Multilayer Formation Research Articles

Unraveling the Applicability of LbL Coatings for Drug Delivery in Dental Implant-Related Infection Treatment.

Peri-implantitis is an inflammatory condition caused by bacterial biofilms adhered on dental implant surfaces that cause progressive tissue destruction from the host's inflammatory response. The adverse effects of peri-implantitis progression can go beyond just losing the implant. This highlights the importance of implementing strategies to stabilize disease in the short term. Layer-by-layer (LbL) assembly is a promising avenue in the field of peri-implantitis management due to its applicability with a variety of substances, in addition to being an easy, versatile, and flexible process for multilayer formation to act directly in the affected site. In this Review, our objective is to offer comprehensive chemical and biological insights into the LbL system, clarifying its specific application as antimicrobial coatings, with concern for the physical site and purpose. Additionally, we delve deeper into the concepts of onset and progression of peri-implantitis, aiming to elucidate the precise indications for employing the LbL system as a coating for implant abutments in peri-implantitis treatment. Finally, we correlate the chemical composition of the LbL system with its functionality while also addressing the challenges posed by the uncontrolled environment of the oral cavity, which ultimately restricts its clinical applicability.

Mixed Adsorption Mono- and Multilayers of ß-Lactoglobulin Fibrils and Sodium Polystyrene Sulfonate

The formation of beta-lactoglobulin (BLG)/sodium polystyrene sulfonate (PSS) complexes decelerates the change in the surface properties of the mixed solutions with the surface age and increases the steady-state dilational surface elasticity in a narrow PSS concentration range. At the same time, the changes in the surface properties are accelerated in the dispersions of BLG fibrils with and without PSS due to the influence of small peptides coexisting with fibrils. A decrease in the peptide concentration as a result of the dispersion purification leads to slower changes in the surface properties at low PSS concentrations. The increase in the polyelectrolyte concentration results in an increase in the steady-state surface elasticity due to the fibril/PSS complex formation and in very slow changes in the surface properties if the polyelectrolyte exceeds a certain critical value. The latter effect is a consequence of the formation of large aggregates and of an increase in the electrostatic adsorption barrier. The consecutive adsorption of BLG fibrils and PSS leads to the formation of regular multilayers at the liquid–gas interface. The multilayer properties change noticeably with an increase in the number of layers from four to six in agreement with previous results on the multilayers of PSS with an oppositely charged synthetic polyelectrolyte, presumably due to the heterogeneity of the first PSS layer. The dynamic elasticity of the multilayers approaches 250 mN/m, indicating that they can effectively stabilize foams and emulsions.

Facile Doping and Functionalization of Molybdic Acid into Nanobiochar to Enhance Mercury Ion Removal from Water Systems.

Functionalized nanomaterials with surface-active groups have garnered significant research interest due to their wide-ranging applications, particularly in water treatment for removing various contaminants. This study focuses on developing a novel, multi-functional nanobiosorbent by synthesizing nanosized biochar from artichoke leaves (NBAL) and molybdic acid (MA). The resulting nanobiosorbent, MA@NBAL, is produced through a microwave-irradiation process, offering a promising material for enhanced environmental remediation. The characteristics of assembled MA@NBAL were evaluated from SEM-EDX, XPS, TGA, FT-IR, and zeta potential detection. The size of particles ranged from 18.7 to 23.7 nm. At the same time, the EDX analysis denoted the existence of several major elements with related percentage values of carbon (52.9%), oxygen (27.6%), molybdenum (8.8%), and nitrogen (4.5%) in the assembled MA@NBAL nanobiosorbent. The effectiveness of MA@NBAL in removing Hg(II) ions was monitored via the batch study method. The optimized maximum removal capacity of Hg(II) ions onto MA@NBAL was established at pH 6.0, 30.0 min equilibrium time, and 20 mg of nanobiosorbent, providing 1444.25 mg/g with a 10.0 mmol/L concentration of Hg(II). Kinetic studies revealed that the adsorption process followed a pseudo-second-order model, with R2 values ranging from 0.993 to 0.999 for the two tested Hg(II) concentrations, indicating excellent alignment with the experimental data. This suggests that the chemisorption mechanism involves cation exchange and complex formation. Isotherm model evaluation further confirmed the adsorption mechanism, with the Freundlich model providing the best fit, yielding an R2 of 0.962. This result indicates that Hg(II) adsorption onto the surface of MA@NBAL nanobiosorbent occurs on a heterogeneous surface with multilayer formation characteristics. The results of the temperature factor and computation of the thermodynamic parameters referred to endothermic behavior via a nonspontaneous process. Finally, the valid applicability of MA@NBAL nanobiosorbent in the adsorptive recovery of 2.0 and 5.0 µg/mL Hg(II) from contaminated real aquatic matrices was explored in this study, providing 91.2-98.6% removal efficiency.

