protein

We conducted an investigation into the foam and interface properties of wheat aqueous phase protein (WAP) along with its ethanol-soluble fraction (ES) and non-ethanol-soluble fraction (NES). The results reveal that the ES component exhibits exceptional foamability at both pH 5 and 7, whereas the NES component demonstrates relatively lower foamability but excels in foam stability at pH 5 and 7. The ES component shows a higher initial surface pressure, indicating stronger surface activity and, consequently, superior foamability. In contrast, the NES component exhibits a faster adsorption rate. The surface dilatational modulus of all three proteins increases over time and with varying frequencies, forming an interface layer primarily characterized by elastic behavior. Notably, the NES component displays heightened sensitivity to oscillations, suggesting its enhanced capacity to form a stable adsorption layer at the interface, thereby contributing to foam stability. Within WAP, the combined interactions of the ES and NES components dictate its foam properties, with the ES component primarily influencing foamability and the NES component playing a more significant role in foam stability. This study offers valuable insights into the intricate behavior of wheat proteins at gas-liquid interfaces, thereby enhancing our comprehension of the formation and stability mechanisms of dough aqueous phase foams.

A comparison of surface properties for bovine serum albumin and human serum albumin – Dynamic/equilibrium surface tension and dilational modulus

The biological functionalities of Human Serum Albumin (HSA) and Bovine Serum Albumin (BSA) have been extensively studied in the literature. However, limited information is available on their surface properties [dynamic/equilibrium surface tension (ST) and dilational modulus (E)]. This study compared the dynamic/equilibrium ST of HSA and BSA solutions and the E of the adsorbed films. A pendant bubble tensiometer was employed for measuring the relaxations of ST of HSA/BSA solutions at C = 0.01 – 90 (10−10 mol/cm3). The data revealed that while the dynamic ST of HSA(aq) and BSA(aq) exhibited a similar relaxation in general, the ST of HSA(aq) relaxed notably faster at the post-induction regime than BSA(aq). The equilibrium ST of both HSA and BSA was constant at 52.6 and 52.3 mN/m over a wide concentration range, C = 0.01 – 90 (10−10 mol/cm3). The E of HSA and BSA films exhibited a near-identical concentration dependency to each other: E was reasonably constant at ∼ 21 mN/m from C = 0.05 to 0.2 (10−10 mol/cm3), and at further concentration elevations, E rose notably, and eventually leveled off at ∼ 52 and ∼ 45 mN/m for HSA and BSA films, respectively.

Solvent Quality and Aggregation State of Asphaltenes on Interfacial Mechanics and Jamming Behavior at the Oil/Water Interface.

The formation of highly stable water-in-oil emulsions results in complications in both upstream and downstream processing. Emulsion stability in these systems has been connected to the adsorption of surface-active asphaltenes that are assumed to form a rigidified film at the oil/water (o/w) interface. Full characterization of this behavior is needed to allow for engineered solutions for enhanced oil recovery. Interfacial properties, such as surface pressure and interfacial elasticity, are implicated in the stabilizing mechanism for these observed films. Asphaltenes are known to be interfacially active in both good solvents (aromatics) and poor solvents (high ratio of aliphatic to aromatic). However, due to inherent complexities present in asphaltene studies, the details of the mechanical properties of the interface remain poorly understood. Despite the widely accepted perception that asphaltenes form persistent rigid films at fluid-fluid interfaces, the connection between bulk solution properties and interfacial mechanics has not been resolved. Here, the effects of solvent quality on the interfacial properties of asphaltene dispersions are determined by using a well-defined asphaltene/solvent system. Interfacial rigidity is observed only under poor solvent conditions, while the good solvent system remains fluid-like. The interfacial rheology under good and poor solvent conditions is measured simultaneously with surface pressure measurements to track interfacial development. It is shown that surface pressure and dilatational modulus measurements are not indicators of whether an interface demonstrates rigid behavior under large compressions. Finally, conditions required for asphaltene-coated interfaces to exhibit the mechanical behavior associated with a rigidified interface are defined. This work provides a framework for quantifying the impact of the aggregation state of asphaltenes on the stability and mechanics at the o/w interface.

