Acid Droplets Research Articles

Mitigation Strategies against Antibody Aggregation Induced by Oleic Acid in Liquid Formulations.

Polysorbates 20 and 80 (PS20 and PS80) are commonly used in the formulations of biologics to protect against interfacial stresses. However, these surfactants can degrade over time, releasing free fatty acids, which assemble into solid particles or liquid droplets. Here, we apply a droplet microfluidic platform to analyze the interactions between antibodies and oleic acid, the primary free fatty acid resulting from the hydrolysis of PS80. We show that antibodies adsorb within seconds to the polar oleic acid-water interface, forming a viscoelastic protein layer that leads to particle formation upon mechanical rupture. By testing two different monoclonal antibodies of pharmaceutical origin, we show that the propensity to form a rigid viscoelastic layer is protein-specific. We further demonstrate that intact PS80 is effective in preventing antibody adsorption at the oleic acid-water interface only at low antibody concentrations and low pH, where oleic acid is fully protonated. Importantly, introduction of the amino acid l-arginine prevents the formation of the interfacial layer and protein particles even at high antibody concentrations (180 mg mL-1). Overall, our findings indicate that oleic acid droplets in antibody formulations can lead to the formation of protein particles via an interface-mediated mechanism. Depending on the conditions, intact PS80 alone might not be sufficient to protect against antibody aggregation. Additional mitigation strategies include the optimization of protein physicochemical properties, pH, and the addition of arginine.

Gas-liquid interfacial reaction mechanisms of typical small α-dicarbonyls in the neutral and acidic droplets: Implications for secondary organic aerosol formation

Small α-dicarbonyls (SαDs) are well-known as the important precursors of secondary organic aerosol (SOA). Hence, it is imperative to understand the atmospheric chemistry of SαDs to contribute to SOA formation. In this work, we investigated the interfacial chemistry of typical SαDs, including methylglyoxal (MG) and biacetyl (BA) in the neutral and acidic droplets by combined molecular dynamics and quantum chemical calculations. The trans configurations of MG and BA are found to be the favorable configurations at the interfaces and are prone to stay at the gas-liquid interface of the acidic droplet. The C=O group exhibits a preferential uptake orientation towards the interface because the carbonyl-O atom has a strong interaction with interfacial H2O. The uptakes and accumulations of MG and BA at the interfaces are promoted by the acidic condition. Subsequent interfacial hydrations of MG and BA in the acidic droplet are beneficial to yield diols, which can engage in oligomerization in the droplet interior to contribute SOA formation. Our results provide the theoretical insight into the interfacial chemistry of SαDs and their role in SOA formation.

Rapid aqueous-phase dark reaction of phenols with nitrosonium ions: Novel mechanism for atmospheric nitrosation and nitration at low pH.

Dark aqueous-phase reactions involving the nitrosation and nitration of aromatic organic compounds play a significant role in the production of light-absorbing organic carbon in the atmosphere. This process constitutes a crucial aspect of tropospheric chemistry and has attracted growing research interest, particularly in understanding the mechanisms governing nighttime reactions between phenols and nitrogen oxides. In this study, we present new findings concerning the rapid dark reactions between phenols containing electron-donating groups and inorganic nitrite in acidic aqueous solutions with pH levels <3.5. This reaction generates a substantial amount of nitroso- and nitro-substituted phenolic compounds, known for their light-absorbing properties and toxicity. In experiments utilizing various substituted phenols, we demonstrate that their reaction rates with nitrite depend on the electron cloud density of the benzene ring, indicative of an electrophilic substitution reaction mechanism. Control experiments and theoretical calculations indicate that the nitrosonium ion (NO+) is the reactive nitrogen species responsible for undergoing electrophilic reactions with phenolate anions, leading to the formation of nitroso-substituted phenolic compounds. These compounds then undergo partial oxidation to form nitro-substituted phenols through reactions with nitrous acid (HONO) or other oxidants like oxygen. Our findings unveil a novel mechanism for swift atmospheric nitrosation and nitration reactions that occur within acidic cloud droplets or aerosol water, providing valuable insights into the rapid nocturnal formation of nitrogen-containing organic compounds with significant implications for climate dynamics and human health.

