Neutral Wetting Research Articles

Preparation and Interfacial Behavior of Mg-based Nanosheets

Abstract Two-dimensional nanosheets have attracted considerable attention as oil displacement agent due to their unique interfacial properties. But the high cost limits the application of traditional nanosheets. In this study, a hydrophilic magnesium-based nanosheet (HMN) was synthesized and modified to obtain the amphiphilic magnesium-based nanosheets(AMN). The influences of reaction time, reaction temperature, stirring rate and raw materials ratio of product were studied and the optical reaction condition were summed up as follows: reaction time was 27 h, reaction temperature was 50 °C, stirring rate was 100 rpm, magnesium source: synthetic agent was 0.5:1. Though AFM, SEM and TEM, it was confirmed that nanosheets were two-dimensional sheet-like with 100-300 nm of plane size and 4-20 nm of thickness size. FTIR confirmed the successful modification of AMN from HMN. AMN had good interfacial properties, 0.05wt% AMN could reduce the oil-water interfacial tension from 34.67 mN/m to 1.08 mN/m, and make the oil wet glass into a neutral wetting. Furthermore, emulsion could be formed by AMN with an ultralow concentration (10 mg/L), while a stable interfacial film could be formed at higher concentrations(500mg/L). The low cost and simple synthesis of AMN make it a unique oil displacement agent with great interfacial properties and promise when compared to traditional nanosheets.

High-pressure homogenization to improve the stability of liquid diabetes formula food for special medical purposes: Structural characteristics of casein–polysaccharide complexes

The stability of diabetes formula food for special medical purposes (D-FSMP) was improved by high-pressure homogenization (HPH) at different homogenization pressures (up to 70 MPa) and number of passes (up to 6 times). The process at 60 MPa/4 times was the best. Casein had the highest surface hydrophobicity in this condition. The casein–polysaccharide complexes were endowed with the smallest size (transmission electron microscopy images). The complex particles exhibited nearly neutral wettability (the three-phase contact angle was 90.89°), lower interfacial tension, and the highest emulsifying activity index (EAI) and emulsifying stability index (ESI). The prepared D-FSMP system exhibited the narrowest particle size distribution range, the strongest interfacial deformation resistance and the best storage stability. Therefore, an appropriate intensity of HPH could enhance the stability of D-FSMP by improving the interfacial and emulsifying properties of casein–polysaccharide complexes. This study provides practical guidance on the productions of stable D-FSMP.

A molecular dynamics study on pore structure: Performance comparison between metal foam and artificial mesh porous surface

With the development of surface engineering, porous surfaces have emerged as a significant research subject in boiling heat transfer. The latter, in turn, plays a crucial role in various industries such as power plants, distillation plants, and microelectronic technology. In this paper, the Molecular Dynamics method is adopted to investigate the wicking dynamics and boiling dynamics of two porous surfaces: foam, which exhibits randomly distributed pores, and mesh, composed of ordered square wires with relatively uniform pore sizes. Three wettability, namely hydrophilic, neutral, and hydrophobic wetting states, are assigned to the two porous surfaces de-coupling the effect of wettability from surface structure. Results reveal that, during the wicking process, the foam surface shows better wetting ability as it absorbs liquid under both hydrophilic and neutral wettability. Comparatively, the mesh surface has the fastest wicking speed under hydrophilic wettability yet it becomes non-wetting under neutral wettability. During the boiling process, the boiling dynamics differ greatly under three wettability. More importantly, the difference in surface structure makes the foam surface possess a better heat transfer whereas the mesh surface causes gentle pressure variation. Our findings provide insights into the design of artificial porous surfaces for certain purpose and their potential application.

