Stabilization of nonaqueous foam with lamellar liquid crystal particles in diglycerol monolaurate/olive oil system

Nonaqueous foams stabilized by lamellar liquid crystal (L alpha) dispersion in diglycerol monolaurate (designated as C12G2)/olive oil systems are presented. Foamability and foam stability depending on composition and the effects of added water on the nonaqueous foaming behavior were systematically studied. It was found that the foamability increases with increasing C12G2 concentration from 1 to 3 wt% and then decreases with further increasing concentration, but the foam stability increases continuously with concentration. Depending on compositions, foams are stable for a few minutes to several hours. Foams produced by 10 wt% C12G2/olive oil system are stable for more than 6 h. In the study of effects of added water on the foaming properties of 5 wt% C12G2/olive oil system, it was found that the foamability and foam stability of 5 wt% C12G2/olive oil decreases upon addition of 1 wt% water, but with further increasing water, both the foamability and foam stability increase. Foams with 10% water added system are stable for approximately 4 h. Phase behavior study of the C12G2 in olive oil has shown the dispersion of L alpha particles in the dilute regions at 25 degrees C. Thus, stable foams in the C12G2/olive oil system can be attributed to L alpha particle, which adsorb at the gas-liquid interface as confirmed by surface tension measurements and optical microscopy. Laser diffraction particle size analyzer has shown that the average particle diameter decreases with increasing the C12G2 concentration and, hence, the foams are more stable at higher surfactant concentration. Judging from foaming test, optical micrographs, and particle size, it can be concluded that stable nonaqueous foams in the studied systems are mainly caused by the dispersion of L alpha particles and depending on the particle size the foam stability largely differs.     

Protein foam application for enhanced oil recovery

Protein foam was explored as a foaming agent for enhanced oil recovery application in this study. The influence of salinity and oil presence on bulk stability and foamability of the egg white protein (EWP) foam was investigated. The results were compared with those of the classical surfactant sodium dodecyl sulfate (SDS) foam. The results showed that the EWP foam is more stable than the SDS foam in the presence of oil and different salts. Although, the SDS foam has more foamability than the EWP foam, however, at low to moderate salinities (1–3 wt% NaCl), both foam systems showed improvement in foamability. At a NaCl concentration of 4.0 wt% and above, foamability of the SDS foam started to decrease drastically while the foamability of the EWP foam remained the same. The presence of oil has a destabilizing effect on both foams but the EWP foam was less affected in comparison to the SDS foam. Moreover, increasing the aromatic hydrocarbon compound percentage in the added oil decreased the foamability and stability of the SDS foam more than EWP foams. This study suggests that the protein foam could be used as an alternative foaming agent for enhanced oil recovery application due to its high stability compared to the conventional foams.     

Influence of phosphorylation on the foamability and stability of bovine serum albumin and citrus peel pectin mixed foams

We study the influence of phosphorylation on the foamability and stability of bovine serum albumin (BSA), phosphorylated BSA (pBSA), and citrus peel pectin (CPP) mixed foams as a function of BSA–CPP, pBSA–CPP mixing ratios, at a fixed solution pH of 4.5. Our results show that pBSA solutions result in more stable foams as compared with their BSA counterparts. We further show that the addition of CPP leads to BSA–CPP and pBSA–CPP complexation which increases the foamability and stability of foams as compared with protein-only foams. Also, foam stability is highest for pBSA–CPP mixed foams with mixing ratio pBSA:CPP?=?1:1 due to the combined effect of pBSA–pBSA and pBSA–CPP interactions.     

