Mechanistic understanding of the modes of action of foam control agents

Antifoams in non-aqueous diesel fuels: Thin liquid film dynamics and antifoam mechanisms

HypothesisFoaming in diesel fuels is not well understood and leads to operational challenges. To combat deleterious effects of foaming, diesel formulations can include additives called antifoams. Existing antifoams, unfortunately, are inherently ash-generating when combusted, with unknown environmental impacts. They are prohibited in certain countries, so identifying effective alternative ash-free antifoam chemistries is needed. ExperimentsWe conduct systematic characterization of foam stabilization and antifoaming mechanisms in diesel for two different antifoams (silicone-containing & ashless chemistries). Employing a custom technique combining single-bubble/single-antifoam-droplet manipulation with white light interferometry, we also obtain mechanistic insights into foam stability and antifoam dynamics. ResultsCoalescence times from both bulk foam and single bubble experiments confirm ashless antifoams are effective at reducing foaming, demonstrating the potential of ashless antifoams. Further, we perform single-antifoam-droplet experiments and obtain direct experimental evidence revealing the elusive antifoaming mechanisms. Interestingly, the silicone-containing and ashless antifoams seemingly function via two different mechanisms: spreading and dewetting respectively. This surprising finding refutes conventional wisdom that spreading is likely the only antifoam mechanism in diesels. These results and the reported experimental framework significantly enhance the scientific understanding of non-aqueous foams and will accelerate the engineering of alternative antifoam chemistries for non-aqueous systems.

Preparation of hyperbranched hydrophobic nano-silica and its superior needling-effect in PDMS defoam agent

Hydrophobic nano silica powder is a kind of important synergist to silicone defoaming agents. The large pore volume and branched chain conformation of silica nanoparticles present superior effects on defoaming properties. However, silica nanoparticles synthesized by liquid phase easily aggregate and pore collapse because of their high surface activity and polarity, leading to poorer dispersity and limited practicability. In this paper, a novel hydrophobic silica with a hyperbranched structure was designed through in-situ modifying method with hexamethyldisilazane (HMDS) and polydimethylsiloxane (PDMS) in the liquid phase. The trimethylsilanol generated by HMDS hydrolysis reacts quickly with the highly active hydroxyl groups on the silica, causing the surface properties of the nanoparticles to transform from polar to non-polar properties. The steric hindrance of the trimethyl silicon and the reduction of the surface polarity effectively prevent silica pores from collapsing and maintain the macropore structures to realize the hyperbranched silica. At the same time, the -Si (CH3)2- from PDMS endowed the hyperbranched silica with excellent hydrophobicity. When applied in the defoaming agent, the hydrophobicity of silica contributes to dewetting the foams, and the hyperbranched spatial structures play an enhanced needling effect. Therefore, this hydrophobic hyperbranched silica exhibited a surprising defoaming effect, which significantly reduced the defoaming time from 464.4 s to less than 2 s, superior to commercial defoaming silica (155.3 s). The defoaming efficiency reached 100 % within 2 s of the end of the shaking, and the defoamer antifoaming ability was improved to reach 27.5 min, which was 77 % higher than that of commercial defoamer.

Effects of food waste hydrolysate as an external carbon source on defoaming in wastewater treatment with activated sludge process

The activated sludge process is the most widely used technology for treating municipal wastewater. However, thick foam often occurs in activated sludge process. Here, we reported for the first time the effect of food waste hydrolysate (FWH) as an external carbon source on defoaming in activated sludge process. The study found that FWH was effective in defoaming at a wide dose range of 50-1600 mg/L total solids, as exhibiting that the foaming tendency of FWH-added foam mixed liquor was reduced to 0 mL-foam/mL-air·min from initial 0.171 mL-foam/mL-air·min in the control without adding FWH with 100 % of defoaming efficiency. Fatty acids, oils, and solid particles in FWH jointly contributed to the deformation. Among these factors, the concentration of long-chain unsaturated fatty acids was mainly responsible for the defoaming. This work provides a cost-effective strategy to solve the foaming problem in activated sludge process as well as providing external carbon sources.