HCl-induced emulsion and sludge formation affected by asphaltene type

Asphaltene may cause severe challenges during acid stimulation of oil wells. In the course of contact between crude oil and the injected acid (i.e. HCl), dispersed asphaltene molecules in the organic medium chemically adsorb and accumulate onto the surface of acid droplets due to interaction with acid ions. This causes forming a shear-resistance interfacial layer, known as acid-induced sludge, that prevents droplet coalescence and stabilizes the unwanted acid in oil emulsion. In this study, a set of compatibility tests was conducted to discern the emulsion stabilizing affinity of various asphaltene samples and sludge formation as a function of experimental variables including acid-to-mixture volumetric ratio (AMR) and pH, ferric ion, and asphaltene concentrations, aromaticity of the model oil, and shear (mixing speed). The utilization of heptol model oils (a mixture of heptane, toluene, and asphaltene) would help to focus on asphaltene behavior while isolating the other crude oil components. Five asphaltene samples (A1 to A5) having different structures were used in this study. Regardless of asphaltene properties, the emulsion stability was decreased approximately 70 % by increasing AMR. In addition, more aromaticity of the model oil resulted in 80 % less emulsion stability. There is a minimum range for emulsion stability in the interval of 500–1000 ppm asphaltene concentration for all samples. Up to 50 % emulsion stability was detected in the case of asphaltene A3 because of basic properties and higher colloidal instability. The effect of ferric ion concentration on intensifying emulsion stability and sludge formation was noticeable up to 500 ppm. HCl-model oil emulsion and the formed sludge had no sensitivity to shear force in the range of 500–1500 rpm due to the very low viscosity of the model oil. Therefore, in the studied shear range, emulsion and sludge formation have been more chemically controlled instead of being physically limited due to mixing. Moreover, sludge formation is not affected by pH of the HCl solution higher than 2 and mixing speed.

Hepatic and metabolic outcomes induced by sub-chronic exposure to polystyrene microplastics in mice.

Microplastics (MPs) have attracted significant attention due to their global distribution in living environments. Although some studies have reported MP-induced hepatotoxicity in mouse models, a systematic approach to MP-mediated liver toxicity was still lacking. Therefore, we used a mouse model to study the sub-chronic effects of MP exposure on the liver. Female C57BL/6 mice, aged 6weeks, received an oral administration of 0.3mg of Nile Red-labeled polystyrene (PS) microplastics, with particle sizes of 0.5µm (submicron) and 5µm (micron), via gavage, while control mice received vehicle only. Each mouse was exposed to MPs twice a week for 12weeks. After sacrifice, the levels of MP accumulation, oxidative stress, inflammation, and pathological changes were measured in the mouse liver, and blood samples were collected for serum biochemistry analysis. Our results demonstrated that 0.5µm PS-MPs were accumulated in mouse livers post-MP exposure, but not in the 5µm MP exposure group. Simultaneously, increased levels of glucose, triglyceride, alanine transaminase (ALT), aspartate transaminase (AST), superoxide dismutase, 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA), interleukin-6, and lipid droplets were found in the 0.5µm MP exposure group, while the fewer responses, including elevated liver weight index, glucose, high-density lipoprotein, AST, and decreased HNE-MA were observed in 5µm MP exposure group. These results indicate that sub-chronic exposure to submicron MPs causes MP deposition in mouse livers, which further induces oxidative stress, increases inflammatory cytokines and perturbs glucose and lipid homeostasis, which might trigger more severe metabolic dysfunction or non-alcoholic steatohepatitis-like hepatotoxicity.

Photochemistry of Imidazole-2-carbaldehyde in Droplets as a Potential Source of H2O2 and Its Oxidation of SO2.

Hydrogen peroxide (H2O2) plays a crucial role as an oxidizing agent within the tropospheric environment, making a substantial contribution to sulfate formation in hydrated aerosols and cloud and fog droplets. Field observations show that high levels of H2O2 are often observed in heavy haze events and polluted air. However, the source of H2O2 remains unclear. Here, using the droplets formed in situ by the deliquescence of hygroscopic compounds under a high relative humidity (RH), the formation of H2O2 by the photochemistry of imidazole-2-carbaldehyde (2-IC) under ultraviolet irradiation was explored. The results indicate that 2-IC produces IM-C•-OH and IM-C•═O radicals via H transfer itself to its excited triplet state and generates H2O2 and organic peroxides in the presence of O2, which has an evident oxidizing effect on SO2, suggesting the potential involvement of this pathway in the formation of atmospheric sulfate. H2O2 formation is limited in acidic droplets or droplets containing ammonium ions, and no H2O2 is detected in droplets containing nitrate, whereas droplets containing citric acid have an obvious promotion effect on H2O2 formation. These findings provide valuable insights into the behaviors of atmospheric photosensitizers, the source of H2O2, and the formation of sulfate in atmospheric droplets.