Determination of the oil saturation coefficient according to Dakhnov–Archi using a new methodological approach when studying core samples

Background. Predisposition of the rock to wetting by water (hydrophilicity) or oil (hydrophobicity) has a significant influence on the results of determining the oil saturation coefficient according to Dakhnov–Archi. Carbonate reservoir rocks in most cases are characterized by a complex type of wettability: heterogeneous (selective), mixed or neutral wettability. Collectively, the surface properties of such rocks can be defined by the term “nonhydrophilic wettability”. Studying rocks with nonhydrophilic wettability using standard core research methods can lead to subsequent errors in calculating oil reserves using the volumetric method. Objective. To eliminate the risk of such errors by adapting standard research methods, in particular the centrifugation method, to the results of experiments in reservoir conditions. Materials and methods. Capillarimetric method (semipermeable membrane method), centrifugation method, core “aging”. Results. The results of core studies necessary for calculating the oil saturation coefficient of nonhydrophilic reservoirs using formation resistivity data using the Dakhnov–Archi method are presented. A methodological approach is proposed for adapting the centrifugation method to reservoir conditions. Conclusions. The applied methodological approach makes it possible to increase the volume of statistical data and calculate an adequate value of the oil saturation coefficient according to Dakhnov–Archi for nonhydrophilic reservoirs.

Correlating Electrolyte Infiltration with Accessible Surface Area in Macroporous Electrodes using Neutron Radiography

Carbon-based porous electrodes are commonly employed in electrochemical technologies as they provide a high surface area for reactions, an open structure for fluid transport, and enable compact reactor architectures. In electrochemical cells that sustain liquid electrolytes (e.g., redox flow batteries, CO2 electrolyzers, capacitive deionization), the nature of the interaction between the three phases - solid, liquid and gas - determines the accessible surface area for reactions, which fundamentally determines device performance. Thus, it is critical to understand the correlation between the electrolyte infiltration in the porous electrode and the resulting accessible surface area in realistic reactor architectures. To tackle this question, here we simultaneously perform neutron radiography with electrochemical measurements to correlate macroscopic electrode saturation/wetting with accessible surface area. We find that for untreated electrodes featuring neutral wettability with water, the electrode area remains underutilized even at elevated flow rates, both for interdigitated and parallel flow fields. Conversely, increasing the electrode hydrophilicity results in an order-of-magnitude increase in accessible surface area at comparable electrode saturation, and is less influenced by the electrolyte flow rate. Ultimately, we reveal useful correlations between reactor architectures and electrode utilization and provide a method that is broadly applicable to flow electrochemical reactors.

Engineering Interconnected Open-Porous Particles via Microfluidics Using Bijel Droplets as Structural Templates.

Designing porous structures is key in materials science, particularly for separation, catalysis, and cell culture systems. Bicontinuous interfacially jammed emulsion gels represent a unique class of soft matter formed by kinetically arresting the separation of the spinodal decomposition phase, which is stabilized by colloidal particles with neutral wetting. This study introduces a microfluidic technique to create highly interconnected open-porous particles using bijel droplets stabilized with hexadecyltrimethylammonium bromide (CTAB)-modified silica particles. Monodisperse droplets comprising a hydrophobic monomer, water, ethanol, silica particles, and CTAB were initially formed in the microfluidic device. The diffusion of ethanol from these droplets into the continuous cyclohexane phase triggered spinodal decomposition within the droplets. The phase-separated structure within the droplets was stabilized by the CTAB-modified silica particles, and subsequent photopolymerization yielded microparticles with highly interconnected, open pores. Moreover, the influence of the ratio of the CTAB and silica particles, fluid composition, and microchannel direction on the final structure of the microparticles was explored. Our findings indicated that the phase-separated structure of the particles transitioned from oil-in-water to water-in-oil as the CTAB/silica ratio was increased. At intermediate CTAB/silica ratios, microparticles with bicontinuous structures were formed. Regardless of the fluid composition, the pore size of the particles increased with time after phase separation. However, this coarsening was arrested 15 s after droplet formation in the CTAB-modified silica particles, accompanied by a change in the particle shape from spherical to ellipsoidal. In situ observations of the bijel droplet formation revealed that the particle shape deformation is caused by the rolling of elastic bijel droplets at the bottom of the microchannel. As such, the channel setup was altered from horizontal to vertical to prevent the deformation of bijel droplets, resulting in spherical particles with open pores.