Surfactant foam injection for remediation of diesel-contaminated soil: A comprehensive study on the role of co-surfactant in foaming formulation enhancement

Aqueous foam injection is a promising technique for in-situ remediation of soil and aquifers contaminated by petroleum products. However, the application efficiency is strongly hindered by foam's instability upon contact with hydrocarbons. Addressing this, we propose a new binary surfactant mixture of Sodium Dodecyl Sulfate (SDS) and Cocamidopropyl Hydroxysultaine (CAHS). This study investigates CAHS's role as a co-surfactant in enhancing foam stability against antifoaming diesel oil under static and dynamic conditions. Using a dynamic foam analyzer (DFA-100), we assessed static foam's stability by monitoring decay profiles and bubble growth over time. The results revealed that the highest stability can be reached at a CAHS to SDS ratio of 50:50, increasing the half-life of the foam by 7.7 times. Remarkably, our analyses at bulk and bubble scales also elucidated the mechanisms behind the enhanced foam stability of the proposed binary surfactant mixture in the absence and presence of diesel. Additionally, in a 1D sand column, the SDS-CAHS mixture demonstrated more than twofold improvement of the Resistance Factor, attributed to the better survival of the lamellae due to the reduced rate of their destruction. This formulation also yielded a recovery improvement of >10 % compared to SDS foam. The significant improvements in stability and performance of the SDS-CAHS (50:50) mixture were credited to a robust pseudo-emulsion film formation, creating a higher oil entry barrier. This reinforcement and the surfactant molecules' synergistic interactions at the gas-liquid-oil interface significantly contributed to the overall effectiveness.

Effects of residual foaming agent and defoamer on defoaming-flocculation-filterpress characteristics of earth pressure balance shield muck

Foaming agents as a combination of several components are usually used as soil conditioning during earth pressure balance shield (EPBS) tunnelling. These residues in waste EPBS muck lead to a series of new challenges for in-situ recycling, i.e., foams overflow flocculation tank. This study investigates the effects of residual foaming agent components and defoamers on defoaming-flocculation-filterpress characteristics of EPBS muck using an improved flocculation and filterpress system. Residual foam height (Hf), defoaming ratio (DFR), antifoaming ratio (AFR), total suspended substance (TSS), turbidity, moisture content (MC), and zeta potential (ZP) were selected as characterization indices. The microstructure of filterpress cakes was analyzed using a scanning electron microscope. Results demonstrate that an enhancement within 0.0-1.0wt.% for sodium fatty alcohol polyoxyethylene ether sulfate (AES) and alpha olefin sulfonate (AOS) significantly reduces DFR and AFR. The MC and ZP decline, while the Hf and turbidity enhance. The combinations of nonionic surfactants alkyl polyglycoside (APG) and fatty alcohol-polyoxyethylene ether (AEO) in a concentration range of 0.0-1.0wt.% with 0.2wt.% AES causes the Hf, DFR, AFR, turbidity, and ZP to exhibit absolutely different variations. The MC with the growth in both APG and AEO presents a trend of first decreasing and then increasing. By increasing foam stabilizers sodium carboxymethyl cellulose (CMC) and guar gum (GG) within 0.02-0.10wt.%, the AFR, TSS, and ZP enhance in varying degrees, while the Hf, DFR, and MC gradually reduce. With the increase of defoamers hydroxyl silicone oil-glycerol polyoxypropylene ether (H-G) and dimethyl silicone oil-glycerol polyoxypropylene ether (D-G) within 0.002-0.010wt.%, the DFR and AFR are significantly improved, while the TSS, turbidity, MC, and ZP display varying degrees of reduction. Moreover, defoaming-flocculation-filterpress mechanisms of EPBS muck are explored to provide a useful reference for actual in-situ recycling projects.

An experimental study of foam-oil interactions for nonionic-based binary surfactant systems under high salinity conditions

