Liquid Drainage Research Articles

Enhancing CO2 Foam Stability with Hexane Vapours: Mitigating Coarsening and Drainage Rates

CO2 foams often suffer from poor stability due to high coarsening and coalescence rates, limiting their effectiveness in various applications. While it is well-established that small amounts of insoluble vapours such as alkane or fluorocarbon vapours can impede coarsening and recent studies have demonstrated their impact on coalescence, their specific effect on the CO2 foams has not been studied. This research provides a comprehensive examination of stabilising effect of hexane on CO2 foams in the presence of sodium dodecylbenzenesulfonate (SDBS). We investigated the foam stability of CO2 foams, benchmarking them against N2 foams by analysing foam lifetime, liquid drainage rate, and the evolution of bubble size. Additionally, we quantified the stabilising impact of hexane by calculating the coarsening rate. To gain insights into the adsorption mechanism of surfactants in the presence of hexane, we conducted surface tension and interfacial dilational rheology measurements, which demonstrated an increased adsorption of surfactant molecules at the interface and increased dilational viscoelasticity of interface when n-hexane was present. The introduction of hexane significantly improved foam stability, reducing coarsening rates by more than an order of magnitude. This improvement in foam stability is attributed to inhibited CO2 diffusion from the bubbles, as well as enhanced surfactant adsorption and surface elasticity, resulting in an approximate 3.6-fold increase in foam half-life.

Rapid water drainage on human eyelashes of a hydrophobic Brachistochrone fiber array.

Numerous organisms exploit asymmetrical capillary forces generated by unique fiber or asymmetrical tapered structures to rapidly eliminate undesired liquid for survival in moist or rainy habitats. Human eyelashes, the primary protector of eyes, use a yet-to-be-fully-understood mechanism to efficiently transfer incoming liquid for vision safeguarding. Here, we elucidate that human eyelashes featuring a hydrophobic curved flexible fiber array with surface micro-ratchet and macro-curvature approximating the Brachistochrone is adept at directionally and rapidly expelling incoming liquid to maintain clear vision. These structural attributes are sequentially used for liquid drainage, starting from anisotropic retention via micro-ratchet, followed by the elastic expulsion among deflected hydrophobic flexible fiber arrays and culminating in the fastest sliding off along a Brachistochrone path, which together reduce the contact time by about 20% of that on rigid linear slopes. Investigating the intricate relationship between multistructure and draining efficiency of human eyelashes may inspire the design of advanced liquid-repelling edges on outdoor devices to maintain dryness.

Air/water interfacial properties and thin film drainage dynamics of compositionally diverse wheat flour water extracts

The role of water-extractable (WE) wheat flour constituents and their interactions in determining the stability of wheat-based foam-type foods remain largely unexplored. Additionally, the contribution of drainage dynamics of the thin liquid films (TLFs) between gas bubbles to food foam stabilization is often overlooked. We here investigated the air/water (A/W) interfacial, TLF drainage, and foaming properties of compositionally diverse wheat flour aqueous extracts. Such extracts were prepared and then either used as such or modified by dialyzing out (i) low molecular mass constituents or (ii) both low molecular mass constituents and enzymatically hydrolyzed carbohydrates. This approach resulted in extracts with gradually increasing protein contents and distinct carbohydrate compositions. Wheat extract constituents created highly elastic A/W interfaces, regardless of the type of extract modification, suggesting a significant contribution from WE wheat proteins. TLFs stabilized by wheat extracts from which low molecular mass constituents were removed had significantly greater stability. This was ascribed to an increased disjoining pressure caused by steric repulsive forces, which in turn were attributed to the interaction between high molecular mass arabinoxylan in the bulk and adsorbed proteins at the A/W interfaces. All extracts showed similarly good foaming properties, implying a dominant role for WE wheat proteins in determining foaming. The strongly elastic A/W interfaces formed by WE wheat proteins likely reduced liquid drainage to such extent that coalescence and disproportionation were largely delayed. The findings of this study could facilitate further investigations on the possibility of tuning protein-AX interactions toward improved foam stability.