Fabrication of RC filters from a single printed Zn layer by reactive inkjet printing

This paper presents the development of planar zinc (Zn) resistor–capacitor (RC) filters from a single printed layer that are both printed and treated at room temperature. The fabrication process involves screen printing the resistor, capacitor and interconnects in a single patterned layer on kraft paper substrates using a Zn microparticle ink. In order to form a distinct resistor and capacitor in the patterned structure, reactive inkjet printing (RIJ) was performed to selectively dispense acetic acid on the RC filter pattern to achieve regions with highly contrasting resistance. The required high degree of spatial contrast was achieved using the positional control of the inkjet printer combined with the number of print passes and drop spacing used to dispense the acetic acid droplets. X-ray diffraction and scanning electron microscopy showed the crystal structure and grain size of Zn microparticles remained unchanged with increasing acetic acid exposure while the prominence of cold-welding increased with increasing exposure. Zn-based RC filters sharing a common set of dimensions but with a wide range of corner frequencies were successfully fabricated using this process. For a fixed filter geometry, the corner frequencies could be tuned from ∼7 kHz to ∼1 MHz as the number of print passes used to form the resistor increased in a stepwise manner. To the best of our knowledge, this is the first room temperature printing process to produce side-by-side resistors and conductors from the same printed layer and the first printing process of any type to produce RC filters with such a wide range of corner frequencies.

Photocatalytic chloride-to-chlorine conversion by ionic iron in aqueous aerosols: a combined experimental, quantum chemical, and chemical equilibrium model study

Abstract. Prior aerosol chamber experiments show that the ligand-to-metal charge transfer absorption in iron(III) chlorides can lead to the production of chlorine (Cl2/Cl). Based on this mechanism, the photocatalytic oxidation of chloride (Cl−) in mineral dust–sea spray aerosols was recently shown to be the largest source of chlorine over the North Atlantic. However, there has not been a detailed analysis of the mechanism that includes the aqueous formation equilibria and the absorption spectra of the iron chlorides nor has there been an analysis of which iron chloride is the main chromophore. Here we present the results of experiments measuring the photolysis of FeCl3 ⋅ 6H2O in specific wavelength bands, an analysis of the absorption spectra of FeCln3-n (n=1 … 4) made using density functional theory, and the results of an aqueous-phase model that predicts the abundance of the iron chlorides with changes in pH and iron concentrations. Transition state analysis is used to determine the energy thresholds of the dissociations of the species. Based on a speciation model with conditions extending from dilute water droplets and acidic seawater droplets to brine and salty crust, as well as the absorption rates and dissociation thresholds, we find that FeCl2+ is the most important species for chlorine production for a wide range of conditions. The mechanism was found to be active in the range of 400 to 530 nm, with a maximum around 440 nm. We conclude that iron chlorides will form in atmospheric aerosols from the combination of iron(III) cations with chloride and that they will be activated by sunlight, generating chlorine (Cl2/Cl) from chloride (Cl−) in a process that is catalytic in both chlorine and iron.

Molecular Dynamics Simulations of Native Protein Charging via Proton Transfer during Electrospray Ionization with Grotthuss Diffuse H3O.