Construction and characterization of pickering emulsion gels stabilized by β-glucans microgel particles

Amidst the rising demand for protein and starch, polysaccharide-based microgel particles (MPs) offer a sustainable solution as Pickering emulsion gel (PEG) stabilizer. β-glucans, known for their resistance to rapid digestion, enable targeted ingredient delivery and intestinal health modulation. A novel PEG stabilizer was developed by incorporating non-gelatinous polysaccharide 1,3-α/β-D-glucan into gelatinous polysaccharide 1,3-β-D-glucan after thermally induced gelation and microgelation. Following the blending of these polysaccharides, the three-phase contact angle of the resulting composite β-glucans MPs was modified from 126.6° to 94.7°, achieving nearly neutral wettability. Moreover, the particle size was reduced from 6.64 to 2.74 μm, accompanied by a potential of −21.55 mV. These structural modifications facilitated improved adsorption properties of MPs at the oil-water interface, subsequently leading to complete coverage of the oil droplet surface. Consequently, this process resulted in the formation of small, uniformly distributed emulsion droplets. Confocal laser microscopy revealed that the β-glucans MPs either interconnected to create gel networks or coated with oil droplets. This phenomenon established a thick barrier that prevented oil droplet aggregation and conferred semi-solid physical properties of the PEG. It is worth noting that particle concentration and oil content significantly influenced droplet size, rheological properties, and the stability of PEGs. Specifically, PEGs with prolonged stability were successfully constructed at low MP concentrations (0.6–1.0 wt%) and low oil content (20–50 wt%). This research introduces an innovative approach for structuring liquid oil, with potential applications in fat replacement.

The role of alginate in starch nanocrystals-stabilized Pickering emulsions: From physical stability and microstructure to rheology behavior

Sodium alginate (SA) was used as a co-stabilizer to improve the Pickering emulsions stabilized by starch nanocrystals (SNC). Compared with pure SNC, SNC/SA complexes possess better neutral wettability with the contact angle approaching to 90°, more surface negative charges, and lower oil–water interfacial tension. These properties of particles make as-prepared emulsion higher stability with the lower creaming index and average droplet size. Furthermore, the emulsion exhibited good stability against salt (0–600 mM) and pH (2.0–6.0) at higher SA concentration (1.0 wt%). Confocal laser scanning microscopy (CLSM) images proved that SNC could be effectively adsorbed at the oil–water interface with the aid of SA. Rheological analysis showed that higher content of SA resulted in improved strength and higher viscosity of emulsion system. Results from this work indicating that SA could be a useful co-stabilizer to fulfill the demands of Pickering emulsions stabilized by SNC with stable characteristics.

The pore-network modeling of gas-condensate flow: Elucidating the effect of pore morphology, wettability, interfacial tension, and flow rate

The gas-condensate flow in the near-well region is significantly influenced by phase behavior, flow regimes, and pore geometries. In conventional gas-condensate reservoirs the key pore-scale parameters affecting gas and condensate relative permeabilities include velocity (i.e., pressure gradient), interfacial tension (IFT), wettability, and pore structure. To examine the impact of these parameters, three-dimensional (3D) and two-dimensional (2D) pore-network models (PNMs) were developed. A proposed compositional model was used to implement the cyclic process of condensate corner flow (film flow for circular tubes) and condensate blockage. Response surface methodology (RSM) was employed to achieve high accuracy in phase equilibrium calculations and to enhance computational speed.The 3D PNM simulations of gas-condensate core-flood experiments confirmed the consistency and accuracy of the implemented methodology. A parametric study of governing factors such as pore shapes, wettability, IFT, and flow rate was conducted using the developed PNMs. The findings revealed that pore geometry and contact angle dictate the condensate meniscus curvature and snap-off process in pore throats. The unblocking of throats by condensate bridges was primarily controlled by contact angle, IFT, and pore cross-section. A shift to neutral wetting substantially improved gas-condensate flow in higher IFTs and angular pore shapes.The positive velocity effect on low-IFT gas-condensate flow, known as the coupling rate effect, was more pronounced in simulations with lower contact angles, and its impact was negligible at neutral wettability, similar to the IFT effect. The simulation results and findings underscore the influence of each factor and offer a method for incorporating the effects of pore shape (i.e., formation type and structure), contact angle, velocity, and IFT in continuum scale simulations.