A key factor affecting foam stability is the interaction of foam with oil in the reservoir. This work investigates how different types of oil influence the stability of foams generated with binary surfactant systems under a high salinity condition. Foam was generated with binary surfactant systems, one composed of a zwitterionic and a nonionic surfactant, and the other composed of an anionic and a nonionic surfactant. Our results showed that the binary surfactant foams investigated are more tolerant under high salinity conditions and in the presence of oil. This was visually observed in our microscopic analysis and was further attributed to an increase in apparent viscosity achieved with binary surfactant systems, compared to single surfactant foams. To understand the influence of oil on foam stability, we performed a mechanistic study to investigate how these oils interact with foams generated with binary surfactants, focusing on their applicability under high salinity conditions. The generation and stability of foam are linked to the ability of the surfactant system to solubilize oil molecules. Oil droplets that solubilize in the micelles appear to destabilize the foam. However, oils with higher molecular weights are too large to be solubilized in the micelles, hence the molecules will have less ability to be transported out of the foam, so oil seems to stabilize the foam. Finally, we conducted a multivariate analysis to identify the parameters that influenced foam stability in different oil types, using the experimental data from our work. The results showed that the oil molecular weight, interfacial tension between the foaming liquid and the oil, and the spreading coefficient are the most important variables for explaining the variation in the data. By performing a partial least square regression, a linear model was developed based on these most important variables, which can be used to predict foam stability for subsequent experiments under the same conditions as our work.

Microscopic Understanding of Interfacial Performance and Antifoaming Mechanism of REP Type Block Polyether Nonionic Surfactants

In many practical applications involving surfactants, achieving defoaming without affecting interfacial activity is a challenge. In this study, the antifoaming performance of REP-type block polymer nonionic surfactant C12EOmPOn was determined, and molecular dynamics simulation method was employed to investigate the molecular behaviors of surfactants at a gas/water interface, the detailed arrangement information of the different structural segments of the surfactant molecules and the inter-/intra-interactions between all the structural motifs in the interfacial layer were analyzed systematically, by which the antifoaming mechanisms of the surfactants were revealed. The results show that the EO and PO groups of REP-type polyether molecules are located in the aqueous phase near the interface, and the hydrophobic tails distribute separately, lying almost flat on the gas/water interface. The interaction between the same groups of EOs and POs is significantly stronger than with water. REP block polyethers with high polymerization degrees of EO and PO are more inclined to overlap into dense layers, resulting in the formation of aggregates resembling "oil lenses" spreading on the gas/water interface, which exerts a stronger antifoaming effect. This study provides a smart approach to obtaining efficient antifoaming performance at room temperature without adding other antifoam ingredients.

On recycling earth pressure balance shield muck with residual foaming agent: defoaming and antifoaming investigations

Earth pressure balance (EPB) shield is increasingly employed in metro tunnel construction, and causes a series of environmental, safety, and resource waste problems due to the disposal of a considerable amount of muck. In situ recycling of EPB shield muck is an effective solution, whereas the foam is generated by residual foaming agents used as the muck conditioning material during tunnelling, which often adsorbs clay particles and overflows the flocculation tank. To achieve defoaming and antifoaming during the reuse of muck, this study prepared novel eco-friendly silicone oil-polyether defoamers by condensation, compounding, and shear emulsification. Defoaming and antifoaming performances of different defoamers were tested using a modified Ross-Miles method and a scale model of field flocculation systems. The results indicated that a high efficiency in defoam and antifoam was characterized by chemical grafting of nano-SiO2 from silicone oils, uniform distribution and large size of grains, low viscosity, and surface tension. The defoamer dosage of 0.002-0.004 wt% near critical micelle concentration (CMC) for each defoamer is reasonable. Overall, the prepared hydroxyl silicone oil-glycerol polyoxypropylene ether (H-G) defoamer compared with other silicone oil-polyether defoamers and commercial defoamers presents the highest defoaming and antifoaming efficiency. Considering the effects of EPB shield muck, the H-G defoamer is least affected by the compound materials and increasing concentration of the commercial foaming agent. Nevertheless, the stability of the H-G emulsion system is weaker than that of the dimethyl silicone oil-glycerol polyoxypropylene ether (D-G) emulsion system after 1 month of sealed storage.