Adsorption isotherms and removal of lead (II) and cadmium (II) from aqueous media using nanobiochar and rice husk

Removal of Cd(II) and Pb(II) from aqueous solutions is a challenging task and the search for novel adsorbents is underway. This study examined the efficiency of nanobiochar (NB) and rice husk (RH) in the adsorption and removal of Cd(II) and Pb(II) from water. The effect of various physicochemical parameters such as initial pH, initial Cd and Pb concentration, adsorbent dosage, and contact time were tested. SEM/EDX images confirmed the adsorption of Pb and Cd with surface physical and chemical changes. The maximum Pb removal was noted at pH 6 using NB (96%) and at pH 8 for RH (90%), and the maximum Cd removal by NB was recorded at 8 pH (91%) and by RH at pH 6 (87%). The decline in adsorption intensity at lower pH suggested protonation of the adsorbent surface causing cation-cation repulsion. Most of the adsorption occurred within the initial 60 min. A continuous gradual increase in the adsorption with time suggested multilayer formation. Of the three isotherms, the Freundlich model fits the present data best, implying an infinite surface coverage and indicating the potential for multilayer adsorption of Pb and Cd on the surfaces of RH and NB adsorbents. In conclusion, this study highlights the promising potential of NB as a cost-effective adsorbent for the removal of Cd and Pb ions from aqueous solutions.

Removal of phosphate from wastewater using zirconium/iron embedded chitosan/alginate hydrogel beads: An experimental and computational perspective

Adsorptive removal of phosphate plays a crucial role in mitigating eutrophication. Herein, the Zr/Fe embedded chitosan/alginate hydrogel bead (Zr/Fe/CS/Alg) is reported as an effective phosphate adsorbent. This polymer nanocomposite is synthesized by the in-situ reduction of the metals on the polymer matrix. The synthesized adsorbent was characterized by the FTIR, SEM-EDX, TGA, BET, and XPS. The adsorbent showed a maximum phosphate adsorption capacity of 221.72 mg/g at pH 3. The experimental data fit well with the Freundlich isotherm and pseudo-second-order kinetics model, indicating a heterogeneous multilayer surface formation and a chemisorption-dominated adsorption process. Density Functional Theory (DFT) and Monte Carlo (MC) calculations revealed high negative adsorption energy due to the chemisorption of phosphate on the adsorbent. Hence, the major interactions such as electrostatic attraction, hydrogen bonding, and inner-sphere complexation of phosphate adsorption and Zr/Fe/CS/Alg hydrogel beads were investigated from the experimental and computational analysis. The negative values of thermodynamic parameters indicated a spontaneous, exothermic, and less random adsorption process. The synthesized adsorbent exhibited excellent selectivity toward phosphate and maintained 73 % efficiency after six adsorption/desorption cycles. The Zr/Fe/CS/Alg hydrogel beads reduced the phosphate concentration in real wastewater samples from 19.02 mg/L to 0.985 mg/L, suggesting that these nanocomposite hydrogel beads could be a promising adsorbent for real-world applications.