Continuous enzyme crosslinking modifying colloidal particle characteristics and interface properties of rice bran protein to improve the foaming properties

The improvement of rice bran protein (RBP) foaming properties by continuous Transglutaminase (TGase) enzymatic cross-linking was studied and the related mechanism was analyzed. Under the conditions of enzyme addition of 0.5 kat/kg of protein and 3 h of enzyme crosslinking time, the foam capacity value and foam volume ratio of BPR were increased to 375% and 79.45% respectively and the liquid drainage rate of RBP samples foam system was decreased. Particle size distribution, zeta potential and surface hydrophobicity indicated that TGase treatment has changed the surface properties and aggregation state of RBP affecting the adsorption of TGase treated RBP on the interface. Meanwhile circular dichroism and intrinsic fluorescence suggested that TGase treatment made the tertiary structure of RBP aggregation more compact. The behavior of the air-water interface revealed that compared to native RBP, TGase cross-linked RBP exhibited a faster and more complex adsorption process, and a higher surface dilatational modulus. Enzyme cross-linked RBP particles mainly stabilized the interfacial membrane by Pickering mechanism, and TGase could catalyze cross-linking of RBP at the interface to enhance the elastic modulus of the interface. This study provides theoretical support for application of protein particles prepared by TGase enzymatic cross-linking in foamed foods.

Air-water interfacial and foaming properties of native protein in aqueous quinoa (Chenopodium quinoa Willd.) extracts: Impact of pH- and heat-induced aggregation

The shift from animal-based towards more sustainable plant-based food systems has increased the interest in leguminous protein such as that from the pseudo-cereal quinoa. In spite of the importance of foaming agents in a wide variety of food systems, the foaming properties of quinoa protein are still poorly understood. In this research paper, the air-water (A-W) interfacial and foaming properties of aqueous extracts from defatted quinoa wholemeal were investigated. Foams contained both albumins and 11S globulins, but no 7S globulins, despite the presence of the latter proteins in the extracts. At pH 7.0, both albumins and 11S globulins were soluble and jointly adsorbed at the A-W interface. Closer to the 11S globulin isoelectric point (pH 5.0), only albumins adsorbed at the A-W interface. Cultivar-dependent differences in protein composition and functionality allowed to hypothesize that 11S globulins foam better when present as dissociated acidic and basic subunits rather than as monomers. Heat-induced aggregation of 11S globulins led to enrichment of albumins at the A-W interface. This was associated with an increased surface tension and a decreased surface dilatational modulus. Presumably, quinoa albumins have low tendency to interact at the A-W interface resulting in a weakly elastic interfacial network. At the same time, globulin aggregates formed during heating at pH 5.0 and 7.0 lead to unstable and stable foams, respectively. As protein functional properties are important for the quality of many food products, these insights are valuable when developing novel quinoa-based food products requiring interfacial stability.

Effect of surfactants and interfacial rheology on equilibrium drop size in turbulent liquid-liquid dispersions

Surfactants are often required to stabilize liquid-liquid dispersions produced by high shear mixers. Due to the high power input, drops are deformed rapidly in the dispersion zone so the dynamic interfacial properties governed by the surfactant adsorption rate can have a significant impact on the resulting drop size. The objective of this work is to develop a fundamental link between surfactant adsorption dynamics, interfacial properties, and turbulent emulsification processes. To ensure constant bulk surfactant concentration during dispersion, equilibrium drop size for dilute dispersions produced by a batch rotor-stator mixer were studied. Silicone oils of various viscosity were dispersed in aqueous nonionic surfactant solutions. Drop size distributions (DSD) were measured via a video microscopy/automated image analysis technique. Equilibrium interfacial tension was measured via a pendant drop technique, as a function of surfactant concentration. The dynamic surface tension was similarly measured. The data were fit to the Langmuir adsorption isotherm and the long-times approximation to the Ward – Tordai equation and the adsorption parameters and surfactant diffusivities so obtained were employed, with an estimate of the drop deformation timescale, to estimate the surface dilational modulus (Esd) or Marangoni stress acting on the drop’ surface due to interfacial tension gradients. Trends observed in the measured equilibrium mean drop size and DSD are explained in terms of the interfacial and rheological properties. Below the CMC, Esd peaks and the drop size increases with bulk surfactant concentration, despite a decrease in equilibrium interfacial tension. Above the CMC, Marangoni stresses are small but the presence of the surfactant still modifies the rheology of the interface, increasing the effective viscosity of the drops. A comprehensive set of mechanistic models for drop size in turbulent flows, based on Kolmogorov-Hinze theory, was developed and modified to partially account for the effect of surfactants via an appropriately defined effective viscosity. The approach allows integration of surfactant phenomena into widely accepted correlations for drop size in surfactant free systems.