Multibranched Molecule Defoamers Based on Methyl Gallate for Highly Effective Defoaming and Antifoaming

Bubbles or foams appear in many industrial processes, bringing inconvenience; yet, efficient capture or removal of them is still challenging. In this study, we report the synthesis and properties of multibranched molecule defoamers based on methyl gallate derivatives (Mb-GDs), which adopt methyl gallate (M-G) as the parent structure, by incorporating alkyl groups from alkyl isocyanates (A-I) with different chain lengths (C12 and C18) to replace R-OH in the M-G structure and further by linking two Mb-GDs into one Gemini-type multibranched derivative (Gt-Mb-GD) by transesterification to construct a defoamer material with a larger spatial volume. The surface properties and interfacial activity of molecular defoamers in aqueous solutions were studied, and the structure-property relationships of the multibranched gallate molecule defoamers based on Mb-GDs and Gt-Mb-GDs were further investigated by comparing the defoaming and antifoaming performance in four typical surfactant foams and foaming solutions with two kinds of commercial defoamers. The foam experiments indicated that the defoamers with a longer branched chain length (C18) showed more effectiveness in defoaming and antifoaming for four surfactant foams or foaming solutions, even at very low dosages, which were far stronger than the commercial high-carbon alcohol defoamer with a linear structure and comparable to branched silicone-based emulsion-type defoamers. Compared with Mb-GD defoamers, Gt-Mb-GD defoamers with a larger branched structure showed a higher defoaming performance. The study found the great potential of materials with multibranched structures for practical applications as the core components of high-performance defoamers.

Effect of Shear on Pumped Capillary Foams

Foam flow in many applications, like firefighting and oil recovery, requires stable foams that can withstand the stress and aging that result from both shear and thermodynamic instability. Events of drainage and coarsening drive the collapse of foams and greatly affect foam efficacy in processes relying on foam transport. Recently, it was discovered that foams can be stabilized by the synergistic action of colloidal particles and a small amount of a water-immiscible liquid that mediates capillary forces. The so-called capillary foams contain gas bubbles that are coated by a thin oil-particle film and integrated in a network of oil-bridged particles; the present study explores how this unique architecture impacts the foams' flow dynamics. We pumped capillary foams through millimeter-sized tubing (ID: 790 μm) at different flow rates and analyzed the influence of stress and aging on capillary foam stability. We find that the foams remain stable when pumped at higher flow rates but undergo phase separation when pumped at low flow rates. Our observations further show that the particle network is responsible for the observed stability in capillary foams and that network strength and stability of an existing foam can be increased by shearing.

Compressive Strength of Acrylic Polymer-Stabilized Kaolinite Clay Modified with Different Additives

Although numerous studies have shown the successful use of acrylic-based polymers as one of the chemical substances to improve soil mechanical behavior, their basic ingredients in commercial products are not revealed due to the manufacturers' confidential policy. Among them, additives including pH control agents, thickeners, antifoams, and wetting agents are widely well-known owing to their enhancement effects on different properties of polymers. However, the effect of additives on the soil-polymer mixture is not completely investigated. Therefore, in this study, some of the frequently used additives in acrylic polymers were selected to investigate the effects of each one on the compressive strength of clayey soil. These additives include xanthan gum, Tylose, and carboxymethyl cellulose (CMC) as thickeners, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and Kenon 10 as wetting agents, an ether-based antifoaming agent, and ammonia solution as a pH control agent. A combination of each additive (between 0 and 5% by weight) and polymethyl methacrylate-co-butyl acrylate (with 5% by weight) was added to kaolinite soil to measure the variation of unconfined compressive strength (UCS) and the stress-strain behavior of the soil-polymer-additive mixture. The results indicated that thickeners significantly affected the unconfined compressive strength up to 248% and increased the ductility of the stabilized samples. Acidic pH of the emulsion led to higher unconfined compressive strength of the stabilized soil up to 2.33 times that with alkaline. It is also demonstrated that the use of a higher amount of anionic wetting agent resulted in higher failure strain and lower unconfined compressive strength.

Foaming mechanisms and control strategies during the anaerobic digestion of organic waste: A critical review

Foaming is a problem that affects the efficient and stable operation of the anaerobic digestion process. Characterizing foaming mechanisms and developing early warning and foaming control methods is thus critically important. This review summarizes the correlation of process parameters, state parameters, and microbial communities with foaming in anaerobic digesters; discusses the applicability of the above-mentioned multi-scale parameters and foaming potential evaluation methods for the prediction of foaming risk; and introduces the principles and practical applications of antifoaming and defoaming methods. Multiple causes of foaming in anaerobic digestion systems have been identified, but a generalizable foaming mechanism has yet to be described. Further study of the correlation between extracellular polymeric substances and soluble microbial products and foaming may provide new insights into foaming mechanisms. Monitoring the foaming potential (including the volume expansion potential) is an effective approach for estimating the risk of foaming. An in-situ monitoring system for determining the foaming potential in anaerobic digestion sites could provide an early warning of foaming risk. Antifoaming methods based on operating parameter management and process regulation help prevent foaming from the source, and biological defoaming methods are highly targeted and efficient, which is a promising research direction. Clarifying foaming mechanisms will aid the development of active antifoaming methods and efficient biological defoaming methods.