Investigations on foamability of surface-chemically pure aqueous solutions of functionalized alkylaldonamides

The foamability of the aqueous solutions of functionalized, surface-chemically pure surfactants of the nonionic saccharide-type: N,N-di-n-alkylaldonamides, N-alkyl-N-(2-hydroxyethyl)aldonamides, and N-cycloalkylaldonamides, derivatives of D-glucono-1,5-lactone and/or D-glucoheptono-1,4-lactone, were investigated. The approach of Lunkenheimer and Ma?ysa for the characterization of the foamability and foam stability of these surfactant solutions was applied for these investigations. Using standard parameters related to the different physical stages of the foaming process, foam stability can be described in a simple and easy manner. In general, the investigated alkylaldonamides form foams of medium stability. However, for some homologues a transition from unstable to stable foam systems is observed with increasing concentration. Modifications of the molecular structure of the alkylaldonamides are distinctly reflected in their foam properties. This fact concerns not only changes of the hydrophobic moiety and its functionalization but also slight variations of the saccharide residue. Each homologous series reveals an exceptional foam behavior. In the case of the N,N-di-n-alkylaldonamides the increase of the n-alkyl chain length is accompanied by an increase of the foam stability. The aqueous solutions of the N-alkyl-N-(2-hydroxyethyl)aldonamides reveal most favorable foaming properties for homologues with average alkyl chain lengths. Moreover, it was found that the occurrence of a phase transition in the adsorption layers of the N-cyclooctylgluconamides previously observed by surface tension and surface potential measurements is also remarkably reflected in their foam stability.     

Open-pore biodegradable foams prepared via gas foaming and microparticulate templating

Open-pore biodegradable foams with controlled porous architectures were prepared by combining gas foaming and microparticulate templating. Microparticulate composites of poly(epsilon-caprolactone) (PCL) and micrometric sodium chloride particles (NaCl), in concentrations ranging from 70/30 to 20/80 wt.-% of PCL/NaCl were melt-mixed and gas-foamed using carbon dioxide as physical blowing agent. The effects of microparticle concentration, foaming temperature, and pressure drop rate on foam microstructure were surveyed and related to the viscoelastic properties of the polymer/microparticle composite melt. Results showed that foams with open-pore networks can be obtained and that porosity, pore size, and interconnectivity may be finely modulated by optimizing the processing parameters. Furthermore, the ability to obtain a spatial gradient of porosity embossed within the three-dimensional polymer structure was exploited by using a heterogeneous microparticle filling. Results indicated that by foaming composites with microparticle concentration gradients, it was also possible to control the porosity and pore-size spatial distribution of the open-pore PCL foams.     

Investigation on properties of aqueous foams stabilized by aliphatic alcohols and polypropylene glycol

Foams stabilized by nonionic surfactants are usually moderately stable due to high drainage rate and intense bubble coalescence and coarsening. This study aimed to investigate comparatively the foam properties of aliphatic alcohols (methyl isobutyl carbinol (MIBC) and 2-octanol) and polypropylene glycol (PPG400). Experiments were conducted using the FoamScan method at various surfactant concentrations and gas flow rates where the foam volume, liquid content of foam and foam half-life were determined. The results showed that both foamability and foam stability of surfactant solution increased with increasing gas flow rate and surfactant concentration for all tested surfactants. PPG400 was an unusually strong surfactant having the largest surface activity compared with MIBC and 2-octanol, which exhibited the maximum foaming performance and foam stability at all tested gas flow rates and concentrations. The present study suggested that foam properties depended primarily on the type of surfactant and its concentration and secondarily on the gas flow rate. In addition, properties of interface are closely related to that of foam, which is a significant point if one wants to produce foams for specific applications.     