Self-assembly of plant polyphenols-grafted soy proteins to manufacture a highly stable antioxidative Pickering emulsion gel for direct-ink-write 3D printing

The practicable application of 3D printing in the pharmaceutical and food sectors directly relates to the preparation of highly stable bioactive printable inks. Here, three different polyphenols (rosemary polyphenols, thyme polyphenols, and basil polyphenols) were individually grafted onto soy protein isolate through a free-radical grafting method to produce a precursor printable ink to develop 3D printed plant-based cheese. The morphological features, emulsion rheology measurements, quartz crystal microbalance with dissipation monitoring techniques, and interfacial shear rheology were used to monitor emulsification features and interfacial rheology (i.e., adsorption kinetics, viscoelastic features, and interfacial adsorbed layers) of precursor inks. Compared to soy-based ink, polyphenols-grafted soy protein inks developed more stable emulsions against coalescence with finer droplets. Also, the interfacial adsorption properties of protein particles were improved after the grafting process, in which the surface dilatational viscoelastic moduli and interfacial pressure were boosted. The ink formulating by soy protein-g-rosemary polyphenols (with greater hydrophobicity) showed a emulsion droplets with smaller size, had a stiffer structure, and stronger surface activity than inks containing soy protein-g-thyme or soy protein-g-basil polyphenols, which displayed a 3D printed cheese analogue with improved lubrication property, higher creamy sensation and mouth-coating feature. Overall, this work suggests that compatibilization of the plant polyphenols and the soy proteins offers an opportunity for adopting plant-based inks in the 3D printing of advanced materials.

Air-water interfacial properties and quantitative description of pea protein isolate-Tween 20

The air-water interfacial properties of pea protein isolate (PPI) and Tween 20 (T20) were investigated in this study. The result of dynamic foam analyzer showed that the foam prepared by 0.5%PPI-0.1%T20 exhibited higher foam stability at 30 min and uniform bubble size distribution. The protein displacement by Tween 20 at the air-water interface was observed by atomic force microscopy (AFM) through the imaging of Langmuir-Blodgett (LB) films. During the displacement of pea protein isolate by the nonionic surfactant Tween 20, the surface pressure was increased while the complex surface dilatational modulus was decreased. Based on the AFM observations of the LB films, the quantitative analysis indicated the increased protein quantity in the foam network. To be emphasized, the formation of protein network at the plateau border of foams contributed to the increased foam stability. The AFM results showed that the protein at the air-water interface could be replaced by T20, but comparing with the PPI-stabilized foam, the addition of 0.1% T20 could increase the relative quantity of vicilin, thus leading to the increase of interconnected protein network at foam film to improve the foam stability. The research could promote the understanding of protein displacement by Tween 20 at the air-water interface, which could improve the quality of protein-surfactant stabilized foam-based foods.

Dilatational and shear rheology of soluble and insoluble monolayers with a Langmuir trough

HypothesisThe surface dilatational and shear moduli of surfactant and protein interfacial layers can be derived from surface pressures measured with a Wilhelmy plate parallel, ΔΠpar and perpendicular ΔΠperp to the barriers in a Langmuir trough. ExperimentalApplying area oscillations, A0+ ΔAeiωt, in a rectangular Langmuir trough induces changes in surface pressure, ΔΠpar and ΔΠperp for monolayers of soluble palmitoyl-lysophosphatidylcholine (LysoPC), insoluble dipalmitoylphosphatidylcholine (DPPC), and the protein β-lactoglobulin to evaluate Es∗+Gs∗=A0ΔΠparΔA and Es∗-Gs∗=A0ΔΠperpΔA. Gs∗ was independently measured with a double-wall ring apparatus (DWR) and Es∗ by area oscillations of hemispherical bubbles in a capillary pressure microtensiometer (CPM) and the results were compared to the trough measurements. FindingsFor LysoPC and DPPC, A0ΔΠparΔA≅A0ΔΠperpΔA meaning Es∗≫Gs∗ and Es∗≅A0ΔΠparΔA≅A0ΔΠperpΔA. Trough values for Es∗ were quantitatively similar to CPM when corrected for interfacial curvature. DWR showed G∗ was 4 orders of magnitude smaller than Es∗ for both LysoPC and DPPC. For β-lactoglobulin films, A0ΔΠparΔA>A0ΔΠperpΔA and Es∗ and Gs∗ were in qualitative agreement with independent CPM and DWR measurements. For β-lactoglobulin, both Es∗ and Gs∗ varied with film age and history on the trough, suggesting the evolution of the protein structure.