Influence of Drop Viscosity and Surface Wettability on Impact Outcomes

To understand the effects of liquid viscosity and surface wettability on the outcomes for a drop impacting perpendicularly on a dry, clean surface at a normal temperature and pressure, experiments were conducted for a wide variety of droplets and substrate surfaces. These experiments included a range of receding contact angles (from ~18° to ~150°) and liquid viscosities (from 1 cp to 45 cp); the broadest such combination is yet published. The surface wettabilities were quantitatively characterized using a new set of definitions: superphillic (θrec < 30°), phillic (30° < θrec < 90°), phobic (90° < θrec < 150°), and superphobic (θrec > 150°). Six different outcome regimes were found (including a new beaded deposition outcome) as a function of Ohnesorge number, Weber number, and the cosine of the receding contact angle. The beaded deposition is a hybrid of the well-known splash and deposition outcomes. The critical Weber number that separates the outcome boundaries was found to be significantly influenced by both the Ohnesorge numbers and the receding contact angle. In particular, there is a consistent reduction in the critical Weber number from superphilic to philic to neutral wettability conditions. Interestingly, this same decreasing trend line continues from neutral to phobic to superphobic conditions, but instead, it separates the regimes of deposition and bouncing. At higher Weber numbers, an additional boundary regime was found between splashing and bounce, which also decreased as the surface wettability decreased. This same type of trend was seen for several Ohnesorge numbers, indicating that wetting characterization should be based on the contact angles for the combination of the droplet liquid and the surface. In addition, a new regime map for droplet rebound on superphobic surfaces was obtained from the present and previous results indicating (for the first time) that the total rebound generally occurs for Weber numbers between 2.2 and 32 with Ohnesorge numbers less than 0.17. Additional studies are recommended to explore an even broader range of test conditions (especially intermediate wettability conditions), the separate influence of advancing and/or hysteresis contact angles, and to include the effects of the inclination angle, gas pressure, and heat transfer.

Self-organization and dewetting kinetics in sub-10 nm diblock copolymer line/space lithography

In this work, we investigated the self-assembly of a lamellar block copolymer (BCP) under different wetting conditions. We explored the influence of the chemical composition of under-layers and top-coats on the thin film stability, self-assembly kinetics and BCP domain orientation. Three different chemistries were chosen for these surface affinity modifiers and their composition was tuned in order to provide either neutral wetting (i.e. an out-of-plane lamellar structure), or affine wetting conditions (i.e. an in-plane lamellar structure) with respect to a sub-10 nm PS-b-PDMSB lamellar system. Using such controlled wetting configurations, the competition between the dewetting of the BCP layer and the self-organization kinetics was explored. We also evaluated the spreading parameter of the BCP films with respect to the configurations of surface-energy modifiers and demonstrated that BCP layers are intrinsically unstable to dewetting in a neutral configuration. Finally, the dewetting mechanisms were evaluated with respect to the different wetting configurations and we clearly observed that the rigidity of the top-coat is a key factor to delay BCP film instability.

Formation and physical characterization of soy protein-isoflavone dispersions and emulsions

Proteins stabilize emulsions by adsorbing at the interface to prevent the natural tendency of droplet coalescence. Polyphenols (plant-derived secondary metabolites) are capable of complexing with proteins through structural interactions. Certain polyphenols have shown influence on interfacial properties of proteins, yet isoflavones specifically have not been widely investigated. Thus, the objective of this research was to study the effect of isoflavones on protein-stabilized oil-in-water emulsions. Soy protein fractions, assessed via SDS-PAGE and bicinchoninic acid assay, contained primarily β-conglycinin (7S) and glycinin (11S). Notable isoflavones identified from HPLC analysis were daidzin, genistin, and glycitin. Physical characteristics (size, zeta potential, polydispersity index, and wettability) of soy protein isolate-isoflavone (SPI–I) dispersions and emulsion droplets were measured with a Zetasizer Nano ZS and goniometer. Isoflavone addition significantly increased the contact angle of sessile drops towards neutral wettability. Heating appeared to significantly improve colloidal stability and emulsion droplets formed with heated SPI-I dispersions sustained size (∼200–245 nm) and zeta potential (∼-30-35 mV) over 7 days, with higher concentrations of isoflavones being generally correlated with smaller emulsion droplets. Collectively, these findings indicate that isoflavone addition improved emulsion stability compared to the control without isoflavones and that they can contribute to colloidal stability of food products.

