Stability Of Wet Foams Research Articles

Chemistry and Physics of Wet Foam Stability for Porous Ceramics: A Review

The unique structural properties of porous ceramics, such as low thermal conductivity, high surface area, controlled permeability, and low density, make this material valuable for a wide range of applications. Its uses include insulation, catalyst carriers, filters, bio-scaffolds for tissue engineering, and composite manufacturing. However, existing processing methods for porous ceramics, namely replica techniques and sacrificial templates, are complex, release harmful gases, have limited microstructure control, and are expensive. In contrast, the direct foaming method offers a simple and cost-effective approach. By modifying the surface chemistry of ceramic particles in a colloidal suspension, the hydrophilic particles are transformed into hydrophobic ones using surfactants. This method produces porous ceramics with interconnected pores, creating a hierarchical structure that is suitable for applications like nano-filters. This review emphasizes the importance of interconnected porosity in developing advanced ceramic materials with tailored properties for various applications. Interconnected pores play a vital role in facilitating mass transport, improving mechanical properties, and enabling fluid or gas infiltration. This level of porosity control allows for the customization of ceramic materials for specific purposes, including filtration, catalysis, energy storage, and biomaterials.

Pickering emulsion stabilized by cellulose nanofibril from pineapple leaves for biofoam manufacture

Cellulose nano fibril (CNF) can be selected as an agent of pickering emulsion in biofoam manufacture. This study thoroughly investigates the pickering emulsion method for producing biofoam, the characterization of CNF from pineapple leaves, the production of biofoam with various concentration of CNF and surfactant, and the effect of these parameters on the properties of wet foam and dry foam. CNF was created by mechanical grinding then the stability and morphology were evaluated. The pickering emulsion mechanism in biofoam manufacture was investigated using foamability and foam stability with various CNF and surfactant concentration. As the results, CNF concentrations will create varying zeta potential values. The morphology of CNF shows that it has a structure-like entangled network. The stability test demonstrates that adding CNF improves the stability and foamability of biofoam by the pickering effect. Biofoam without CNF has an unstable structure and is easily collapse when dried in an oven. The concentration of CNF and the amount of surfactant utilized altered the qualities of both wet and dry foam. The lower concentration of CNF and the addition of surfactant could increases foamability, high porosity, water absorption, and biodegradability; as well as low density, contact angle and bending characteristics. In biofoam that consists of 2 % CNF, the stability of wet foam increases as the amount of surfactant added, resulting in a biofoam with low tensile strength.

Exploring Foam Drainage in Fiber-Foam: A Review

The foam drainage is extremely important in many situations where fiber foams are used. Enhancing wet foam stability requires a complete understanding of the mechanisms and factors affecting wet foam drainage. Investigation of the drainage behavior of fiber foams has been studied in this review. The mechanics behind fiber foam drainage are discussed in detail, along with the influence of surfactant concentration, fiber consistency, and other variables. It also investigated adding additives, such as chemi-thermo-mechanical pulp (CTMP), affects foam drainage. Highlighting the most recent developments in experimental and theoretical methods for describing and forecasting foam drainage behavior are presented. This review acts as a reference to offer useful understanding of the essential factors of foam drainage in fiber foams solution.

High-strength porous alumina ceramics prepared from stable wet foams

Porous ceramics have been widely used in heat insulation, filtration, and as a catalyst carrier. Ceramics with high porosity and high strength are desired; however, this high porosity commonly results in low strength materials. In this study, porous alumina with high porosity and high strength was prepared by a popular direct foaming method based on particle-stabilized wet foam that used ammonium polyacrylate (PAA) and dodecyl trimethyl ammonium chloride (DTAC) as the dispersant and hydrophobic modifier, respectively. The effects of the dispersant and surfactant contents on the rheological properties of alumina slurries, stability of wet foams, and microstructure and mechanical properties of sintered ceramics were investigated. The microstructure of porous ceramics was regulated using wet foams to achieve high strength. For a given PAA content, the wet foams exhibited increasing stability with increasing DTAC content. The most stable wet foam was successfully obtained with 0.40 wt% PAA and 0.02 wt% DTAC. The corresponding porous alumina ceramics had a porosity of 82%, an average grain size of 0.7 µm, and a compressive strength of 39 MPa. However, for a given DTAC content, the wet foams had decreasing stability with increasing PAA content. A possible mechanism to explain these results is analyzed.