Foam-Resilient Distillation Processes—Influence of Pentosan and Thermal Energy Input on Foam Accumulation in Rye Mash Distillation

Foaming of mashes during distillation is a common problem encountered in spirit drink production. It has a negative impact on the purity of the final product. This research article presents the key aspects of foam accumulation in rye mashes during distillation. Foam accumulation was influenced by substrate characteristics and process parameters. The experiments showed that pentosan levels and thermal energy input were the crucial parameters for foam accumulation in rye mashes. Foam accumulation was significantly enhanced by higher pentosan levels, due to the higher viscosity imparted by pentosan. Hence, degradation of pentosans prior to distillation presents a way to reduce foam accumulation. In terms of thermal energy input, foam accumulation was significantly lower when the thermal energy input was reduced from 400 to 200 W/L. Substantial foaming only occurred in a narrow temperature range of 89.5 to 98.2 C. The results allowed for the first time to make recommendations to prevent problematic foam accumulation during distillation of rye mashes.

Preparation of Silicone Emulsion Defoamer with Easy Separation of Magnetic Hydrophobic Nanoparticles

To prepare lyophobic magnetic nanoparticles (LMNs) with core/shell structure to be applied in silicone emulsion defoamer, magnetic nanoparticles covered with silica (MNS) were prepared in a one-step process from FeCl3 · 6H2O, FeCl2 · 4H2O and tetraethyl orthosilicate and then modified with poly (methylhydrosiloxane). X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscope (FTIR), thermogravimetric analysis (TGA), and contact angle tests were performed to characterize the nano-particles, and the droplets of the defoamer emulsion were observed with a microscope. The foam breaking and foam inhibition properties of the defoamer and the magnetic separation of the particles were observed and recorded by a camera. It was found that the silicone emulsion defoamer exhibited good foam breaking and foam inhibition properties for foaming systems with anionic, cationic and non-ionic surfactants, respectively. The solid particles in the defoamer could be easily separated from the defoamed systems by a magnet.

Dynamics and mechanism of liquid film collapse in a foam

Foams have unique properties that distinguish them from ordinary liquids and gases, and are ubiquitously observed in nature, both in biological systems and industrial products. Foams are known to eventually collapse over time; given their wide-range industrial application, understanding how bubbles in a foam collapse is an important aspect for product longevity and tailoring physical properties. Previously, it was shown that droplets are emitted during the collective bubble collapse, however the mechanism of the droplet emission in a foam is not yet clearly understood. It is directly related to the stability of the foam, thus we quantitatively investigate collapse dynamics in liquid films in a foam, and identify some unique features. When one film breaks, we see that the oscillation of the vertical Plateau border to which it is connected induces anomalous liquid transport from the edge of the border to the center. Once a crack appears near the border and a collapse front is formed, we find that the curvature of the front reverses as it migrates, followed by the emergence and emission of droplets. We elucidate the origins of this behavior and discuss the stability of foams, establishing how the characteristic time scales of the process relate to each other.

Influence of Foam Characteristics on the Aviation Coolants' Pollution Degree

The particulate contamination degree of aviation coolants (ACs) is overestimated commonly because the bubbles in ACs are erroneously recognized as particulate contaminants during the measurement process. In this work, the factors that influence the foam behavior and contamination degree of ACs are investigated. It is evidenced that the foam behavior of ACs is basically unaffected by the ratio of glycol to water of the base solution, which, however, is highly influenced by the organic additive. Also, the more the organic additive arranged at the gas-liquid interface, the lower the surface tension of glycol aqueous (GA) solution and the higher the contamination degree. Furthermore, the foam characteristics and contamination degree of ACs are highly affected by the working conditions, such as airflow, operating temperature, and gas pressure. Besides, the defoaming rate can be accelerated by adding an antifoaming agent or ultrasonic processing; however, the defoaming effect of the natural static method and pressuring positively treatment is disappointing. To further improve the defoaming effect, several efficient synergetic methods of defoaming have been proposed.