Unraveling the mechanism by which native proteins are charged through electrospray ionization (ESI) has been the focus of considerable research because observable charge states can be correlated to biophysical characteristics, such as protein folding and, thus, solution conformation. Difficulties in characterizing electrosprayed droplets have catalyzed the use of molecular dynamics (MD) to provide insights into the mechanisms by which proteins are charged and transferred to the gas phase. However, prior MD studies have utilized metal ions, primarily Na+, as charge carriers, even though proteins are primarily detected as protonated ions in the mass spectra. Here, we propose a modified MD protocol for simulating discrete Grotthuss diffuse H3O+ that is capable of dynamically altering amino-acid protonation states to model electrospray charging and gaseous ion formation of model proteins, ubiquitin, and myoglobin. Application of the protocol to the evaporation of acidic droplets enables a molecular perspective of H3O+ coordination and proton transfer to/from proteins, which is unfeasible with the metal charge carriers used in previous MD studies of ESI. Our protocol recreates experimentally observed charge-state distributions and supports the charge residue model (CRM) as the dominant mechanism of native protein ionization during ESI. Additionally, our results suggest that protonation is highly specific to individual residues and is correlated to the formation of localized hydrated regions on the protein surface as droplets desolvate. Considering the use of discrete H3O+ instead of Na+, the developed protocol is a necessary step toward developing a more comprehensive model of protein ionization during ESI.

Stretchable photochromic hydrous TiO2‐embedded glycerol‐poly(dimethylsiloxane) film for rewritable information storage

AbstractPhotoreversible, color‐changing films have great potential in various optical applications. In this study, we developed a photochromic film by embedding droplets of metatitanic acid (hydrous TiO2) and glycerol in commercially available poly(dimethylsiloxane) (PDMS) silicone elastomers. Benefiting from the electron–hole pair scavenging abilities of glycerol, the resulting film exhibited rapid photoresponse, high photoreversible stability, excellent antiaging capability, and remarkable stretchability. The degree of color changes upon ultraviolet (UV) irradiation was effectively controlled by adjusting both the concentration of hydrous TiO2 (1–20 wt%) and UV irradiation time (5–30 min), thereby increasing total color‐changing ability (ΔE). High‐resolution patterns could be repetitively printed, erased, and rewritten (≥20 times) with no significant loss of clarity. After a 30‐day exposure to ambient air, there were no significant aging effects in the photochromic ability of the films, thus demonstrating promising potential as rewritable films for information storage.

Electrical effects on droplet behaviour

The effect of charge on water droplets modulates various aspects of their behaviour. These include the droplet stability, evaporation, and lifetime. Microphysical models have been developed such that a reasonably good understanding of these processes has been achieved. However, the specific effects of charge deserve further scrutiny as they are an intrinsic component of the factors controlling droplet characteristics. Describing the effects of these requires an understanding of the electrostatic pressure present in the droplet and its surface tension. One way to test these effects and assess droplet response to charge is to take an experimental approach to make observations directly. In this study, individual droplets are levitated in an acoustic wave to allow isolated measurements to be taken. The droplets are monitored using a CCD camera with a microscope objective lens. In some cases, with sufficient charge present, effects on droplet stability can be observed as Rayleigh explosions, where a sudden drop in mass is seen superimposed on the evaporation profile. These events also allow the charge on the droplet to be calculated, which is then compared with the droplet evaporation. Another factor that plays a part in droplet behaviour is droplet composition. Different substances have different surface tension, and this is explored by performing some experiments on sulphuric acid droplets. Theory predicts that the more highly charged a droplet is, the more resistant to evaporation it becomes. Experimental data collected during this study agrees with this, with more highly charged droplets observed to have slower evaporation rates. However, highly charged drops were also observed to periodically become unstable during evaporation and undergo Rayleigh explosions. Each instability of a highly charged drop removes mass, reducing the overall droplet lifetime regardless of the slower evaporation rate. The sulphuric acid droplets were observed to be much more resistant to evaporation and no Rayleigh instabilities were observed.

Rosin-inspired robust superhydrophobic coating for ensuring stable super-slippery properties

Superhydrophobic coatings infused with lubricants to form super-slippery surfaces have tremendous potential for applications in various fields. However, the robustness of superhydrophobic coatings remains a major challenge limiting their application and promotion. Herein, we developed a synergistically reinforced superhydrophobic coating (SRSC) using naturally-derived rosin as an adhesive to graft hydrophobic nanoparticles. The SRSC surface, with hierarchical micro−/nanostructure, exhibited remarkable mechanical and chemical robustness, enduring sandpaper abrasion, tape-peel, water/sand impact, and exposure to acid, alkali, and salt solutions without significant damage. When infused with perfluoropolyether lubricating oil to obtain the SRSC-based super-slippery surface, it could easily repel low-surface-energy and corrosive droplets (e.g., hot water, sump oil, alkali, and acid droplets). Importantly, such super-slippery surface exhibits remarkable resistance to icing. Furthermore, the surface demonstrates self-healing capabilities and controlled movement of oil droplets along specific wetting pathways resembling the shapes of “8” and “COS” under external energy stimulation. These findings are expected to promote the development and application of superhydrophobic coatings in real-world scenarios.