Overpotential Characteristic and Flow Field Structure for High Power Output of HT-PEFC

Polymer electrolyte fuel cells (PEFCs) are used for automobiles and other applications due to their excellent startup ability and load followability. From now on, PEFCs are expected to be widely applied to commercial applications. However, when conventional PEFC needs high-load operation, insufficient cooling capacity becomes a major issue. This is due to the small temperature difference between the FC stack and the outside air. The conventional electrolyte membrane uses the water as a proton-conducting path, so PEFC’s operation temperature must be controlled below 100°C. Therefore, applying high-temperature PEFC (HT-PEFC) is effective to improve cooling capacity. HT-PEFC can operate at high-temperature (above 100°C) by doping the acid as a proton conducting path in the polymer electrolyte membrane. In this study, we evaluated the effects of the temperature, the gas pressure, and the gas flow field structure on the power output at high-temperature.Figure 1 shows the structure and picture of HT-PEFC single cell used in this study. Polybenzimidazole (PBI) -based MEA APM STD25 (reaction area: 5 x 5 cm2) manufactured by Advent Technologies was used. The performance was compared by using the straight flow channels (pitch: 2.0 mm, 1.0 mm) and the porous flow field (porosity: 91%) for the separator. All experiments are conducted with non-humidified air and hydrogen.Figure 2 shows the I-V characteristics at various cell temperature and gas pressure with the 2.0 mm pitch straight flow channel. As the cell temperature increases, the I-V characteristic improves, especially in the low-medium current density region. In addition, increasing the gas pressure improves the performance in the entire current density range. The overpotential was separated to discuss these results. The activation overpotential was calculated by Tafel equation, and the concentration overpotential was calculated by subtracting the activation overpotential and the resistance overpotential (= IR) from the total overpotential. Figure 3 shows the results of the activation overpotential and the concentration overpotential at the current density of 2.0 A/cm2. The activation overpotential is reduced at high-temperature and high-pressure. These trends agree with the previous studies. The exchange current density of PBI-MEA increases at high-temperature(1). The oxygen molar concentration become high and the exchange current density is increased at high-pressure(2). On the other hand, the concentration overpotential increases at high-temperature. This is because the air expands at high-temperature and the oxygen’s molar concentration decreases. Although this phenomenon is a major issue in HT-PEFC, the concentration overpotential can be reduced even at high-temperature by increasing the gas pressure.Figure 4 shows the results of I-V characteristics for the three gas flow fields. Here, IR corrected voltage is used to eliminate the influence of the contact resistance due to the flow field structure. Compared to the 2.0 mm pitch straight flow channel, the concentration overpotentials of the 1.0 mm pitch straight flow channel and the porous flow field are reduced. As shown in Figure 5, this is due to improving the oxygen supply under the flow channel ribs(3). Especially, this effect is significant at high-temperature where the oxygen molar concentration is lower. Additionally, in our previous study(4), when using the porous flow field in conventional PEFC (below 100°C), performance degradation due to dry-out was a major issue. However, the porous flow field is useful for HT-PEFC because the polymer electrolyte membrane has low durability against the liquid water and active drainage of generated water is required.AcknowledgementWe would like to thank the Suzuki Foundation in Japan for supporting this study.References(1) A. R. Korsgaad, et al., Journal of Power Sources, 162 (2006).(2) Y. Tabe, et al., Journal of Electrochemical Society, 158 (2011).(3) Y. Iizuka, et al., Journal of Electrochemical Society, 169, (2022).(4) Y. Tabe, et al., Journal of Power Sources, 238, (2013). Figure 1

Study on the Liquid‐Holding Rate Law of Gas–Water–Foam Three‐Phase Flow in a Wavy Pipe