Influence of wet foam stability on the microstructure of ceramic shell foams

In this study, recycled ceramic shell particles from the mold used in precision casting, which consists of coating a wax model with several layers (shell) of mullite and zirconia particles of different sizes, were used as raw material to prepare stable wet-foams by direct foaming and gelcasting using ovalbumin. The control of suspension parameters, such as pH, dispersant concentration, solids concentration and stirring velocity, can influence the foam stability against destabilization mechanisms (such as drainage, coalescence, and Ostwald ripening), optimizing the final properties of the cellular ceramic structures. The rheological behavior of suspensions and the gel point temperature of foams was also evaluated. The evolution of the bubbles-sizes (as a function of time) into the wet foam structure was analyzed by Axio Vision LE and ImageJ software. The fired ceramic shell foam (1550 ​°C, 2 ​°C/min, for 2 ​h) exhibited porosities higher than 80%, characterized by a highly interconnected network of spherical pores, with sizes ranging from 518 ​± ​29 to 1088 ​± ​103 ​μm and compressive strength of 0.9 ​± ​0.2 ​MPa. The morphological features and mechanical strength of the obtained foam indicating the possibility that it could be employed as low-cost replacement for radiant porous burners applications.

Effects of flow constriction on foamed viscous shear-thinning fluids downstream of a continuous multi rotor-stator foaming device

Foam flow through processing equipment can seriously affect the structure of the foam and its quality attributes. In the design of a foam formulation and its flow system, it is therefore important to consider the possible implications on the end-of-pipe structure of the foam to ensure preservation of product quality. We study the flow through a straight pipe with and without the presence of a narrow orifice plate and, hence, the dynamic stability of wet food relevant foams of fine texture and high static stability generated from complex formulations of viscous shear-thinning fluids in a continuous multi rotor-stator device. The effects of fluid formulation, gas-liquid ratio, rotor speed and constriction aperture size are investigated. Constricted foam flow can cause important transformations in the foam due to significant bubble coalescence and loss of air volume resulting in much coarser and much less stable foam. Increased surfactant content, liquid viscosity and rotor speed reduce bubble coalescence and help preserve foam structure. • A continuous multi rotor-stator device generates foam of fine and stable structure. • Foam flow through a constriction causes bubble coalescence and loss of air volume. • Constricted foam flow leads to coarser unstable foam. • The higher the local pressure drop the more severe the foam damage incurred. • Increased surfactant content, liquid viscosity and rotor speed help preserve foam.

Wet Foam Stability from Colloidal Suspension to Porous Ceramics: A Review

Wet Foam Stability from Colloidal Suspension to Porous Ceramics: A Review

The high porosity silicon nitride foams prepared by the direct foaming method

Silicon nitride foams with porosity higher than 90% were fabricated by direct foaming method. The influence of the surfactant content, solid content and rotating speed on the foamability and stability of wet foams were discussed and the corresponding effect on the total porosity, pore size distribution and mechanical property of ceramic foams were systematically investigated. The results showed that the pore structure and porosity, the compressive strength of Si3N4 ceramic foams could be controlled by tailoring surfactant and solid content. The results indicated that rotating speed had a great impact on the pore size distribution. Si3N4 ceramic foams with porosity of 90.8–96.4% and compressive strength of 0.37–5.53 MPa were obtained.

Chitin Nanofibrils to Stabilize Long-Life Pickering Foams and Their Application for Lightweight Porous Materials

The demand of sustainable development is challenging researchers to convert renewable resourced biomass into functional materials via environmentally friendly and sustainable pathways. This work introduces a long-life Pickering foam stabilized by chitin nanofibers (CNFs) as colloidal rod-like particles, and a facile method for fabricating lightweight porous solid foams that recycles biomass materials derived from seafood waste. These foams were formed by combining nonionic surfactant Tween 20 (T20) and CNFs, with the CNFs being irreversibly adsorbed at the air–water interface to provide Pickering stabilization. At a concentration of 7.5 mg/mL, the foams could be stable for over 1 week without any apparent drainage. The rheological data indicated the formation of gel networks by self-aggregated CNFs at the air–water interface, which provided long-term stabilization by preventing foam coalescence and disproportionation. This long-term stability of CNF-T20 wet foam has permitted the fabrication of solid poro...