Wet foams: Formation,properties and mechanism of stability

Overall picture of phenomena occuring during formation and existence of the wet foams is presented. Properties and mechanism of stability are discussed on the example of the wet foams obtained from solutions of two homologous series of surface active substances; the fatty acids and n-alkanols. In general three physical processes which contribute to foam stability can be distinguished: drainage of liquid out of the foam, coalescence and/or rupture of bubbles, and disproportionation (which may be called Ostwald ripening or gas diffusion from one bubble to another). Dynamic and non-equilibrium character of the wet foams is stressed.Motion of a bubble through the solution causes disequilibration of the surface concentration alongside the bubble surface. The surface concentration on the upstream part of the bubble is much smaller than the equilibrium concentration. Thus, the bubbles arrive at the solution surface with non-equilibrium surface concentration, and these actual non-equilibrium surface coverages determine possibility of formation and properties of the foams.Solution content ϕ in the volume of wet foam is high (of an order 307.), while in top foam layer it is much smaller (ϕ≅5%) . It shows that rupture of the wet foam takes place practically only in the top layer of bubbles and durability of these top foam films determine stability and volume of the whole foam column. On the basis of measurements of liquid content ϕ and lifetimes of bubbles in the top foam layer it was estimated that thicknesses of rupture of these top films were of an order of a few micrometers. At such thicknesses the force of disjoining pressure do not attain yet any meaningful value.Influence of kinetics of adsorption, frequency of external disturbances, surface activity of the solute and lifetime of the foam films on magnitude of the surface elasticity forces induced in the systems studied is discussed. It is shown that stability of the wet foams can be explained in terms of the effective elasticity farces, i.e. the surface elasticity forces which are induced at an actual non-equilibrium surface coverage. There is agreement between the courses of the dependences of the foamability parameter (retention time, rt) and the effective elasticity forces as a function of the number n of carbon atoms in the fatty acid and n-alkanol molecule. This shows that the effective elasticity forces are decisive parameter in formation and stability of the wet foams. It also explains why the foamability of a substance with a stronger surface activity can be lower than that of a substance with a weaker surface activity. The foamability, especially under dynamic conditions, cannot simply be correlated with the surface activity.     

应用超临界CO2制备微孔聚丙烯的微孔形貌

研究了应用超临界CO2技术制备微孔聚丙烯时发泡条件和聚丙烯(PP)的熔体强度对微孔形貌的影响。结果表明:在一定的饱和压力下,随着温度的升高,PP的变形能力改善,有利于泡孔的长大。随着饱和压力的增加,PP的熔点降低,升高压力和升高温度具有一定的等同作用。由于CO2在PP内分散的不同,高压低温时得到的泡孔比高温低压时得到的泡孔要规整。降压速率对泡孔形貌的影响因饱和压力的大小而异,饱和压力较高时随着降压速率的提高,孔密度增加,泡孔形貌经历了一个从球体到多面体转变的过程。由于PP熔体强度较低,在发泡温度和PP熔点之间非常接近时,CO2气体容易冲破孔壁而使泡孔呈开孔结构。     

智能水基泡沫研究进展

作为典型的软物质,水基泡沫因具有较小的粒径、较大的比表面积和良好的流动性而广泛应用于洗涤剂、化妆品、食品工程、油气开采等领域。在实际应用中,泡沫的稳定性起着制约性作用。近年来,在环境因素刺激下,能在稳定和非稳定状态之间转变的可控智能泡沫引起了极大关注。针对近年来智能水基泡沫的研究进展,本文综述了基于温度、磁场、光、pH和CO₂响应等智能水基泡沫体系,讨论了不同类型的智能水基泡沫的形成机理及相应性能,展望了智能水基泡沫的应用前景和发展方向。     

The interfacial conformation of polypropylene glycols and foam behaviour

The foam behaviour of low molecular weight polypropylene glycols (PPG) was investigated as a function of concentration and molecular weight (190–2000 g mol⁻¹). For each polypropylene glycol, foam stability increases with concentration and passes through a maximum, beyond which foamability is suppressed as the solubility limit of the glycol is exceeded and droplets of glycol form. Light-scattering data as well as static and dynamic surface tension results provide the key information leading to these interpretations. A maximum in foamability was observed for the PPG molecules with increasing molecular weight (caused by a change in molecular conformation at the interface). This suppresses the Marangoni effect and leads to a decrease in foam stability.     