ABSTRACTAs a common method for liquid drainage in wave‐shaped pipelines, foam drainage has been used in gas‐gathering pipelines in various oil and gas fields. One of the common problems encountered in wave‐shaped foam drainage pipelines is the inaccurate prediction of the liquid retention rate. This issue makes it difficult to predict liquid accumulation points, which affects gas output efficiency, causes pipeline corrosion, and generates natural gas hydrates. To clarify the liquid‐holding rate law of wavy foam drainage pipelines is studied. In this study, through experiments to verify the accuracy of the numerical simulation method, we investigate the easiest liquid accumulation points and the liquid‐holding rate of wave‐shaped foam drainage pipelines, with factors such as inlet gas velocity, inlet liquid velocity, import and export differential pressure, undulation angle, and inlet temperature change rule. Among them, the error between the numerical simulation results and the experimental results is 4.68%. Finally, after considering the influence of the aforementioned factors on the liquid retention rate of wave‐shaped pipelines, a new liquid retention rate calculation model for wave‐shaped pipelines with foam drainage is established by introducing dimensionless numbers, such as gas‐phase velocity coefficient, liquid‐phase velocity coefficient, and angle correction coefficient. The method is compared with the results of previous research, and the error is within 15%. The model has a simple form and high calculation accuracy, providing a theoretical basis for pipeline inspectors to predict liquid accumulation conditions and reasonably adjust production schedules.

Unveiling macular displacement: endotamponade variations in retinal detachment repair outcomes.

To compare the rates of macular displacement (MD) in patients with primary macula-off rhegmatogenous retinal detachments (RRD) who underwent pars plana vitrectomy (PPV) with either silicone-oil (SO) or perfluoropropane (C3F8) gas tamponade, and to investigate whether there is a correlation between MD and metamorphopsia. This retrospective comparative study included fifty-three patients with macula-off RRD who underwent a single 25-gauge PPV surgery. The patients were divided into two groups based on the endotamponade used during surgery: 14% C3F8 gas (n=28) or SO (n=25). Demographic information, preoperative, intraoperative, and postoperative characteristics were collected from medical records. Ophthalmological examinations were conducted, and data on various parameters, including perfluorocarbon liquid (PFCL) use, drainage retinotomy, MD rates, and presence of metamorphopsia, were assessed. PFCL was used in all cases, and no patient underwent drainage retinotomy. MD was detected in 18 eyes (64.2%) in the gas tamponade group and 9 eyes (36.0%) in the SO group, and the difference between the two groups was statistically significant (p=0.039). In both groups, 28 patients with suffered from metamorphopsia, but no significant correlation was found between MD and metamorphopsia in the gas group (p= 0.887). The study suggests that MD rates differ significantly between patients who underwent PPV with SO or C3F8 gas tamponade. Furthermore, while MD was observed in both groups, it may not always result in metamorphopsia in most patients after detachment surgery.

Liquid Drainage in the Compaction Process of Asphalt Emulsion Mixtures with Cement

Liquid Drainage in the Compaction Process of Asphalt Emulsion Mixtures with Cement

A simulation study on the influence of marginal pinching upon liquid film dynamics

In fluid dynamics, the generation and bursting of surface bubble liquid films in surfactant-laden environments involve complex phenomena, one of which is marginal pinching at the film's foot—a crucial yet inadequately understood aspect due to experimental limitations. Considering its profound impact on liquid film drainage and lifetime, we utilize high-resolution numerical simulations incorporating a weakly compressible scheme and adaptive mesh refinement to dissect the marginal pinching dynamics with unprecedented detail. Our approach elucidates the pinching dynamics and tracks the evolution of film thickness during the critical late-stage drainage process. By leveraging detailed geometric data from pinched regions, we significantly refine existing drainage models, enhancing their predictive accuracy regarding rupture thickness and film lifetime across various viscosities, surfactant concentrations, and bubble sizes. This refined model demonstrates robust alignment with our simulation results. Furthermore, we establish a quantifiable relationship between the prefactor governing reverse flow induced by the Marangoni effect and surfactant concentration. The methodologies and findings of this study provide foundational knowledge that paves the way for optimized industrial processes and an enhanced understanding of natural phenomena.

Structural evolution and stabilisation mechanism of foam fluids that contain cellulose nanofibres and cellulose nanocrystals: An experimental and theoretical study

Foam fluids are thermodynamically metastable systems, and they evolve over timescales comparable to their time of use, which makes the study of their destabilisation mechanisms crucial for many industrial applications. In our study, foams were made from fluids that contained cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). We explored the effects of nanocelluloses and oils (n-heptane and n-dodecane) on foam stability, bubble coarsening and liquid drainage. Results show that the evolution of the bubble size is strongly slowed by the synergistic effect of CNCs and CNFs, and the structural evolution of foam is greatly impacted. The main responsible mechanism is an increase in local yield stresses due to the presence of CNCs in the foam. The jammed CNCs in foam produce a drainage delay, which makes the foam 50 % drainage time (t50%) of the experimental value deviate by up to 400 % from the classical theory value. When the bubbles coarsen and grow above a threshold size, liquid can drain out of the foam. Finally, a modified model for t50% that considers the drainage delay was proposed. The experimental results validated the proposed correlation and exhibited good reliability and predictive accuracy. The results enable us to elucidate the impact of CNCs and CNFs on the stability of foam fluids.