Impact of nanoparticles–surfactant solutions on carbon dioxide and methane wettabilities of organic-rich shale and CO2/brine interfacial tension: Implication for carbon geosequestration

Rock wetting behaviour and CO2/brine interfacial tension (IFT) have significant impacts on enhanced hydrocarbon recovery (EOR) and carbon geo-sequestration (CGS) projects. Influence of nanoparticles/surfactant solutions (NPS) flooding on EOR and CGS in sandstone and carbonate formation have been examined in recent studies. But the impact of NPS on carbon dioxide (CO2) and methane (CH4) wettabilities of organic-rich shale and CO2/brine IFT is presently unclear. Thus, we measured contact angles, [advancing (θa) and receding (θr)] for CO2/brine and CH4/brine on Marcellus shale with high total organic carbon (14.8 wt%), as well as CO2/brine IFT with Krüss drop shape analyzer (DSA 100) through the sessile drop and pendant drop techniques. Prior to IFT and contact angles measurement, the shale samples were aged in NPS solutions to evaluate the impact of NPS treatment on CO2 geo-storage. Low-cost rice husk silica nanoparticles and saponin surfactant were used for the study due to their environmental friendliness and economic attractiveness. At geo-storage conditions (25 MPa and 353 K), the advancing contact angle of untreated shale was measured as θa=116.22° (CO2-wet condition), whereas the receding contact angle was measured as θr=82.88° (near neutral wettability). However, θa reduced by 56.34° whereas θr reduced by 56.76° when the shale substrate was treated with 0.1 wt% SiO 2 and 0. 2 wt% saponin solutions. CO2/NPS IFT were lower than CO2/brine IFT and the CH4 wettability of the Marcellus shale was significantly lower than the CO2 wettability at all investigated conditions. Contact angles decreased with temperature and increased with CO2/CH4 pressure, whereas CO2/NPS IFT exhibited an opposite trend. The reduction in contact angles and CO2/brine IFT by NPS have significant impacts on adsorption trapping of CO2 in organic-rich shale and hydrocarbon recovery from unconventional shale reservoirs.

Interfacial decoration of desalted duck egg white nanogels as stabilizer for Pickering emulsion

Pickering emulsions, stabilized by food-grade protein colloidal particles, have demonstrated potential in food, cosmetics, and medical applications, while their environmental instability remains serious challenges. Herein, in this study, we have prepared a simple but effective interfacial decoration method based on the noncovalent interaction between desalted duck egg white nanogels (DEWN) and natural polyphenol for enhancing the interfacial and environmental stability of Pickering emulsions. As demonstrated, the introduction of tannic acid (TA) tuned near neutral wettability (θo/w∼90°) of the DEWN-TA (named DEWN-Tn) colloidal particles and significantly lowered the interfacial tension. Subsequently, the emulsions with distinct TA concentrations were further investigated. The results presented a decrement in the droplet sizes by adding appropriate concentrations of TA and long-term storage stability. The rheological behavior explored that the addition of TA did increase in both G′ and G″ compared with a solely DEWN-based system. Furthermore, it was worth noting that the decoration of TA under optimized conditions could also increase heat and pH stability and effectively inhibit “salting-out” effects of the Pickering emulsions system. Our study implies a possibility of fabricating interfacial architecture on the oil-water interface, which possesses great potential to be used as excellent food-grade emulsifiers.

In Situ Produced Nanoparticles at the Oil-Water Interface for Conformance Control and Enhanced Oil Recovery.