Synthesis and characterization of ZnO-SiO2 hybrid nanoparticles as an effective inhibitor for marine biofilm and biofouling

In the current study, we have created a highly efficient, economical, and environmentally friendly antifouling approach. ZnO nanoparticles were isolated from Avicennia Marina (a mangrove forest) and combined with SiO2 nanoparticles. ZnO-SiO2 hybrid nanoparticles were synthesized under reflux circumstances (with a 3:1 ratio, 45 mL of ethanol, 4 droplets of sulfuric acid, and 120 °C). ZnO-SiO2 hybrid nanoparticles were characterized through various techniques. Results showed the formation of Si-ZnO bond, indicated by a decrease in the strength of the peak at 470 cm−1 in the FTIR spectra. XRD analysis confirmed the presence of a crystal structure with a crystallite size of 30.72 nm. FE-SEM and TEM revealed spherical and hexagonal morphologies with sizes ranging from 17 to 49 nm and 8.94 nm, respectively. EDS analysis confirmed the presence of Zn, Si, and O elements in the nanoparticles. The minimum inhibitory concentration (MIC) of ZnO-SiO2 hybrid nanoparticles was assessed in the presence of Escherichia coli (50 μg/mL) and Staphylococcus aureus (25 μg/mL), and 10 mg/ml of the ZnO-SiO2 hybrid nanoparticles were capable of inhibiting 88 % of the Isochrysis galbana algae after 48 h, demonstrating their strong potential as an effective inhibitor. In addition, the ZnO-SiO2 hybrid nanoparticles were immersed in natural seawater at varying concentrations for a duration of 90 days to evaluate their effectiveness. The panel containing 3 wt% ZnO-SiO2 hybrid nanoparticles exhibited the most prosperous and efficient outcomes and had the least amount of biofouling (68.3 g). The findings of this research indicate that hybrid nanoparticles of ZnO-SiO2 possess promising and favorable characteristics for antifouling purposes.

Theoretical characterization of the kinetics of the multiphase ozonolysis of an aqueous maleic acid droplet

Theoretical characterization of the kinetics of the multiphase ozonolysis of an aqueous maleic acid droplet

Smart Surfaces with pH-Responsiveness Enhanced by Multiscale Hierarchical Structures Fabricated by Laser Direct Writing.

In contemporary applications, smart surfaces capable of altering their properties in response to external stimuli have garnered significant attention. Nonetheless, the efficient creation of smart surfaces exhibiting robust and rapid responsiveness and meticulous controllability on a large scale remains a challenge. This paper introduces an innovative approach to fabricate smart surfaces with strong pH-responsiveness, combining femtosecond laser direct writing (LDW) processing technology with stimulus-responsive polymer grafting. The proposed model involves the grafting of poly(2-diethylaminoethyl methacrylate) (PDEAEMA) onto rough and patterned Au/polystyrene (PS) bilayer surfaces through Au-SH bonding. The incorporation of LDW processing technology extends the choice of microstructures and roughness achievable on material surfaces, while PDEAEMA imparts pH responsiveness. Our findings revealed that the difference in contact angle between acidic and basic droplets on the rough PDEAEMA-g-Au surface (∼118°) greatly surpasses that on the flat PDEAEMA-g-Au surface (∼72°). Next, by leveraging the precision control over surface microstructures enabled by the LDW processing technique, this difference was further augmented to ∼127° on the optimized patterned PDEAEMA-g-Au surface. Further, we created two distinct combined smart surfaces with varying wettability profiles on which the hydrophilic-hydrophobic boundaries exhibit reliable asymmetric wettability for acidic and basic droplets. Additionally, we prepared a separator, realizing a better visual distinction between acid and base and collecting them separately. Given the effective abilities found in this study, we postulate that our smart surfaces hold substantial potential across diverse applications, encompassing microfluidic devices, intelligent sensors, and biomedicine.