The influence of the pore size, the foaming temperature and the viscosity of the continuous phase on the properties of foams produced by membrane foaming

Membrane foaming is a new method of foaming. To enlarge the knowledge about the influencing factors and to know how to vary the structure of the resulting foam, different factors were evaluated. A whey protein solution with 10% protein was foamed as a model solution by means of a tubular cross-flow filtration membrane. The pore size of the membrane was varied. The smaller the pore size, the smaller the bubbles produced. As a result, the foam firmness increases and less drainage was observed when smaller pore sizes were applied.

An important factor is that the added amount of gas must be stabilised as completely as possible in the foam. In order to achieve this, both the process and the product parameters were varied. Raising the foaming temperature increased the quantity of stabilised gas. The whey proteins then diffuse faster to the bubble surfaces and stabilise these by unfolding and networking reactions to prevent the coalescence of the bubbles.

The product parameter viscosity was found to influence the foaming result in such a way that up to a viscosity of 40 mPa s the incorporated gas bubbles are stabilised by the higher viscosity. At viscosities higher than 40 mPa s it is difficult to incorporate in the bubbles, and the foam structure becomes coarser due to increased coalescence at the pores of the membrane. The foam stability is enhanced with higher viscosities.     

Foaming in chemical surfactant free aqueous dispersions of anatase (titanium dioxide) particles

Steady-state dynamic aqueous foams were generated from surfactant-free dispersion of aggregated anatase nanoparticles (in the micrometer size range). In order to tune the particle surfaces, to ensure a critical degree of hydrophobicity (so that they disperse in water and generate foam), the particles were subjected to low-temperature plasma treatment in the presence of a vapor-phase silane coupling agents. From ESCA it was shown that hydrophobization only occurred at a small number of surface sites. Foamability (foam generation) experiments were carried out under well-defined conditions at a range of gas flow rates using the Bikermann Foaming Column.1 The volume of the steady-state foams was determined under constant gas flow conditions, but on removing the gas flow, transient foams with short decay times (<5 s) were observed. The foamability of the steady-state foams was found to be dependent on (a) the time of plasma treatment of the particles (surface hydrophobicity), (b) the particle concentration in the suspension, and (c) the state of dispersion of the particles. High foamability was promoted in the neutral pH regions where the charged particles were highly dispersed. In the low and high pH regions where the particles were coagulated, the foamability was considerably reduced. This behavior was explained by the fact that the large coagula were less easily captured by the bubbles and more easily detached from the interface (during the turbulent foaming conditions) than individual dispersed particles.     

The effect of silica nanoparticles on the stability of aqueous foams

An experimental study was performed on aqueous foams stabilized by a mixture of hexadecyltrimethylammonium bromide (HTAB) and negatively-charged silica nanoparticles. The effects of the nanoparticles on the stability of foams at different HTAB concentrations were investigated. The foams were characterized by measuring their foamability and stability. Rheological behavior of the foams was also studied. Furthermore, rheology of the air–water interfaces was studied in the linear and nonlinear deformation ranges. The thickness of the monolayer at the interface was measured. The actual size of the silica nanoparticles at the air–water interface was measured by transmission electron microscopy. Based on these measurements, the interaction between the monolayers across the foam film containing HTAB and nanoparticles was investigated. Smaller silica nanoparticles (i.e. diameter less than 10?nm) adsorbed at the air–water interface whereas the larger particles remained in the sub-phase or in the bulk liquid phase. It was found that these nanoparticles strongly influenced the foaming behavior at the low HTAB concentrations (i.e. below the CMC). A Langmuir-type monolayer was formed. The presence of the nanoparticles at the air–water interface provided mechanical strength to the foam films and prevented their rupture. This hindered coalescence of the bubbles, which resulted in a stable foam.     