A time-resolved investigation at multiple-length scales of the structure of liquid foam stabilized by albumins from pea

HypothesisThe structural details of foams made with pea albumins are affected by the pH of the initial solution and followed heat treatment. ExperimentsAn in situ, time-resolved investigation of foams prepared with pea albumins was conducted using small-angle neutron scattering (SANS) in combination with imaging and conductance measurements. Solutions were tested at pH three pH values (3, 4.5, and 8) before and after heating (90 °C for 1 and 5 min). FindingsThe characteristic structures present in the foam from the nano to the meso-scale differed during drainage depending on solution pH. Foams obtained at pH 3, had the largest bubble radius and thinnest plateau border, as well as the highest extent of liquid drainage. At pH 4.5, close to the isoelectric point of the proteins, foams displayed similar bubbles’ behavior to those at pH 8, but with the largest film thickness. In this case, the proteins were extensively aggregated. Heating of the solutions prior to foaming did not significantly affect the foam aging regardless of pH. The quantification of specific surface areas and film thickness over time without sample disruption shows to be a powerful approach to designing foam structures.

Study on the Control of Steam Front Mobility in High-Temperature and High-Salinity Conditions Using Polymer-Enhanced Foam.

This study investigated the enhancing effects of the temperature-resistant polymer Poly(ethylene-co-N-methylbutenoyl carboxylate-co-styrenesulfonate-co-pyrrolidone) (hereinafter referred to as Z364) on the performance of cocamidopropyl hydroxy sulfobetaine (CHSB) foam under high-temperature and high-salinity conditions. The potential of this enhanced foam system for mobility control during heavy oil thermal recovery processes was also evaluated. Through a series of experiments, including foam stability tests, surface tension measurements, rheological assessments, and parallel core flooding experiments, we systematically analyzed the interaction between the Z364 polymer and CHSB surfactant on foam performance. The results indicated that the addition of Z364 significantly improved the strength, thermal resistance, and salt tolerance of CHSB foam. Furthermore, the adsorption of CHSB on the polymer chains enhanced the salt resistance of the polymer itself, particularly demonstrating stronger blocking effects in high-permeability cores. The experimental findings showed that Z364 increased the viscosity of the liquid film, slowed down liquid drainage, and reduced gas diffusion, effectively extending the half-life of CHSB foam and improving its stability under high-temperature conditions. Additionally, in parallel core flooding experiments, the polymer-enhanced foam exhibited significant flow diversion effects in both high-permeability and low-permeability cores, effectively directing more fluid into low-permeability channels and improving fluid distribution in heterogeneous reservoirs. Overall, Z364 polymer-enhanced CHSB foam demonstrated superior mobility control during heavy oil thermal recovery, offering new technical insights for improving the development efficiency of high-temperature, high-salinity reservoirs.

Ultra-stable high-internal-phase emulsions fabricated solely by hydrophilic cellulose nanofiber via inter-droplet jamming

High-internal-phase emulsions (HIPEs) has been increasing interest owing to their large surface area and controllable flow behavior, however, their heavy addition of emulsifiers, e.g., surfactants and surface-active particles, leads to high cost and emulsifier abuse. To solve these issues, we report a new strategy to prepare HIPEs by solely adding a surface-inactive, hydrophilic cellulose nanofiber (CNF). Compared to conventional HIPEs, the highly flocculated CNF is closely packed in the liquid films between oil droplets instead of anchoring at the oil-water interfaces, as referred to the inter-droplet jamming. An efficient jamming behavior is observed at a low CNF concentration (as low as 0.075 wt%) and at very high volume fractions of oil (near 0.85), maintaining the HIPEs over timescales of two years, without the liquid drainage or phase separation. This unexpected stability is mainly attributed to the increase by dozen orders of magnitude in the viscoelasticity of the jammed films as compared with that in the bulk phase, generating a significantly spatial barrier to prevent the depletion attraction between droplets. This simple approach should offer a new pathway to achieve nature-inspired, pure and controlled materials.