Fracture propagation behavior via multi-cluster fracturing in sandstone-shale interbedded reservoirs

Initiation and propagation of fractures in multi-layered formations has been a topic of interest for the efficient utilization of hydrocarbon resources. Although there is a reasonable body of knowledge to facilitate the design and development of hydraulic fracture, the understanding of initiation and propagation of fracture clusters in layered formation is limited. This paper discusses the findings from controlled laboratory experiments and numerical modeling to understand the initiation and propagation of hydraulic fracturing operations. True triaxial tests were carried out on samples extracted from outcrop representative of Lianggaoshan formation in China. It was noted that the differential stress between the layers is critical for the initiation and propagation of multiple fracture. It was also noted that the viscosity of the fracturing fluid influences the propagation of fractures across lamina and interfaces. The intermediatory response of rocks due to the injected fluid was studied through numerical modeling of the physical process using modified cohesive zone model, which was then validated by the output from the laboratory experiments. It was noted that the increase in the fracture cluster has the potential to constrain the extent of fracture propagation whereas decrease in the cluster size increases the extent of fracture propagation. Compared to sandstone, the fracture height in shale is 30% lower. For sandstone, early-stage fracture flow distribution stabilizes more quickly, and higher fluid pressure within fractures significantly increases fracture height and effective stimulation volume.

Optimizing junction interface integrity between 3D/2D defect pyrochlore Bi1.8Fe0.2WO6 and g-C3N4 nanostructures: A novel multifunctional nanocomposite for enhanced photocatalytic and photo-electrocatalytic water splitting and water remediation applications

In this work, a simplistic composite fabrication of defect pyrochlore Bi1.8Fe0.2WO6 (BFWO) and g-C3N4 (g-CN) was carried out to augment the photocatalytic degradation kinetics and Hydrogen (H2) evolution rate. The structural confirmation through XRD and FTIR confirmed the successful formation of pristine g-C3N4, BFWO NPs, and their composites. FESEM micrographs revealed multilayered sheet-like formation for C3N4 whereas irregular cuboid-shaped structure for BFWO NPs. In the composite formation, the sheets tended to appear wrapped around the BFWO NPs. The UV-DRS absorbance spectra exhibited a highlighted increase in the absorbance region towards the visible light region following a decrease in the band gap. The photoluminescence lifetime studies revealed an enhanced lifetime of excitons to 6.21 ns for 50:50 (g-C3N4: BFWO) composite formation, whereas pristine g-CN displayed an average lifetime of about 4.79 ns. The degradation efficacy in the removal of RhB and MB from water revealed up to 100% and 95.5% removal rates in under 90 mins and 180 mins respectively using the 50:50 composite formation. Similarly, the H2 evolution rate was significantly improved and exhibited up to 370 μmol/h/g. The photo-electrochemical studies revealed a sharp charge separation of excitons for 50:50 (g-C3N4: BFWO) with a maximum photocurrent density of -0.54 μA/cm2 @ 0 V which is 3.6 times and 13.5 times higher than bare g-CN and BFWO. 1.33 V vs. RHE for OER kinetics and -0.09 V vs RHE for HER kinetics were the minimal onset potential exhibited for equal ratios of BFWO and g-CN. Coupled with the heightened charge separation, reduced recombination rate, and optimal band edge positions, the photocatalytic efficiency in the degradation of RhB and MB and water-splitting reactions were improved.

Polycyclic aromatic hydrocarbon derivatives onto polar microplastics of polyurethane: equilibrium, thermodynamics, and kinetics of monolayer-multilayer adsorption.