Thyroid hormone increases fatty acid use in fetal ovine cardiac myocytes.

Cardiac metabolic substrate preference shifts at parturition from carbohydrates to fatty acids. We hypothesized that thyroid hormone (T3 ) and palmitic acid (PA) stimulate fetal cardiomyocyte oxidative metabolism capacity. T3 was infused into fetal sheep to a target of 1.5 nM. Dispersed cardiomyocytes were assessed for lipid uptake and droplet formation with BODIPY-labeled fatty acids. Myocardial expression levels were assessed PCR. Cardiomyocytes from naïve fetuses were exposed to T3 and PA, and oxygen consumption was measured with the Seahorse Bioanalyzer. Cardiomyocytes (130-day gestational age) exposed to elevated T3 in utero accumulated 42% more long-chain fatty acid droplets than did cells from vehicle-infused fetuses. In utero T3 increased myocardial mRNA levels of CD36, CPT1A, CPT1B, LCAD, VLCAD, HADH, IDH, PDK4, and caspase 9. Invitro exposure to T3 increased maximal oxygen consumption rate in cultured cardiomyocytes in the absence of fatty acids, and when PA was provided as an acute (30 min) supply of cellular energy. Longer-term exposure (24 and 48 h) to PA abrogated increased oxygen consumption rates stimulated by elevated levels of T3 in cultured cardiomyocytes. T3 contributes to metabolic maturation of fetal cardiomyocytes. Prolonged exposure of fetal cardiomyocytes to PA, however, may impair oxidative capacity.

Esterification of Oleic Acid for Biodiesel Production Using a Semibatch Atomization Apparatus

Although biodiesel production is undoubtedly a mature technology, there are still ways to improve it, especially through process intensification. The present study investigated the esterification of oleic acid with ethanol for biodiesel production in a nonconventional atomization reactor. The effects of the oleic acid flow rate (1.3, 2.6, and 3.9 g/min), atomization pressure (50, 100, and 150 kPa), and temperature (323, 333, and 343 K) were evaluated by a complete factorial experimental design. The size of droplets was determined by computational image processing. A mathematical model was also developed to describe the conversion of oleic acid to ethyl ester as a function of molar concentration of components and operating conditions of the reactor. A hybrid estimation of parameters (pre-exponential factor, activation energy, and equilibrium and solubility constants) was performed using particle swarm optimization followed by the Broyden–Fletcher–Goldfarb–Shanno method. The Pareto analysis has shown that the increase in temperature in the reactor and the increase in atomization pressure have improved the conversion of oleic acid. Higher pressure values in the atomization nozzle led to the generation of small oleic acid droplets, which accelerated reagent consumption during the reaction. On the other hand, conversion values were reduced by increasing the oleic acid flow rate. The highest conversion of oleic acid (86.7%) was obtained under the following reaction conditions: temperature of 343 K, atomization pressure of 150 kPa, oleic acid flow rate equal to 1.3 g/min using 0.7% sulfuric acid (mol of sulfuric acid/mol of oleic acid), and 2 h of reaction time. The simulations showed that esterification is governed by temperature, but it is possible to observe that the atomization pressure affects more conversion of oleic acid under a low temperature (&lt;323 K).

Optical manipulation and fusion of aqueous droplets containing inorganic and organic solutes in air using the dual-beam laser trapping technique.

The comparative evaluation of two aerosol droplets of different chemical compositions using the dual-beam laser trapping technique can be employed for highly sensitive and accurate measurements of the water activities of such droplets. However, it is technically difficult to load droplets of different chemical compositions into adjacent optical traps that are only a few tens of micrometers apart. To overcome this challenge, a chamber with an overhanging roof was created. This roof prevented the initially trapped droplets from being contaminated by aerosol droplets that were subsequently introduced into the chamber. Herein, we report the simultaneous laser trapping of an aqueous ammonium sulfate (AS) droplet and an aqueous succinic acid (SA) droplet in air using the dual-beam laser trapping technique. Two droplets were successfully fused through optical manipulation to form a mixed inorganic/organic droplet in air. This experimental approach is advantageous because it forms mixed inorganic/organic droplets under constant relative humidity (RH) conditions. However, in previous studies, it was necessary to compensate for changes in RH prior to and after droplet fusion. To assess the validity of theoretical predictions of the water activity of droplets containing AS and SA, the equilibrium radii of the droplet were compared with those calculated using certain theoretical models.