Nanoparticle-assisted enhanced oil recovery (Nano-EOR) has attracted intensive interest in the laboratory as a promising oil recovery technology. However, the nanoparticles' stability and long-distance delivery of nanoparticles (NPs) in large-scale reservoirs are two main challenges. In this work, we developed a novel concept of in situ synthesizing NPs at the oil-water interface inside the reservoir for EOR instead of injecting presynthesized NPs from outside. The pore-scale flooding experiments show that EOR efficiencies for tertiary flooding were 6.3% without reaction (Case 3), 14.6% for slow reaction (Case 1), and 25.4% for relatively quick reaction (Case 4). Examination of the EOR mechanism shows that in situ produced SiO2 NPs in microchannels could alter the substrate wettability toward neutral wetting. Moreover, the produced NPs tended to assemble on the immiscible oil-water interface, forming a barrier toward interface deformation. As the reaction continued, excessive surface-modified NPs could also diffuse into aqueous brine and accumulate as a soft gel in the flowing path swept by brine. Collectively, these processes induced a "shut-off" effect and diverted displacing fluids to unswept areas, which consequently increased the sweep efficiency and improved the oil recovery efficiency. Auxiliary bulk-scale experiments also showed that the reaction-induced nanoparticle synthesis and assembly at an immiscible interface reduced the interfacial tension and generated an elastic oil-water interface.

Impact of weakly charged insoluble karaya gum on zein nanoparticle and mechanism for stabilizing Pickering emulsions

The effect of weakly charged insoluble karaya gum (KG) on zein colloidal nanoparticles (ZKGPs) for stabilizing Pickering emulsions was investigated. Due to weak surface charge, KG could cover the surface of zein particles by hydrogen bonds and weak electrostatic interactions. With the increase in coverage, the zeta potential of ZKGPs changed from positive to negative values close to zero and the average particle size tended to become larger. The closest neutral wettability (89.85°) was achieved when the zein/KG mass ratio was 1:1. The samples prepared with high oil volume fraction (φ = 0.5–0.75) and high particle concentration (1.0–1.3 %, w/v) formed emulsion gels easily and showed higher storage stability. CLSM images also confirmed that ZKGPs could be distributed in the continuous phase to enhance the emulsion network structure. Consequently, weakly charged ZKGPs reduced the emulsification energy barrier and increased the coverage and steric hindrance of particles at the oil/water interface. These findings provide new ideas for the development of stable Pickering emulsions for application in food textural modification as well as encapsulation and delivery of bioactive substances.

A novel Pickering emulsion stabilized solely by hydrophobic agar microgels

A novel agar-based Pickering emulsion stabilizer was developed through the hydrophobic modification and microgelation of agar. After hexanoylation, the three-phase contact angle of hexanoylated agar (HAG) particles was adjusted from approximately 60° to 96° closing to neutral wettability. After microgelation, the particle size of the modified agar microgel was approximately 2 μm and Zeta potential reached −23.63 mV. Confocal laser microscopy and cryogenic scanning electron microscopy showed that HAG microgels formed a gel network or embedded on the surface of oil droplets, thus providing a dense barrier for oil droplets to coalesce and Ostwald ripening. The oil volume fraction and particle concentration had a significant effect on the droplet size and rheological properties of the Pickering emulsion. Pickering emulsion gels with long-term storage stability was prepared at low particle concentrations (0.7 wt%) and lower oil fractions (φ = 0.3– 0.5), which might become a new effective delivery system for bioactive substances.