The study of the adsorption of polycyclic aromatic hydrocarbons on microplastics (MPs) has attracted much attention as to how microplastics can act as carriers of these pollutants. Polyurethane (PU) is one of the MPs found in aquatic environments, containing different functional groups it can interact with polar and nonpolar molecules. PAH derivatives (dPAHs) present different properties and thus can be adsorbed by different interactions; thus, this study investigated the adsorption of fluorene (FLN), dibenzothiophene (DBT), dibenzofuran (DBF), and carbazole (CBZ) onto PU MP. The Langmuir, Freundlich, and BET isotherm models were examined, and the BET model best fitted. The adsorption was a nonspontaneous process, exothermic for mono- and multilayer formation for FLN, DBT, and CBZ, and endothermic for DBF monolayer formation. The adsorption monolayer was formed by van der Waals forces, H─bonding, and π─π interactions, while the formation of the multilayer can be explained by π─π and hydrophobic interactions. The pseudo-second-order model proved to be more consistent for the adsorption of dPAHs. The adsorption in artificial seawater shows no significant differences for the monolayer but favored the adsorption multilayer due to the salting-out effect. Due to the existence of several adsorption mechanisms, PU MP interacts with dPAHs in greater quantities when compared to a MP with a simpler structure.

Multi-layer formation by oxidation and solid-state crystallization of cold sprayed amorphous coatings during dry sliding wear

Amorphous alloy coatings, known for the exceptional wear resistance, have emerged as a key solution for enhancing the wear performance of magnesium alloys under harsh environments. In this study, Fe-based amorphous alloy coatings were deposited on magnesium alloy by cold spraying technology, and the influence of microstructural evolution on the wear performance of coatings under dry sliding wear conditions was discussed. The results showed that a dense adherent oxide layer with a thickness of ∼700 nm comprising nanograins of less than 8 nm was formed at the outmost surface, which played a role of self-lubricating. Underneath, a 1 μm thick nanocrystalline-amorphous layer with nanograins of ∼20 nm dispersed in the amorphous alloy matrix was formed through in-situ crystallization induced by flash temperature. This composite structure prevented the formation of shear bands in amorphous alloys and enhanced the durability. Therefore, the transition from abrasive wear to adhesive wear was a consequence of the microstructural evolution from a dual-phase composite layer to a self-lubricating oxide layer.

Enhanced compressive strength of graphene strengthened copper (G/Cu) composites

This study explores the compressive mechanical properties of copper composites reinforced with graphene. Graphene was synthesized on copper powders via plasma-enhanced chemical vapor deposition. Multilayer graphene formation has been substantiated by Raman analysis. Graphene-coated copper (G/Cu) powders were then subjected to pressing and sintering to fabricate G/Cu composites. The mechanical properties of G/Cu composites were investigated under compression from room temperature up to 400 °C in air. The results demonstrated a substantial improvement in the mechanical properties of G/Cu composites compared to monolithic copper. Specifically, the yield strength in compression of the G/Cu composite increased by 203% at room temperature and by 190% at 200 °C. At 400 °C, the yield strength enhancement exceeded 370%. Microstructural analysis suggests that the observed enhancements in G/Cu composites can be attributed to reduced porosity, smaller grain size, and inhibited dislocation motion at the increased grain boundary area (due to refined grain size) and graphene-copper interfaces.

Morphology-Dependent Interaction between Tetraphenylporphyrins and a Metal Oxide Surface: Electronic Signature, Photo Physics, and Chemical Interaction