Comparative Analysis of the Properties of Tween‐20, Tween‐60, Tween‐80, Arlacel‐60, and Arlacel‐80

Foamability and foam stability, emulsifying power, surface tension, and interfacial tension were investigated for Tween‐20 (polyoxyethylene sorbitan monolaurate), Tween‐60 (polyoxyethylene sorbitan monostearate), Tween‐80 (polyoxyethylene sorbitan monooleate), Arlacel‐60 (Sorbitan stearate), and Arlacel‐80 (Sorbitan oleate). Among all the surfactants tested for their foaming power and foamabilty, Arlacel‐60 and Arlacel‐80 showed the best results; the foaming power and foamability was found to be 100%. The surfactants having foam stability more than 50% can be considered as metastable and those less than 50% are considered as low‐stability foams. In case of surface tension and interfacial tension property measurements, Arlacel‐80 showed the best results. At 1% surfactant concentration, the surface tension and interfacial tension of Arlacel‐80 was found to be 29.9 dynes/cm and 1.1 dynes/cm at 30°C ambient temperature. Also, Arlacel‐60 was found to exhibit the best emulsifying power among all the surfactants tested. At 30°C, the emulsifying property of Arlacel‐60 was 6 hours.     

Generation of discharges in dynamic foam for oxidants formation using various types of electrodes

An innovatory apparatus for the discharge generation in foaming conditions was constructed. The main goal of the research was to obtain various kinds of oxidants, useful in Advanced Oxidation Processes (AOP) in one compact reactor, potentially even in the treated medium. Such an application of dynamic foam, created without the addition of surfactant has not been investigated as yet. To find the optimum conditions for the efficient foam generation and the discharge development and moreover, to assure the presence of oxidants in sufficient concentrations several electrode materials and electrode set-ups were tested. The experiments were done in the metal plate-to-metal plate, metal plate-to-dielectric plate, needles-to-metal plate and needles-to-dielectric plate electrodes’ set-ups. The discharge gap space ranged from 4 mm in the case of plate-to-plate electrodes to 7 mm in the case of needles-to-plate electrodes. Generally, the highest oxidants’ concentrations at the highest comparable gas flow rate were obtained in the needles-to-dielectric plate arrangement, where 521 and 875 ppm of gaseous ozone, 0.36 and 0.5 mg dm⁻³ of dissolved ozone and 59 and 62 mg dm⁻³ of hydrogen peroxide were obtained at 14 kV of applied voltage and at 5 dm³ min⁻¹ of the substrate gas flow in air and oxygen, respectively. The presence of OH radicals was confirmed by the spectroscopic measurements. The larger gap size was more advantageous from the foam formation point of view and the dielectric layer assured more uniform spatial discharge development between the electrodes.     

Enhancing foam stability in porous media by applying nanoparticles

Several new foaming agent formulations (surfactants and polymers) in the presence of multi-walled carbon nanotube (MWCNT) were developed in 3% salinity (NaCl, 2.4?wt%, CaCl₂, 0.6?wt%). The dispersion stability of the MWCNT and the viscosity of the solutions were examined as a prerequisite for reservoir applications. Foam was generated in situ and one-dimensional flow-through tests were performed by co-injecting air and foaming solution either in the presence of MWCNT or at particle-free condition. The pressure drop (Δp) across the sand-pack and the nanoparticles breakthrough were closely monitored. The fluid injection rate, gas fraction, and the effect of MWCNT on foams in porous media were investigated.

Our results reveal that foams stabilized by the selected nanoparticles are capable of generating stronger foams leading to higher apparent Δp. The Δp profile varies with gas fraction, which largely affects the foam texture and quality. Also, the viscosity of foaming agent solutions influences Δp values. Adding MWCNT to the foaming agent solutions appears beneficial to the flooding as surfactants adsorption onto nanoparticle surfaces, which facilitates surfactants partitioning to the G/L interface.

Addition of nanoparticles in the developed foam formulations leads to the formation of high-quality stronger foams in porous media, which could potentially improve the sweep efficiency and increase the oil recovery.     