Gas-liquid competitive adsorption characteristics and coal wetting mechanism under different pre-adsorbed gas conditions

Coal seam water injection was widely used to prevent mine gas and dust disasters. It is undeniable that the gas adsorbed on coal surface can influence the coal-water wettability. In order to investigate how the gas environment affects the coal-water contact characteristics, the coal-water contact angle was tested under different gas environments, including CH4, N2 and He. Then the microscopic wetting mechanism were revealed by combing with the molecular dynamic simulation. Results showed that, the coal-water contact angle gradually increases in the range of 0 ∼ 2 MPa. The contact angle shows the most significant growth trend in CH4 environment, increasing from 72.11° to 106.9°, and the wettability transits from hydrophilic wetting (<90°) to neutral wetting (=90°), eventually it becomes hydrophobic wetting (>90°). At the same gas pressure, the coal-water contact angle in the CH4 atmosphere is the largest, followed by N2 atmosphere and He atmosphere. Molecular dynamics simulation results showed that the adsorption capacity of water molecules decreases as the pre-adsorption gas pressure grows. The adsorption capacity of water molecules decreased from 1.84 mmol/g, 2.04 mmol/g and 2.23 mmol/g to 1.46 mmol/g, 1.51 mmol/g and 1.69 mmol/g under CH4, N2 and He atmosphere, respectively. Furthermore, the surface free energy and adsorption energy of water and gas were analyzed, finding that the surface free energy drops down with the rising pressure and the gas adsorption capacity, leading to the poor wettability. The adsorptive gas shows a more remarkable effect in weakening coal-water wettability due to the gas adsorption layer and gas–water competitive adsorption.

Oscillations of a partially wetting bubble

We study the linear stability of a compressible sessile bubble in an ambient fluid that partially wets a planar solid support, where the gas is assumed to be an ideal gas that obeys the adiabatic law. The frequency spectrum is computed from an integrodifferential boundary value problem and depends upon the wetting conditions through the static contact angle$\alpha$, the dimensionless equilibrium bubble pressure$\varPi$, and the contact-line dynamics that we assume to be either (i) pinned or (ii) freely moving with fixed contact angle. Corresponding mode shapes are defined by the polar-azimuthal mode number pair$[k,\ell ]$with$k+\ell =\mathbb {Z}^{+}_{even}$. We report instabilities to the (i)$[0,0]$breathing mode associated with volume change, and (ii)$[1,1]$mode that is linked to horizontal centre-of-mass motion of the bubble. Stability diagrams and instability growth rates are computed, and the respective instability mechanisms are revealed through an energy analysis. The zonal$\ell =0$modes are associated with volume change, and we show that there is a complex dependence between the classical volume and shape change modes for wetting conditions that differ from neutral wetting$\alpha =90^\circ$. Finally, we show how the classical frequency degeneracy for the Rayleigh–Lamb modes of the free bubble splits for the azimuthal modes$\ell \neq 0,1$.

SiO2 synergistic modification of siloxane thickener to improve the viscosity of supercritical CO2 fracturing fluid

ABSTRACT Supercritical carbon dioxide (SC-CO2) fracturing technology has the advantages of CO2 storage and waterless fracturing and has great application potential in the development of unconventional oil and gas resources. However, the low viscosity of SC-CO2 limits the development of this technology. This paper investigates the synergistic effect of nanomaterials on a developed thickener (HBD-2, high branched D4H). The research results show that among the five micro/nanomaterials Cu-BTC, SiO2, MCC, MWCNTs, and TiO2, only SiO2 has a good synergistic effect on the HBD-2/SC-CO2 system, and significantly improves its thickening, temperature resistance, temperature resistance and shear resistance. At 60s−1, 305.15 K and 10 MPa, 5 wt.% HBD-2 + 1 wt.% SiO2 increased the apparent viscosity of SC-CO2 to 5.82 mPa·s(The viscosity of 5 wt.% HBD-2 under the same conditions is 4.48 mPa·s). The apparent viscosity of SC-CO2 is positively correlated with pressure and SiO2 dosage and negatively correlated with temperature and shear rate. The SiO2/HBD-2 system can effectively avoid clay swelling and can change the water wetness on the core surface to neutral wettability. In addition, we also studied the mechanism of SiO2 in HBD-2/SC-CO2 thickening system by RDF(radial distribution function). The results show that the introduction to SiO2 shifts the peak position of the system to the left and enhances the peak intensity. The macroscopic manifestation is the enhancement of the apparent viscosity of HBD-2/SC-CO2.This paper proves the feasibility of nanomaterials to synergize SC-CO2, and provides a new thread for the research and development of SC-CO2 thickeners in the future.