Porphyrin-substrate hybrid systems are the building blocks in a series of materials, such as organic light-emitting diodes, chemical sensors, dye-sensitized solar cells and catalysts. Functional layers and 2D nanostructures on surfaces enable sensors, and nanoscale optical and magnetic materials. 3D porphyrin structures are for instance used in controlling and manipulating light at subwavelength dimensions. Understanding and correctly describing the way molecules interact with the substrate and in thin-film structures gives a handle on geometrical and electronic device properties. Indeed, adsorption and film-formation have a relevant effect on the molecular electronic structure even in the absence of strong covalent bonding, namely in terms of level-alignment with substrate states in the former and polarization-induced renormalization of molecular band gaps in the latter.Using the case of Co(II)-tetraphenylporphyrin (CoTPP) on the MgO(100), we shine light on the adsorption at morphology-related low-coordinated surfaces sites and the effect of multilayer film formation from a theoretical perspective in a frame work of hybrid density functional theory and many-body perturbation theory. We simulate the photoemission spectra for relevant adsorption sites as a fingerprint with distinct site-related features in both valence and core-level regions of the electronic structure that are also observed in experiments on MgO(100) films on Ag(100) and thus aid the identification of sites. Effects of the formation of porphyrin films on the electronic and optical properties will be outlined for H2TPP and MgTPP.We also highlight the self-metalation of H2TPP at morphology-related low-coordinated sites. Metalation is an important pathway for functionalization of porphyrin-based organic-inorganic structures. We address the self-metalation mechanism using ab initio molecular dynamics simulation at room temperature. While H2TPP is mobile on the pristine surface as the steric hindrance by phenyl rings prevents the physisorption of the macrocycle at a specific site, step edges or kink sites provide anchor points exposing low-coordinated, reactive oxygen-sites to hydrogens of the macrocycle. We report a spontaneous proton transfer at these sites forming an intermediate complex before the metalation occurs. This highlights the role of low-coordinated surface sites for the chemical interaction with the porphyrin.

Sustainable removal of methylene blue dye from textile effluents by magnetized Tea waste and Peanut shells

Methylene blue finds numerous applications across various industries but its prolonged exposure to living organisms can result in significant health risks. In this study, the adsorption of magnetized Peanut shells and Tea waste for methylene blue dye removal has been reported. The biosorbents were synthesized by co-precipitation method and their suitability for methylene blue adsorption was confirmed through characterization techniques including Scanning Electron Microscope, Fourier Transfer Infrared Spectroscopy and X-Ray Diffraction analysis. After optimizing for pH (8.0), temperature (312 k), biosorbents dosage 25 mg/L with contact periods (35 min for Tea waste@Fe3O4 and 40 min for Peanut shells@Fe3O4), and initial methylene blue concentrations (5 ppm), the removal percentages of 95.88 % for Tea waste@Fe3O4 and 84.11 % for Peanut shells@Fe3O4 were achieved effectively. The equilibrium data for MB dye adsorption fitted well with the Langmuir model (R2 = 0.99) for Tea waste@Fe3O4 which indicated the formation of monolayer formation of adsorbate at the surface of adsorbent and the Freundlich model (R2 = 0.98) for Peanut shells@Fe3O4 confirmed the multilayers formation of MB dye at the material surface. Kinetic studies specified that both Tea waste@Fe3O4 (R2 = 0.99) and Peanut shells@Fe3O4 (R2 = 0.99) followed the pseudo-second order. Thermodynamic analysis showed that the adsorption process on Tea waste@Fe3O4 and Peanut shells@Fe3O4 was spontaneous (−ΔG) and endothermic. Tea waste@Fe3O4 exhibited ΔH (27.97 kJ/mol) and entropy ΔS (93.69 kJ/mol) while ΔH = 208.9 kJ/mol and ΔS 62 kJ/mol were found for Peanut shells@Fe3O4. The performance of the proposed biosorbent in industrial effluent demonstrated their effectiveness, highlighting their potential as a cost effective and sustainable solution for wastewater treatment.