Challenges and future of chemical assisted heavy oil recovery processes

The primary method for heavy oil and bitumen production across the world is still in-situ steam-based technology. There are some drawbacks associated with steam-driven heavy oil recovery methods such as cyclic steam stimulation (CSS), steam flooding, and steam-assisted gravity drainage (SAGD). These cons include the high greenhouse gas footprint, low heavy oil/bitumen recovery, and difficulty in stop operation in emergency conditions. There exists a need for an improved method for recovering residual oils after applying steam injection. One of the potential technologies for doing this is chemical assisted heavy oil recovery, especially alkaline and surfactant additives. But the challenging question is how to develop a chemical-based oil recovery method considering long-term steam-rock interactions. Several associated issues of chemical additives, including adsorption behavior of surfactant at reservoir conditions and thermal stability of surfactant at steam chamber temperature, make this question more complex. This paper addresses all these concerns and provides solid knowledge regarding this technology. We delve into newly formulated chemicals for coupling with thermal oil recovery techniques that are still limited to lab-scale research, with the need for further studies. This critical review also provides the opportunities and challenges associated with chemical assisted heavy oil/bitumen production in a post-steam injection scenario. Finally, different aspects of such a method are covered in this review, along with practical information on field trials and best practices across the world.

Controlling the lifetime of antibubbles

An antibubble is a liquid droplet wrapped by a thin layer of gas, inside a bulk liquid usually of the same composition. The lifetime of an antibubble is governed by the drainage of the gas between the two liquid-gas interfaces populated by surfactants. Depending on the relative magnitude of surface viscosity and elastic moduli, which directly depend on or are determined by the nature of surfactants, the lifetime of an antibubble may vary a lot, from few seconds to few minutes. While such a difference can be predicted with models that include the role of interfacial properties, they were not observed experimentally in previous studies, due to important sources of dispersion. In this review, the main sources of dispersion are identified, such as (i) the initial amount of gas embedded in the antibubble, (ii) the level of saturation of gas in the bulk liquid, (iii) the presence of dust particles (<0.5 μm) in the gas, and (iv) three-dimensional flow effects. By accounting for these various effects, we obtain a coherent view on the lifetime of an antibubble, as a function of its radius and the surface rheology, with excellent consistency between experiments and modeling. Results thus demonstrate that controlling the size and lifetime of antibubbles is achievable.

In-situ observation of collective bubble collapse dynamics in a quasi-two-dimensional foam

The stability of foams is an important subject not only for fundamental science, but for applications in daily life. The most destructive phenomenon underpinning foam collapse is a collective bubble collapse, yet the mechanism behind this is unclear. In this study, we clarify the dynamics of the collective bubble collapse in a quasi-two-dimensional foam by in-situ observation with a high speed camera. We find two modes for collective bubble collapse: one is the propagation of liquid film breakage via impact with the stream of another broken liquid film. The other is breakage of a distant liquid film due to penetration by a liquid droplet, emitted by impact with the flow of a broken liquid film. As the liquid fraction increases, the velocity of liquid droplets decreases. Instead of penetration, the liquid droplet bounces like a billiard ball or it is absorbed into other films.

Spreading of Oil-in-Water Emulsions on Water Surface

This work presents the spreading behavior of oil-in-water (o/w) emulsions on the water surface recorded using a high-speed photography method. We study a series of o/w emulsions with two different droplet sizes of 4.50 and 0.75 μm and volume fractions of the oil phase in the 20-80% range. Results show that for all the emulsions a rapid spreading occurs upon the collision with the water surface, which then forms a thin film expanding with time. Appearance of a dry spot in the center of collision is observed in the spreading of the emulsions in midvolume fraction range that induces a bursting-like spreading. For the highly concentrated emulsions, the deliberation of decompression energy from the deformed oil phase droplets inhibits the bursting, increases the equilibrium propagation radius, and reduces the dissipation time. The role of viscoplasticity (existing of the yield stress) is considered and a model describing the propagation step of the emulsion spreading is presented. The model shows that the peculiarities of the spreading are determined by the competition between yielding, plastic viscosity, and interfacial tension. By comparing the model prediction and experimental results, it is suggested that the spreading behavior of the emulsions is not only a consequence of the surface tension gradient but also the coalescence of the oil droplets during spreading.