Effect of surfactant types on the foam stability of multiwalled carbon nanotube stabilized foam

Multiwalled Carbon nanotube (MWCNT) serves as one of emerging and attractive materials for stabilizing foams due to its small size, special surface property and rod-like structure. The combination of MWCNT and surfactant has been regarded as an effective strategy to improve foam stability in porous media. However, the effects of surfactant types on the dispersity of MWCNT and on the stability of MWCNT stabilized foams have yet to be clearly understood. More importantly, the lack of comprehensive study of the synergistic interactions between surfactants and MWCNTs seriously limits the understanding of MWCNT’s foam-stabilizing mechanism, restricting its application as the foam stabilizer. Herein, this paper aims to systematically study the foam-stabilizing performance and mechanism of different surfactant/MWCNT foam systems. Combining with the experimental results obtained from ultraviolet and visible spectrophotometry and zeta potential tests, environmental scanning electron microscope analyses, contact angle measurements, optical microscope observations, and surface tension and dilational viscoelastic modulus determinations, the foam-stabilizing mechanism of different surfactant/MWCNT foam systems can be conjectured as follows. Compared with anionic and nonionic surfactants (SDS and OP-10) modified MWCNT, the MWCNT modified by the cationic surfactant (CTAB) can yield better dispersity due to the larger electrostatic repulsion and higher steric resistance between MWCNTs after the adsorption of CTAB. The highly dispersed MWCNTs have small sizes, which make them enter the foam film easily and tend to aggregate at Plateau border. These aggregations can significantly slow down the film drainage. In addition, MWCNTs can improve the viscosity of foam film, which helps to increase the resistance of gas diffusion and mitigate bubble coalescence. After being adsorbed by surfactants, the modified MWCNT can adsorb on the air-water interface. Due to the higher detachment energy, the CTAB modified MWCNT has a stronger adsorption capacity at the air-water interface compared with SDS and OP-10 modified ones. This tight adsorption can improve the dilational viscoelastic modulus and thus enhance foam stability. Finally, the dual-sand pack experiments proved that the CTAB/MWCNT stabilized foams have good potential for conformance control in heterogenous reservoirs.

Dual-Grafting of Microcrystalline Cellulose by Tea Polyphenols and Cationic ε-Polylysine to Tailor a Structured Antimicrobial Soy-Based Emulsion for 3D Printing

An imperative processing way to produce 3D printed structures with enhanced multifunctional properties is printing inks in the form of a gel-like colloidal emulsion. The surface-modified microcrystalline cellulose (MCC) is an excipient of outstanding merit as a particulate emulsifier to manufacture a stable Pickering emulsion gel. The tuning of the MCC structure by cationic antimicrobial compounds, such as ε-polylysine (ε-PL), can offer a surface activity with an antimicrobial effect. However, the MCC/ε-PL lacks the appropriate emulsifying ability due to the development of electrostatic complexes. To overcome this challenge, (i) a surface-active MCC conjugate was synthesized by a sustainable dual-grafting technique (ii) to produce a highly stable therapeutic soy-based Pickering emulsion gel (iii) for potential application in 3D printing. In this regard, the tea polyphenols were initially introduced into MCC by the free-radical grafting method to decrease the charge density of anionic MCC. Then, the antioxidative MCC-g-tea polyphenols were reacted by ε-PL to produce a dual-grafted therapeutic MCC conjugate (micro-biosurfactant), stabilizing the soy-based emulsion system. The results indicated that the dual-grafted micro-biosurfactant formed a viscoelastic and thixotropic soy-based emulsion gel with reduced droplet size and long-term stability. Besides, there was an improvement in the interfacial adsorption features of soy–protein particles after micro-biosurfactant incorporation, where the interfacial pressure and surface dilatational viscoelastic moduli were enhanced. Consequently, it was revealed that the therapeutic Pickering emulsion gel was more suitable to manufacture a well-defined 3D architecture with high resolution and retained permanent deformation after unloading (i.e., a recoverable matrix). This work established that the modification of the MCC backbone by tea polyphenols and ε-PL advances its bioactive properties and emulsifying performance, which finally obtains a soy-based 3D printed structure with noteworthy mechanical strength.