Porous media flow of polymeric nanofluids in multilayered formations: a simulation study

ABSTRACT The injection of viscoelastic fluids into the oil-bearing formations to push the bypassed and entrapped oil toward the producers is a widely accepted technique known for creating a stable displacement front and piston-like displacement, leading to Enhanced Oil Recovery (EOR). However, the sweep efficiency of such complex fluids in stratified formations is still a topic of debate in the literature and is problematic, particularly in harsh reservoir conditions. This research concerns how the inclusion of nanoparticles into the polymer solution could affect the porous media flow of polymeric fluids in multilayered reservoirs. Accordingly, validated core-scale numerical models for polymer flood and polymer nanohybrid flood were upscaled to develop a reservoir-scale model. Through numerical simulations using a compositional reservoir simulator, the simultaneous flow of crude oil and polymer nanohybrids in both low and high-permeable layers of the reservoir were scrutinized. The numerical outputs showed that, compared with polymer flood, the flow dynamics of the polymer nanohybrids in different layers of the reservoir are more favorable, which resulted in improved oil recovery of over 20% of Residual Oil In Place (ROIP). Additionally, our numerical findings indicated that the polymer nanohybrids could exhibit lower polymer adsorption and acceptable salt tolerance in porous media.

Xylooligosaccharides as emerging prebiotics and their sustainable generation from xylan catalysed by endoxylanase immobilized ordered mesoporous silica

The enzyme endo-1,4-β-xylanase has been a prominent candidate for research in recent years due to its ability to catalyse prebiotic production in an environmentally friendly manner. However, the loss of stability and activity when employed in industrial processes has prompted enzyme immobilization. The present study aims to compare the efficiencies of amorphous (such as fumed silica and silicic acid) and ordered mesoporous silica materials (including SBA-15, IITM-41, and MCM-41) as carriers for endoxylanase immobilization, particularly focussing on the novel silicate IITM-41. Recombinant endoxylanase from Bacillus subtilis KCX006 purified by Ni-NTA columns has been used in this study. XRD, TEM, and BET analyses of these nanostructured materials confirmed the mesoporous structure and the nature of the pores. FT-IR spectroscopy confirmed protein binding through characteristic functional group signatures of silica materials and proteins. Zeta potential values of the nanostructure materials became more negative after enzyme binding, and the confirmation of enzyme immobilization was achieved through fluorescent tagging. Although amorphous silica showed a higher yield of immobilization, it resulted in lower recovered activity due to the formation of protein multilayers. Among the ordered mesoporous silica materials, IITM-41 exhibited the highest recovered activity at 74 %, with a maximum yield of xylooligosaccharides reaching 797.61 mg/g. The optimum pH of the immobilized enzymes remained unchanged, but there was a shift in the optimum temperature from 50 to 60 °C, along with a broader optimal range, attributed to increased enzyme rigidity and substrate diffusion limitations. Kinetic parameters Km and Vmax were higher for immobilized enzymes compared to the free enzyme, particularly with higher Vmax values observed for enzymes immobilized on mesoporous materials compared to those on amorphous silica. Generally, mesoporous materials showed superior performance in terms of xylooligosaccharides production, storage stability, and recycling efficiency. Over 10 cycles of reuse, mesoporous materials exhibited a higher yield of total xylooligosaccharides (ranging from X2 to X6) compared to amorphous silica.

Adsorption of acetonitrile on Pt(1 1 1) surface: Combining insights from experiment and theory

The extensive use of acetonitrile in various fields of organic synthesis and electrochemistry has provided widespread interest in studying the processes of acetonitrile adsorption on metal surfaces. In this work, the adsorption of acetonitrile and deuterated acetonitrile on thePt(111)surface was studied by polarization–modulation infrared reflection-absorption spectroscopy in the temperature range of 80–150 K. It was found that the adsorption and desorption of acetonitrile on platinum occurred in the molecular form. The possible configuration of adsorption with coordination through the nitrogen atom was proposed. To support the interpretation of obtained experimental data, density functional theory calculations were performed for acetonitrile adsorption considering 2 types of possible adsorption configurations: “bridge” with both N and C atoms bonded to the surface (η2(C,N) mode) and “top” with coordination through the nitrogen atom (N-top mode). Adsorption energies and frequency shifts of acetonitrile were calculated for different coverages ofPt(111)surface, including the second molecular layer. A joint experimental-theoretical study confirmed the formation of ice-like multilayers of acetonitrile onPt(111)under the considered conditions when C≡N bond is kept.