Highly porous barium strontium titanate (BST) ceramic foams with low dielectric constant from particle‐stabilized foams

AbstractA novel method for fabrication of highly porous barium strontium titanate (BST) ceramic foams based on particle‐stabilized foaming method was developed for the first time, in which propyl gallate (PG) was employed as BST particle modifier. The results showed that the stability of wet BST foams closely depends on the pH value and PG concentration, which could be explained by the adsorption behavior of PG on BST particle surface. BST ceramic foams with dense, uniform, and closed pore and defect‐free wall were obtained. The pore size and porosity can be well controlled by adjusting solid loading and sintering temperature. It was revealed that not only sintering temperature but also solid loading significantly influenced the growth of BST grain. The BST ceramic foams exhibited high porosity in the range of 81%‐95%, low dielectric constant in the range of 47‐150, and low dielectric loss below 0.0025. The BST ceramic foams with higher porosity presented a tendency of lower dielectric constant and the fitting results indicated that the natural logarithm of dielectric constant was linear correlated with porosity.

The effect of wet foam stability on the microstructure and strength of porous ceramics

Wet foam stability is of prime importance in fabricating porous ceramics with the desired microstructure and mechanical properties. In this research, wet foams were fabricated via direct foaming after separately adding an anionic surfactant (TLS) and a cationic surfactant (DTAC) into alumina slurries with a copolymer of isobutylene and maleic anhydride (PIBM) as both the dispersant and the gelling agent. The foam stability was evaluated by a stability analyzer. The bubble size rapidly increased in the wet foam with TLS as the foam stabilizer and many large bubbles appeared within 60min. The wet foam containing DTAC was very stable. Cationic DTAC increased the hydrophobicity of alumina particles by interacting with the anionic PIBM adsorbed on the particles. The hydrophobically modified particles acted as the foam stabilizer and enhanced the wet foam stability. Furthermore, the fast gelling speed of the slurry containing DTAC also enhanced the wet foam stability. The average cell size of the ceramic with 82.9% porosity from the wet foam with TLS was 188µm and the compressive strength was 9.7MPa. The counterparts from the wet foam with DTAC were 54µm of average cell size and 18.1MPa of compressive strength. The superior stability of wet foam brought about a smaller cell size and higher strength of the resultant ceramic.

Strength enhancement of ultralight alumina‐dried foams from particle‐stabilized foams with assistance of agar and PVA

AbstractThe weak compressive strength of dried ceramic foams is a disadvantage of fabricating ultralight ceramic foams, especially for the ceramic foams with porosity exceeding 95%. In this study, dried alumina foams were enhanced by agar and PVA‐freezing‐thawing using sodium dodecyl sulfate as surfactant. It is found that the two additives have no negative influence on adsorption of sodium dodecyl sulfate on alumina particles as well as the hydrophobic character of alumina particles. Stable alumina particle‐stabilized foams were prepared with less than 0.5 wt% agar and 1.0 wt% PVA. High additive concentration above the critical values weakens stability of wet foams, which is probably due to the aggregate of alumina particles caused by long‐chain molecules connecting. The compressive strength of dried alumina foams has a significant improvement with the employment of agar and PVA‐freezing‐thawing. The dried foams prepared with 1wt% PVA assisted by freezing‐thawing has porosity of 97.1% and compressive strength of 0.16 MPa, which could maintain integrity of dried foams without destruction in the fabricating process.