Achieving foaming control smartly: pre-solubilized flavor oil serves as an in situ homogeneous defoamer

In the wide application of aqueous foam, creating abundant foam and processing appropriate foaming control are both essential, depending upon the actual situation; the latter process is not only harder to achieve, but also more complicated to comprehensively understand on the molecular level. In this paper, a type of natural flavor oil, carvone, was solubilized in a micelle solution of sodium dodecyl sulfate (SDS) to study the effect on the foaming properties. The foamability and foam stability of the swollen micelle solutions were experimentally characterized, and the molecular behavior of the surfactant and oil molecules before, during and after the foaming process were investigated. It was found that the solubilized carvone co-adsorbed with SDS at the gas/water interface and caused a prominent effect on the foam film stability in several approaches, thereby making the flavor oil a possible foam controller that would not inhibit foam formation, but could eliminate foam efficiently once foam was undesired. Interestingly, it was found that the release of flavor in the foaming process was promoted. Detailed discussion of the interfacial behavior of carvone and the effect on the foaming properties of surfactants in different stages of foam may provide a theoretical foundation for exploring green and smart approaches in achieving foaming control.

Playing with Emulsion Formulation to Control the Perforation of a Freely Expanding Liquid Sheet

A single-drop experiment based on the collision of one drop of liquid on a small solid target is used to produce liquid sheets that are visualized with a fast camera. Upon impact, the drop flattens into a sheet that is bounded by a thicker rim and radially expanding in air. Emulsion-based liquid sheets are destabilized through the nucleation of holes that perforate the sheet during its expansion. The holes grow until they merge together and form a web of ligaments, which are then destabilized into drops. We propose the perforation mechanism as a sequence of two necessary steps. The emulsion oil droplets first enter the air/water interface, and then spread at the interface. We show that the formulation of the emulsion is a critical parameter to control the perforation as the addition of salt or amphiphilic copolymers can trigger or completely inhibit the perforation mechanism. We demonstrate that the entering of the droplets at the air/water interface is the limiting step of the mechanism. Thin-film forces such as electrostatic or steric repulsion forces stabilize the thin film formed between the interface and the approaching oil droplets, thus preventing the entering of droplets at the interface and in turn inhibiting the perforation process. We theoretically rationalize the successive steps in the approach and entering of an oil droplet at the film interface and the role of salt and amphiphilic polymer in the different steps.

Bubble Meets Droplet: Particle-Assisted Reconfiguration of Wetting Morphologies in Colloidal Multiphase Systems

Wetting phenomena are ubiquitous in nature and play key functions in various industrial processes and products. When a gas bubble encounters an oil droplet in an aqueous medium, it can experience either partial wetting or complete engulfment by the oil. Each of these morphologies can have practical benefits, and controlling the morphology is desirable for applications ranging from particle synthesis to oil recovery and gas flotation. It is known that the wetting of two fluids within a fluid medium depends on the balance of interfacial tensions and can thus be modified with surfactant additives. It is reported that colloidal particles, too, can be used to promote both wetting and dewetting in multifluid systems. This study demonstrates the surfactant-free tuning and dynamic reconfiguration of bubble-droplet morphologies with the help of cellulosic particles. It further shows that the effect can be attributed to particle adsorption at the fluid interfaces, which can be probed by interfacial tensiometry, making particle-induced transitions in the wetting morphology predictable. Finally, particle adsorption at different rates to air-water and oil-water interfaces can even lead to slow, reentrant wetting behavior not familiar from particle-free systems.