The impact of chelating agent pH on the stability and viscosity of CO2 foam under harsh reservoir conditions

The injection of CO2 foam into the carbonate reservoir for enhanced oil recovery (EOR) has attracted special interest in the last decades; nevertheless, the understanding of the effect of liquid solution chemistry on foam stability at high temperatures and salinities is limited. Hence, this paper fully investigates the effect of chelating agents L-glutamic acid-N, N-diacetic acid (GLDA) pH, and hydrochloric acid (HCl) on the stability and viscosity of generated CO2 foam for heterogeneous carbonate formation under reservoir conditions. In this paper, Duomeen TTM and Armovis VES surfactants were utilized due to their capabilities to produce viscous CO2 foam under harsh conditions. The foamability, foam stability, and foam structure were studied at 100 °C and 1000 psi using a high-temperature and high-pressure (HPHT) foam analyzer. The measurement of CO2 foam viscosity was determined at 100 °C, 1000 psi, and 70 % foam quality using the HPHT foam rheometer. Rheology experiments and dynamic light scattering investigated the micelle’s size or aggregation behavior of surfactants. The obtained results showed that the Duomeen TTM generated unstable foam; however, foam stability and foamability improved with the decrease in GLDA pH. Armovis VES showed excellent CO2 foam performance, where the foam half-life time of Armovis VES systems was 240 min. The liquid drainage and bubble coarsening were delayed due to the formation of the viscoelastic liquid phase. The foamability of Armovis VES was improved as the GLDA pH decreased. Furthermore, the addition of HCl to Armovis VES solution presented the highest foamability. The outcomes of the HPHT foam analyzer and HPHT viscometer proved that as the pH of Armovis VES solution decreased, higher foamability was produced. The highest foam viscosity was obtained using the synergic effect of 0.5 wt% Duomeen TTM and 0.5 wt% Armovis VES (39 cp at 100/s). In comparison, 1 wt% Armovis VES presented the lowest foam viscosity (30 cp at 100/s). The outcomes of this research can provide insight into the effect of chemistry on CO2 foam and extend its application in oilfield development. This work broadens the design of novel CO2 foam formulation, leading to the improvement of sweep efficiency in CO2-EOR methods and enhance the gas trapping in carbon storage.

Anomalous diffusion of hydrocarbon vapor through an aqueous foam bubble structure

Hydrocarbons are known as “anti-foamers” because they cause bubble rupture, coalescence, and reduce foaming. We show that the dynamics of bubble structure allows hydrocarbon vapors permeate rapidly when an aqueous foam is placed on a hydrocarbon pool. Two distinct foam layers are formed. Vapor accumulates in an expanding bottom layer at the foam-pool interface where bubbles grow rapidly, rupture, and coalesce. Simultaneously, vapor diffuses through a top layer having small bubble structure, which changes slowly due to Ostwald-ripening. Very little vapor accumulates in the top layer, which has a constant thickness equal to the initial foam thickness. Surprisingly, both accumulation in the bottom layer and diffusion through top layer occur at constant rates, which are independent of time and initial foam thickness. The vapor diffusion rate in the top layer should have decreased, inversely proportional to the initial foam thickness, based on classical diffusion theory; only the fluorosurfactant containing foam (RefAFFF) placed on gasoline follows the classical theory where the bottom foam layer is absent. Therefore, we propose a theory to show a linear increase in diffusion time with initial foam thickness using an effective diffusion-coefficient. Experiments show that this variation could be because of increased liquid drainage, drying, and bubble coarsening, which are not considered explicitly in the theory. We also describe a theory for the expanding bottom layer to show that most vapor formed at the pool surface accumulates for very volatile hydrocarbons. The vapor diffusion controls foam ignition. We show that the measured foam ignition time also increases linearly with initial foam thickness, qualitatively consistent with the predicted diffusion time. By employing different hydrocarbons, we show that the measured foam ignition times decrease inversely proportion to square root of hydrocarbon vapor concentration for a given surfactant. This could be because a surfactant exhibits different degrees of oleophobicity towards different hydrocarbons that can reduce vapor adsorption, solubility, and diffusion at a bubble surface. Different surfactants also exhibit different degrees of oleophobicity towards a given hydrocarbon (n-pentane) and increase ignition times by a factor of six: RefAFFF having the longest ignition time, followed by siloxane-polyoxyethylene formulation, and its individual surfactant components.