Nanoscale surface defects of goethite governing DNA adsorption process and formation of the Goethite-DNA conjugates

In urbanized areas, extracellular DNA (exDNA) is suspected of carrying genes with undesirable traits like virulence genes (VGs) or antibiotic resistance genes (ARGs), which can spread through horizontal gene transfer (HGT). Hence, it is crucial to develop novel approaches for the mitigation of exDNA in the environment. Our research explores the role of goethite, a common iron mineral with high adsorption capabilities, in exDNA adsorption processes. We compare well-crystalline, semi-crystalline, and nano goethites with varying particle sizes to achieve various specific surface areas (SSAs) (18.7–161.6 m2/g) and porosities. We conducted batch adsorption experiments using DNA molecules of varying chain lengths (DNA sizes: <11 Kb, <6 Kb, and <3 Kb) and assessed the impact of Ca2+ and biomacromolecules on the adsorption efficacy and mechanisms. Results show that porosity and pore structure significantly influence DNA adsorption capacity. Goethite with well-developed meso- and macroporosity demonstrated enhanced DNA adsorption. The accumulation of DNA on the goethite interface led to substantial aggregation in the system, thus the formation of DNA-goethite conjugates, indicating the bridging between mineral particles. DNA chain length, the presence of Ca2+, and the biomacromolecule matrix also affected the adsorption capacity and mechanism. Interactions between DNA and positively charged biomacromolecules or Ca2+ led to DNA compaction, allowing greater DNA accumulation in pores. However, a high concentration of biomacromolecules led to the saturation of the goethite surface, inhibiting DNA adsorption. AFM imaging of goethite particles after adsorption suggested the formation of the DNA multilayer. The study advances understanding of the environmental behavior of exDNA and its interaction with iron oxyhydroxides, offering insights into developing more effective methods for ARGs removal in wastewater treatment plants. By manipulating the textural properties of goethite, it's possible to enhance exDNA removal, potentially reducing the spread of biocontamination in urban and industrial environments.

Numerical Simulation of Hydraulic Fracture Propagation on Multilayered Formation Using Limited Entry Fracturing Technique

Hydraulic fracturing is one of the most effective stimulation methods for unconsolidated sandstone reservoirs. However, the design of hydraulic fracturing must take into account the mechanical and stress properties of different geological formations between layers. In this paper, a three-dimensional coupled fluid-solid model using the finite element method is developed to investigate multiple vertical fractures at different depths along a vertical wellbore under different geological and geomechanical conditions. The finite element model does not require further refinement of any new cracks, requiring much smaller degrees of freedom and higher computational efficiency. In addition, new elements were used to account for local pressure drop due to perforation entry friction along the vertical wellbore. Numerical simulation results indicate that hydraulic fracture connections are observed from adjacent layers. Furthermore, the low stress contrast and high Young’s modulus between the layers increases the likelihood of multiple fracture connections. Higher fluid leakage rates increase the likelihood of fracture branching, but decrease the area of fracture coverage near the wellbore. Increasing fluid viscosity is effective in improving the area of fracture coverage near the wellbore. These findings are useful for the design of hydraulic fracturing in multi-layered formations in unconsolidated sandstone formations.

Discontinuous Shear Thickening of Suspensions of Magnetic Particles in Relation to the Polymer Coating on Their Surfaces

The phenomenon of discontinuous shear thickening (DST) is observed in suspensions of solid particles with a very high-volume fraction. It is characterized by an abrupt decrease in the shear rate for critical stress during a ramp of stress. This behavior can be reproduced in numerical simulations by introducing a local friction between two particles above a given local force. We present experimental results showing this DST behavior obtained with suspensions of magnetic (iron) and nonmagnetic (calcium carbonate) particles and different amounts of a superplasticizer molecule used in the cement industry. For both types of particles, the same behavior was observed with first an increase in critical stress with the amount of plasticizer followed by a decrease at higher concentrations but with a larger viscosity before critical stress was reached. At a low concentration of plasticizer, the low critical stress is interpreted by the local sliding of plasticizer molecules on the surface of particles. At higher concentrations, when total coverage is achieved, the critical stress is higher since it has to remove the molecules out of the surface. At still higher concentrations, the increase in viscosity is explained by the formation of multilayers of molecules on the surface of the particles. This interpretation is supported by the measurement of the adsorption isotherm of the plasticizer on the surface of the particles.