Increased expansion ratio,cell density,and compression strength of microcellular poly(lactic acid) foams via lignin graft poly(lactic acid) as a biobased nucleating agent

Green and renewable foaming poly(lactic acid) (PLA) represents one of the promising developments in PLA materials. This study is the first to use the lignin graft PLA copolymer (LG‐g‐PLA) to improve the foamability of PLA as a biobased nucleating agent. This agent was synthesized via ring‐opening polymerization of lignin and lactide. The effects of LG‐g‐PLA on cell nucleation induced by the crystallization, rheological behavior, and foamability of PLA were evaluated. Results indicated that LG‐g‐PLA can improve the crystallization rate and crystallinity of PLA, and play a significant nucleation role in the microcellular foam processing of PLA. LG‐g‐PLA improved the foam morphology of PLA, obtaining a reduced and uniform cell size as well as increased expansion ratio and cell density. With the addition of 3 wt% LG‐g‐PLA content, the PLA/LG‐g‐PLA foams increased the compressive strength 1.6 times than that of neat PLA foams. The improved foaming properties of PLA via a biobased nucleating agent show potential for the production and application of green biodegradable foams.     

Glass foam from window panes and bottle glass wastes

Glass foams are building materials that now compete with classic insulating polymeric and fiber materials for thermal enveloping. The low flammability, high chemical durability and thermal stability are distinct advantages over polymeric materials. The present paper proposes the possibility of producing glass foam using two types of recycled glass wastes (window panes and bottle glass) together with plaster wastes from used ceramic casting molds as foaming agent. Optical microscopy, measurements of apparent porosity and density, hydrolytic and chemical stability, as well as thermal conductivity were used in order to characterize the obtained glass foams as insulator materials for the building industry. The apparent porosity of glass foams ranges between 20.19–54.54% when using window glass wastes, and 18.77–51.75% with bottle glass wastes. Thermal conductivity was less than 0.25 W mK-1 for all the studied glasses. The obtained results confirm that there exists an alternative method for producing glass foams, for example, from glass wastes and used ceramic plaster molds, which are utilized as foaming agents with good chemical stability and insulating properties.     

Prediction of the Properties of a Binary Surfactant Mixture of Arlacel‐165 and Myrj‐59 in Aqueous System

Foamability and foam stability, emulsifying power, surface tension, and interfacial tension were investigated for different ratios of binary surfactant system of Arlacel‐165 (glyceryl stearate (and) PEG‐100 stearate) and Myrj‐59 (polyoxyethylene 100 stearate). Among all the ratios tested for their foaming power and foamabilty, the ratios 8:2, 5:5, 4:6, 2:8, and 1:9 of Arlacel‐165 and Myrj‐59 showed the best results. At these ratios, the foaming power and foamability was found to be 100%. The surfactants having foam stability more than 50% can be considered as metastable and those less than 50% are considered as low‐stability foams. In case of surface tension and interfacial tension property measurements, 8:2 and 9:1 showed the best results. At 8:2 and 9:1 of Arlacel‐165 and Myrj‐59, the surface tension was found to be 37.7 dynes/cm and 1.33 dynes/cm respectively at 30°C ambient temperature. Also, 7:3 of this binary mixture was found to exhibit the best emulsifying power among all the ratios tested. At 30°C, the emulsifying property of the binary mixture was 6 hours.     

Intrinsic styrene/maleic anhydride copolymer foam; a new green foaming technology

DSM has developed a new foaming technology based on carbon dioxide released via a controlled chemical reaction through catalyzed decarboxylation of SMA, a copolymer of Styrene (S) and maleic anhydride (MA). This carbon dioxide is thus used as an environmentally friendly blowing agent to generate intrinsically foamed SMA-based materials. The modulus of the foam exceeds by far (factor of 2–3) the modulus of common thermoplastic foams based on e.g. PS. The tensile strength is also higher (10%). This opens up many opportunities for SMA foams in structural applications. One example is roofliners. SMA has also been successfully applied as a chemical blowing agent (e.g. in combination with ABS) for the production of a high-density foam on an injection moulding machine or an extruder. In this paper the chemical background, processing, properties and some applications of intrinsically foamed SMA will be discussed.