Insight into the oil polarity impact on interfacial properties of myofibrillar protein

The interfacial behaviour of myofibrillar protein is critical to the stability of myofibrillar protein-stabilized oil in water emulsions. However, the effect of oil phase on the interfacial behaviour of myofibrillar protein and the resultant emulsion properties has not been widely analyzed. Therefore, this study was focused on exploring the relationship among oil polarity, the interfacial behaviour of myofibrillar protein and the emulsion physical stability. The results suggested that the surface load, interfacial pressure, diffusion rate, rearrangement rate and dilatational elastic modulus increased with the oil polarity decreasing. This was attributed to the larger extent of myofibrillar protein unfolding on the apolar interfaces which promoted the exposure of hydrophobic groups, leading to an increased protein-oil and protein-protein intermolecular interactions on the interface. However, the oil polarity barely affects the secondary structure of interfacial myofibrillar protein. Intriguingly, the emulsion physical stability was improved with the oil polarity increasing in a certain range despite the impaired viscoelasticity of interfacial film, possibly due to the lower interfacial tension of polar oils. A further increase in polarity exceeding the certain range contrarily reduced the emulsion stability, potentially due to the desorption and collapse of interfacial film. Our results demonstrated that oil polarity and mechanical strength of interfacial film should both be taken into consideration when studying emulsion stability. This knowledge could provide an in-depth understanding to reveal the underlying mechanism of how oil polarity affecting the interfacial behaviour of proteins and consequently the physical stability of the corresponding emulsions.

Stable foam systems for improving oil recovery under high-temperature and high-salt reservoir conditions

Foams have high apparent viscosity when flowing in porous media, therefore foam flooding could significantly improve unfavorable mobility ratios, increase sweep efficiency, and enhance oil recovery. However, the applications of foam flooding in high-temperature and high-salt reservoirs are seriously restricted as foam systems often have inferior foamability and stability in these reservoirs. In this study, to improve foam flooding effectiveness in high-temperature and high-salt reservoirs, novel foam systems with excellent stability and plugging capacity are developed by combining surfactants, additives, and polymers. The performance of bulk foam, physical properties of the solutions, and properties of foam systems in core-flow experiments are investigated to determine the synergistic effects among the components of the foam systems and their foamability and plugging effect in cores. In foam systems with sodium alcohol ether sulfate (AES) and dodecylhydroxypropyl sulfobetaine (DHSB) as surfactants, and dodecanol as additive, the combination of the components makes surface tension decreased and surface dilatational modulus increased, therefore the foamability and stability of the systems are improved. The results of core-flow experiments under high-temperature and high-salt conditions show that these combined systems require low injection rate for foam generation in reservoirs, which is beneficial for foam regeneration in reservoirs. Moreover, to further improve the foam performance, a hydrophobically associating water-soluble polymer (HAWP) is employed. The interactions between HAWP and the surfactants reduce the critical association concentration of HAWP, and result in the increase of solution apparent viscosity and foam stability. The results of core-flow experiments under high-temperature and high-salt conditions show that polymer-enhanced foam systems could significantly increase the sealing pressure, widen the sealing permeability range, and deal with the gas-channeling problem of foam flooding. These foam systems could provide a potential technical pathway for improving the effectiveness of foam flooding in high-temperature and high-salt reservoirs.

Microbial transglutaminase induced modification of wheat gliadin based nanoparticles and its impact on their air-water interfacial properties