Research on the factors influencing the width of hydraulic fractures through layers

The method of segmented hydraulic fracturing in the coal seam roof has proven to be an efficient technique for coalbed methane exploitation. However, the behavior of hydraulic fractures in multilayer formations with significant differences in mechanical properties is still unclear. This paper studied the variation in hydraulic fracture width at the coal-rock interface by employing experimental method with a true triaxial hydraulic fracturing experimental system and numerical simulation method. Results revealed that the hydraulic fracture more likely to expanded along the coal-rock interface instead of break through it with the small horizontal stress difference and low flow rate injection condition. And improving the injection flow rate lager than a critical value, the hydraulic fracture tends to break through the coal-rock interface. Hydraulic fractures in both mudstone and coal beds exhibited a trend of increasing and then decreasing of fracture width at the interface. Since the strength of the coal seam was lower compared to that of the mudstone, maintaining high pressure was no longer necessary when the hydraulic fracture crossed the interface and entered the coal seam, leading to a reduction in fracture width within the mudstone. During the later stages of fracturing, the entry of proppant into the coal seam became challenging, resulting in a phenomenon characterized by excessive fluid but insufficient sand. The time required for the fracture width to traverse the proppant was found to be inversely proportional to the difference in horizontal ground stress and the flow rate of the fracturing fluid. And it was directly proportional to the modulus of elasticity, permeability of the coal seam, and interface strength. The interface strength has the greatest influence on the width of hydraulic fractures. In conclusion, this study provides valuable insights into the behavior of hydraulic fractures in multilayer formations with varying mechanical properties. The findings contribute to a better understanding of the factors affecting hydraulic fracture width within coal seams, which can ultimately enhance the efficiency of coalbed methane exploitation.

Asphaltene Adsorption on Solid Surfaces Investigated Using Quartz Crystal Microbalance with Dissipation under Flow Conditions.

Asphaltenes can cause operational challenges in petroleum production facilities and adversely affect production by adsorption on mineral surfaces and alteration of the oil wettability of reservoirs. Therefore, understanding asphaltene adsorption mechanisms and their effects is crucial to improving the efficiency of oil production and reducing costs. In this study, we focus on understanding the impact of asphaltene concentration and the depositing environment of asphaltene adsorption on solid surfaces using the quartz crystal microbalance with dissipation (QCM-D) technique. The initial and long-term kinetics of adsorption at different concentrations were examined on three different solid surfaces including silicon dioxide to represent quartz mineral, stainless steel, and gold. The frequency-dissipation data showed evidence of monolayer adsorption initially, followed by multilayer formation. At short times, the adsorbed mass increased linearly with time, suggesting that the process was kinetically controlled rather than diffusion-controlled. The results were reproducible and did not depend on convection velocity but did depend on the surface material. At later stages, the monolayer development appeared to follow the random sequential adsorption (RSA) theory. Once multilayer adsorption commenced, the rates agreed well with the two-layer model of Zhu and Gu, 1990. The impact of asphaltene adsorption on the wettability of the surface was examined using contact angle studies, which showed decreasing water wettability with an increase in the adsorbed mass. The contact angle of water after 12 h of adsorption leveled off at around 100° on all three surfaces. Contact angle measurements were also used to evaluate if brine salinity causes the wettability alteration of surfaces with the adsorbed asphaltene. The results indicate that at 3% NaCl solution, the contact angle decreased only slightly by less than 2°.