Preparation and characterization of lidocaine rice gel for oral application

The objective of the present study was to prepare buccal anesthetic gels using rice as gelling agent. Rice grains of four rice varieties, Jasmine (JM), Saohai (SH), Homnil (HN), and Doisket (DS) were chemically modified. Buccal rice gels, containing lidocaine hydrochloride as local anesthetic drug were formulated using the respective modified rice varieties. The gels were evaluated for outer appearance, pH, color, gel strength, foaming property, adhesion, in vitro drug release and in vivo efficacy. It was found that the developed rice gels possessed good texture. Rice varieties showed influence on gel strength, color, turbidity, adhesive property, release property, and anesthetic efficacy. JM gel showed the lowest turbidity with light transmission of 86.76 ± 1.18% whereas SH gel showed the highest gel strength of 208.78 ± 10.42 g/cm(2). Lidocaine hydrochloride can cause a decrease in pH and adhesive property but an increase in turbidity of the gels. In vitro drug release profile within 60 min of lidocaine SH gel and lidocaine HN gel showed that lidocaine could be better released from SH gel. Evaluation of in vivo anesthetic efficacy in 100 normal volunteers indicates that both lidocaine rice gels have high efficacy but different levels. Lidocaine SH gel possesses faster onset of duration and longer duration of action than lidocaine HN gel.

Filler functionality in edible solid foams

We review the functionality of particulate ingredients in edible brittle foams, such as expanded starchy snacks. In food science and industry there is not a complete awareness of the full functionality of these filler ingredients, which can be fibers, proteins, starch granules and whole grains. But, we show that much can be learned about that from the field of synthetic polymeric foams with (nano)fillers. For edible brittle foams the enhancement of mechanical strength by filler ingredients is less relevant compared to the additional functionalities such as 1) the promotion of bubble nucleation and 2) cell opening-which are much more relevant for the snack texture. The survey of particulate ingredients added to snack formulations shows that they cannot be viewed as inert fillers, because of their strong hygroscopic properties. Hence, these fillers will compete with starch for water, and that will modify the glass transition and boiling point, which are important factors for snack expansion. Filler properties can be modified via extrusion, but it is better if that processing step is decoupled from the subsequent processing steps as mixing and expansion. Several filler ingredients are also added because of their nutritional value, but can have adverse effect on snack expansion. These adverse effects can be reduced if the increase of nutritional value is decoupled from other filler functionality via compartmentalization using micropellets.

A critical review of the growth, drainage and collapse of foams

This review focuses on the current knowledge regarding (i) the mechanisms governing foamability and foam stability, and (ii) models for the foam column kinetics. Although different length scales of foam structure, such as air-water interface and liquid film, have been studied to elucidate the mechanisms that control the foamability and foam stability, many questions remain unanswered. It is due to the collective effects of different mechanisms involved and the complicated structures of foam sub-structures such as foam films, Plateau borders and nodes, and foam networks like soft porous materials. The current knowledge of the effects of solid particles on liquid film stability and foam drainage is also discussed to highlight gaps in our present level of understanding foam systems with solid particles. We also critically review and summarize the models that describe macroscopic foam behaviors, such as equilibrium foam height, foam growth and collapse, within the context of the mechanisms involved.

Counteracting foaming caused by lipids or proteins in biogas reactors using rapeseed oil or oleic acid as antifoaming agents

Foaming is one of the major operational problems in biogas plants, and dealing with foaming incidents is still based on empirical practices. Various types of antifoams are used arbitrarily to combat foaming in biogas plants, but without any scientific support this action can lead to serious deterioration of the methanogenic process. Many commercial antifoams are derivatives of fatty acids or oils. However, it is well known that lipids can induce foaming in manure based biogas plants. This study aimed to elucidate the effect of rapeseed oil and oleic acid on foam reduction and process performance in biogas reactors fed with protein or lipid rich substrates. The results showed that both antifoams efficiently suppressed foaming. Moreover rapeseed oil resulted in stimulation of the biogas production. Finally, it was reckoned that the chemical structure of lipids, and more specifically their carboxylic ends, is responsible for their foam promoting or foam counteracting behaviour. Thus, it was concluded that the fatty acids and oils could suppress foaming, while salt of fatty acids could generate foam.

How antifoams act: a microgravity study

Antifoams are widely used to control or to avoid foam production. In order to work, antifoam particles need to break foam films efficiently, which many antifoams do very well. However, once they have broken a film, to continue to be effective they need to be transported to the next film. We show, for the first time, that buoyancy has an important part in the transport of the antifoam particles. In microgravity, where buoyancy and gravitational drainage are strongly slowed down, diffusion leads to poor antifoam performance. The foam is stable for the duration of the experiment, whereas on Earth the foam starts to disappear immediately. Indeed, microgravity renders highly efficient antifoam practically useless.