The role of nanoparticle–surfactant interactions in air-stabilized foams used for improving oil recovery

Foam flooding, an emerging tertiary oil recovery technique, demonstrates efficacy as a conformance control method in enhanced oil recovery. Conformance control mitigates injected displacement fluid channeling and bypassing, improving macroscopic sweep efficiency. Generated foamed films preferentially enter high permeability zones, diverting subsequent injection into unswept lower permeability regions. Nanoparticle-reinforced foams exhibit consistent bulk stability and effective residual oil mobilization. This work utilizes dynamic foam analysis to probe the synergistic effects of zinc oxide nanoparticles and anionic surfactant on foam generation and persistence. Bulk and local scale foam stability is evaluated under various potassium chloride concentrations. Optimal foam stability occurs near the critical micelle concentration of the surfactant at 2,500 ppm. Increasing electrolyte concentration within a fixed surfactant formulation decreases foam stability due to salt-induced micellar swelling. An optimized electrolyte and nanoparticles with a surfactant combination produce high-quality foam with increased bubble density per unit area. Micellar swelling by nanoparticle adsorption inhibits lamellae thinning and liquid drainage. Enhanced foam properties improve microscopic displacement efficiency and mobility control in foam-assisted oil recovery. Oil recovery is increased by approximately 22% compared to conventional waterflooding.

Measurement of air-water counter-current flow rates in vertical annulus using multiple differential pressure signals and machine learning

Abstract Gas–liquid counter-current flow in vertical annulus is involved in several industrial fields such as petroleum engineering. For example, in coalbed methane wells with liquid pump drainage, obtaining the real-time flow rate of gas–liquid two-phase in the annulus is crucial for the development management of coalbed methane wells. However, due to complex flow conditions, this demand is difficult to achieve through traditional flow metering means. Therefore, this paper proposes a flow prediction method based on multi-group differential pressure signals and machine learning technology. Air-water two-phase flow experiments were carried out on a vertical annulus pipeline with inner and outer diameters of 75 mm/125 mm and adjustable eccentricity. The probability density function and power spectrum density of 3 groups of differential pressure signals collected at different height intervals in the annulus were used as model inputs. A gas–liquid two-phase flow prediction model was constructed based on the artificial neural network model, and the model hyper-parameters were optimized using Bayesian optimization. The results show that on the 440-group test dataset under the combined conditions of air superficial velocity of 0.06–5.04 m s−1, water superficial velocity of 0.03–0.25 m s−1, and pipeline eccentricity of 0, 0.25, 0.5, 0.75, 1, etc. This model can achieve average prediction errors of 9.12% and 29.34% for gas and water flow rates respectively. This method can be applied to the non-throttling, non-invasive measurement of phase flow rate under the condition of annulus air-liquid counter-current flow.

Chitosan/carbomer nanoparticles- laden in situ gel for improved ocular delivery of timolol: in vitro, in vivo, and ex vivo study.

Due to the small capacity of the eye cavity and the rapid drainage of liquid into the nasolacrimal duct, patients must frequently administer the drops. Nanoparticles (NPs) and in situ gel systems have each proven their ability to achieve eye retention independently. In this study, timolol-loaded chitosan-carbomer NPs were prepared using the polyelectrolyte complexation method, and incorporated into a pH-responsive in situ gel system made of carbomer. The rheological behavior of NPs-laden in situ gel was examined at room and physiological conditions. Characteristics such as zeta potential, surface tension, refractive index, mucoadhesive properties, drug release, transcorneal permeability, and intra-ocular pressure (IOP) lowering activity were investigated on NPS and NPs-laden in situ gel formulations. The optimum gained NPs system had an encapsulation efficiency of about 69% with a particle size of 196nm. The zeta potential of the NP and NPs-laden in situ gel were - 16 and + 11 mV respectively. NPs-laden in situ gel presented enhanced viscosity at physiological pH. All physicochemical properties were acceptable for both formulations. NPs and NPs-laden in situ gel systems proved to sustain drug release. They showed mucoadhesive properties which were greater for NPs-laden in situ gel. IOP reduction by NPs-laden in situ gel was significantly higher and more long-lasting than the timolol solution and NPs. In conclusion, the developed NPs-laden in situ gel is a promising carrier for ocular drug delivery due to the slow release of drug from nanoparticles, its mucoadhesive properties, and high viscosity acquisition in contact with precorneal film, which lead to improved therapeutic efficacy.