There is a growing interest in plant protein based nanoparticles (NPs) such as wheat gliadin NPs (GNPs) for stabilizing foams in food systems. To increase the range of their applications, it is necessary to understand the role of different gliadin types and to tailor their behavior at air-water (A-W) interfaces. The latter is here done by modifying GNPs with microbial transglutaminase (TG). The most pronounced solubility loss of ω-gliadins (by 36.1%) after TG treatment at pH 4.5, measured by reversed phase high performance liquid chromatography (RP-HPLC), indicated that this protein type was more susceptible to TG action than α-gliadins and γ-gliadins, the solubility losses of which were 11.2 and 11.4% respectively. The lack of intramolecular disulfide bonds in ω-gliadins but not in the other gliadin types likely resulted in a greater accessibility of the lysine residues and thus more pronounced susceptibility of ω-gliadins to the enzyme. Interestingly, TG treatment of GNPs notably improved their foaming properties at pH 4.5 (and thus below the gliadin pI). The high surface dilatational modulus value of TG treated GNPs, when compared to control GNPs (53.9 and 32.7 mN/m, respectively), indicated formation of a strong viscoelastic A-W interfacial protein film, presumably due to the presence of TG catalyzed intermolecular isopeptide bonds. Fractionation of foams stabilized by (un-)treated GNPs and subsequent RP-HPLC analysis of the foam and liquid fractions showed that γ-gliadins were more important for A-W interface stability than ω-gliadins even if the latter were most affected by the TG treatment. Elimination of positively charged (at pH 4.5) lysine residues and conformational changes (both as a result of TG treatment) may have altered the ability of ω-gliadins to adsorb at the interface and to interact with other proteins thereat. Overall, TG treatment of GNPs resulted in formation of very strong protein films at the A-W interface stabilized by both covalent bonds and non-covalent interactions which in turn led to highly stable foams.

Interfacial rheology of sodium caseinate/high acyl gellan gum complexes: Stabilizing oil-in-water emulsions

In this work, the effects of pH and high acyl gellan gum concentration on the adsorption kinetics and interfacial dilatational rheology of sodium caseinate/high acyl gellan gum (CN/HG) complexes were investigated using a pendant drop tensiometer. In addition, stability related properties including interfacial protein concentration, droplet charge, size, microstructure and creaming index of emulsions were studied at different HG concentration (0–0.2 wt%) and pH values (4, 5.5 and 7). The results showed that HG adsorbed onto the CN mainly through electrostatic interactions which could lead to increase the interfacial pressure (π), rates of protein diffusion (kdiff), and molecular penetration (kp). The CN/HG complexes formed thick adsorption layers around the oil droplets which significantly increased the surface dilatational modulus with the increasing HG concentration. The CN/HG complexes appeared to form more elastic interfacial films after a long-term adsorption time compared with CN alone, which could reduce the droplet coalescence and thus prevented the growth of emulsion droplets. All four phosphorylated proteins of CN (αs1-, αs2-, β-, and κ-casein) were adsorbed at the oil-water (O/W) interface as confirmed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), and surface protein coverage increased progressively with increasing HG concentration at pH 5.5, but decreased at pH 7. The CN/HG stabilized emulsions at pH 5.5 revealed the higher net charges and smaller z-average diameters than those at pH 4 and pH 7. This study provides valuable information on the use of CN/HG complexes to improve the stability and texture of food emulsions.

A novel foam system stabilized by hydroxylated multiwalled carbon nanotubes for enhanced oil recovery: Preparation, characterization and evaluation

Carbon nanotube (CNT) is one of promising materials for stabilizing foam. However, the aggregation of CNT seriously affects its foam-stabilizing performance. Herein, this study employed the ultrasonic waves to improve the dispersity of hydroxylated multiwalled carbon nanotube (HMCNT) in SDBS solution. The ultrasonic treatment can disentangle the HMCNT through cavitation and chip effects and the SDBS molecules adsorbed on the HMCNT may increase the electrostatic repulsion between nanotubes, leading to a good dispersion of HMCNT. Besides the conventional evaluations in bulk phase, this study developed a visualized cylinder filled with quartz glass beads to estimate the foam properties in porous media. Experimental results indicate that the novel SDBS/HMCNT foam has a good foaming and foam-stabilizing performance both in bulk solution and porous media. A series of analysis experiments have been conducted to reveal the foam-stabilizing mechnism of HMCNT, including the surface tension and dilational viscoelastic modulus measurements, and the optical microscope and fluorescence microscope observations. This study found that the SDBS-modified HMCNT can adsorb on the gas-liquid interface and gather around the bubbles. As a result, the dilational viscoelasticity and thickness of foam films increase, which help to slow down the gas diffusion rate and restrain the film drainage. Finally, the fractured-core flooding tests showed that the SDBS/HMCNT foam system can effectively plug the millimeter-sized cracks in low-permeability cores and have a good potential in enhanced oil recovery.