Experimental investigation of the acid-oil emulsion stability influenced by operational conditions and oil properties

Improper design of acidizing may cause new induced formation damages in the form of stable acid-oil emulsion, which would hinder fluid flow inside the pore passages of reservoirs. Furthermore, unwanted reduction of injected acid capability to resolve precipitations and rock should also be expected because the acid droplets are trapped in crude oils. There are not enough experimental studies and data on the effect of operating conditions and crude oil properties on the stability of acid-oil emulsions. This study focused on the formation of emulsion and its stability as well as acid-induced sludge formation for various crudes affected by mixing intensity (as a representation of acid injection rate to the reservoir), acid volume percent or AMR (as a representation of acid volume in the porous medium), temperature and crude oil viscosity. The experimental results showed that there exists a direct relation between emulsion stability and the mixing speed, which depends on crude oil properties such as viscosity and asphaltic compounds. Three crude samples of A, B and C from an oil reservoir were tested. Samples A and B showed 20 and 4 % higher emulsion stability at a mixing speed of 1500 rpm compared to that at 500 rpm. Higher shear rates produce larger interfacial areas and maybe easier and faster adsorption of various protonated asphaltenes and precipitates. Furthermore, changes in temperature from 30 to 85 °C caused 37 and 63 % increase in emulsion stability, probably because of higher droplets and molecules kinetic energy. AMR had a reverse impact in such a way that changing from 0.2 to 0.8 resulted in 87 % reduction in emulsion stability for both samples of A and B. However, the emulsion stability of sample C had not been changed by AMR, temperature and mixing shear rate. It seems that little sensitivity existed in the case of less viscous sample (C). It can therefore be inferred that crude oil properties are imperative during emulsion formation. More experiments were performed for diluted crude B by a mixture of toluene and heptane, keeping colloidal instability index intact, for reducing its viscosity from 56 to 2.5 cP at ambient temperature. Finally, a reduction of 17 % was observed in emulsion stability at 85 °C, AMR of 0.5 and mixing speed of 1500 rpm. The findings of this study facilitated a better understanding of operating conditions which influence the stability of HCl-oil emulsions during acidizing jobs.

On the Chemistry of Aqueous Ammonium Acetate Droplets during Native Electrospray Ionization Mass Spectrometry.

Ammonium acetate (NH4Ac) is a widely used solvent additive in native electrospray ionization (ESI) mass spectrometry. NH4Ac can undergo proton transfer to form ammonia and acetic acid (NH4+ + Ac- → NH3 + HAc). The volatility of these products ensures that electrosprayed ions are free of undesired adducts. NH4Ac dissolution in water yields pH 7, providing "physiological" conditions. However, NH4Ac is not a buffer at pH 7 because NH4+ and Ac- are not a conjugate acid/base pair (Konermann, L. J. Am. Soc. Mass Spectrom. 2017, 28, 1827-1835.). In native ESI, it is desirable that analytes experience physiological conditions not only in bulk solution but also while they reside in ESI droplets. Little is known about the internal milieu of NH4Ac-containing ESI droplets. The current work explored the acid/base chemistry of such droplets, starting from a pH 7 analyte solution. We used a two-pronged approach involving evaporation experiments on bulk solutions under ESI-mimicking conditions, as well as molecular dynamics simulations using a newly developed algorithm that allows for proton transfer. Our results reveal that during droplet formation at the tip of the Taylor cone, electrolytically generated protons get neutralized by Ac-, making NH4+ the net charge carriers in the weakly acidic nascent droplets. During the subsequent evaporation, the droplets lose water as well as NH3 and HAc that were generated by proton transfer. NH3 departs more quickly because of its greater volatility, causing the accumulation of HAc. Together with residual Ac-, these HAc molecules form an acetate buffer that stabilizes the average droplet pH at 5.4 ± 0.1, as governed by the Henderson-Hasselbalch equation. The remarkable success of native ESI investigations in the literature implies that this pH drop by ∼1.6 units relative to the initially neutral analyte solution can be tolerated by most biomolecular analytes on the short time scale of the ESI process.