Impact of microplastic pollution on breaking waves

Anthropogenic plastic waste heavily pollutes global water systems. In particular, micron-sized plastic debris can have severe repercussions for the ocean flora and fauna. Microplastics may also affect physical processes such as wave breaking, which are critical for air–sea interaction and albedo. Nevertheless, the effects of micron-sized plastic debris on geophysical processes are widely unexplored. Herein, we investigate the effect of microplastic collected from the North Pacific and a surfactant mimicking surface active materials present in the ocean on the stability of foam generated by breaking wave experiments. We found that microplastic particles increase foam stability. In particular, an increased foam height was found in a column foaming setup, while an increased foam area was observed in a laboratory-scale breaking wave channel. We propose that microplastic particles assemble at the air–water interface of foam bubbles, form aggregates, presumably decrease the liquid drainage in the liquid film, and thus change the lifetime of the liquid film and the bubble. The effect of surfactants is generally larger due to their higher surface activity but still in a range where synergistic effects can be observed. Our results suggest that microplastic could influence oceanic processes essential for air–sea interaction, sea spray formation, and albedo.

Bipolar Plate Design Assessment: Proton Exchange Membrane Fuel Cell and Water Electrolyzer

ABSTRACTProton exchange membrane fuel cells (PEMFCs) as power generators and proton exchange membrane water electrolyzers (PEMWEs) as hydrogen fuel producers play critical roles in implementing hydrogen energy. The bipolar plates (BPPs) in both PEMFC and PEMWE facilitate the distribution of reactants and products, providing electrical connectivity in a series of singular cells. Although both systems are categorized under the same PEM spectrum, the differing reaction mechanisms require specialized plate properties to achieve optimum performance. This short review analyzes the characteristics of BPPs in both PEMFC and PEMWE, with a focus on the plate material, coating, and flow field. This short review concluded that the polymer composite graphite–based BPPs are the most feasible for PEMFC with no coating needed. PEMWE needs SS316 as a BPP material with a conductive coating to withstand the highly corrosive oxygen evolution reaction at the anode. The serpentine flow field showed dominance in PEMFC stack performance due to even fluid distribution and efficient liquid water drainage. However, its high‐pressure drop contributes to greater parasitic power. PEMWEs commonly adopt the parallel flow field for its lower contact resistance and bubble formation for efficient mass transport toward the cathode.

Radial bubble size distributions in a rising foam column

The diameter distribution of bubbles in foam is one of the most important features in foam-based separation processes like foam fractionation and froth flotation.In this study the bubble size at different radial positions of pneumatically produced foams without coalescence and coarsening of bubbles is investigated in a cylindrical column by employing an invasive sampling probe. It is shown that pronounced differences of the local Sauter-mean diameter of the bubbles can appear in radial direction. Oftentimes a parabolic profile with the largest mean bubble diameter in the center of the column is found. The difference of the Sauter-mean diameter between wall- and center region is in the order of up to 60%. Experiments on foams produced with different spargers, gas flow rates and liquid filling levels reveal that the actual degree of the inhomogeniety depends on the specific bubble size distribution that is produced by the sparger, and becomes more pronounced if the range of bubble diameters in the foam increases. As an explanation for the observations, hydrodynamic interactions in the liquid phase, as well as the behavior of different sized bubbles close to the liquid/foam interface are proposed.The observed existence of local differences of the bubble diameters can have a strong influence the dynamic behavior, like liquid drainage, and measurement methods of pneumatic foams. In particular it can limit the applicability of surface-based bubble size measurements.