Highly porous SiC ceramics from particle-stabilized suspension

This study reports on the wet-foam stability of porous ceramics that are formed from a particle-stabilized colloidal suspension for which the direct-foaming method is used. To stabilize the wet foam, an initial colloidal suspension of silicon carbide (SiC) was partially hydrophobized by the surfactant octylamine (12.5 wt.%). The influence of the binder content on the wet-foam stability in terms of the air content, bubble size, contact angle, surface tension, surface-free energy, Laplace pressure, and relative bubble size is described in this paper. The results show a wet-foam stability of more than 95% that corresponds to an air content of 87.8%, an increase of the adsorption free energy from 3.0 × 10−5 to nearly 7.5 × 10−5 J, a Laplace pressure increase from 0.16 to 0.20 mPa, and a relative bubble size of 1.3 for the colloidal particles with a 20 wt% binder content. The uniform distribution of the highly open/interconnected pores could be controlled with thick struts and an increasing of the binder content up to 20 wt%, leading to the achievement of a higher-stability wet foam with respect to the porous ceramic.

Solid nanofoams based on cellulose nanofibers and indomethacin—the effect of processing parameters and drug content on material structure

The unique colloidal properties of cellulose nanofibers (CNF), makes CNF a very interesting new excipient in pharmaceutical formulations, as CNF in combination with some poorly-soluble drugs can create nanofoams with closed cells. Previous nanofoams, created with the model drug indomethacin, demonstrated a prolonged release compared to films, owing to the tortuous diffusion path that the drug needs to take around the intact air-bubbles. However, the nanofoam was only obtained at a relatively low drug content of 21wt% using fixed processing parameters. Herein, the effect of indomethacin content and processing parameters on the foaming properties was analysed. Results demonstrate that a certain amount of dissolved drug is needed to stabilize air-bubbles. At the same time, larger fractions of dissolved drug promote coarsening/collapse of the wet foam. The pendant drop/bubble profile tensiometry was used to verify the wet-foam stability at different pHs. The pH influenced the amount of solubilized drug and the processing-window was very narrow at high drug loadings. The results were compared to real foaming-experiments and solid state analysis of the final cellular solids. The parameters were assembled into a processing chart, highlighting the importance of the right combination of processing parameters (pH and time-point of pH adjustment) in order to successfully prepare cellular solid materials with up to 46 wt% drug loading.

Highly-closed/-Open Porous Ceramics with Micro-Beads by Direct Foaming

This study reports on wet-foam stability with respect to porous ceramics from a particle-stabilized colloidal suspension that is achieved through the addition of polymethyl methacrylate (PMMA) using a wet process. To stabilize the wet foam, an initial colloidal suspension of Al₂O₃ was partially hydrophobized by the surfactant propyl gallate (2 wt.%) and SiO₂ was added as a stabilizer. The influence of the PMMA content on the bubble size, pore size, and pore distribution in terms of the contact angle, surface tension, adsorption free energy, and Laplace pressure are described in this paper. The results show a wet-foam stability of more than 83%, which corresponds to a particle free energy of 2.7 × 10 −12 J and a pressure difference of 61.1 mPa for colloidal particles with 20 wt.% of PMMA beads. It was possible to control the uniform distribution of the open/closed pores by increasing the PMMA content and by adding thick struts, leading to the achievement of a higher-stability wet foam for use in porous ceramics.

ZrTiO4 porous ceramics fabricated from particle-stabilized wet foam by direct foaming

Indent ZrTiO4 ceramics are widely used to manufacture electrical and optical devices. This study reveals an approach for the production of micro-porous ceramics consisting of TiO2 and ZrO2 by using a direct foaming method. ZrO2 particles in a colloidal suspension were partially hydrophobized by using propyl gallate as an amphiphile in a suitable pH range. Different mole ratios of the TiO2 suspension were added to the surface-modified ZrO2 suspension. The contact angle was found to be around 54° and the adsorption free energy to be 1.68 × 10−11 ∼ 9.2 × 10−12 J·A Laplace pressure of about 2.0 ∼ 2.2 mPa, corresponding to a wet foam stability of about 80 ∼ 85% was determined. A microstructure analysis was done after the dried samples had been sintered to obtain porous ceramics.

Particle Stabilized Wet Foam to Prepare SiO<sub>2</sub>-SiC Porous Ceramics by Colloidal Processing

Porous ceramics with tailored pore size and shape are promising materials for the realization of a number of functional and structural properties. A novel method has been reported for the investigation of the role of SiC in the formation of SiO₂ foams by colloidal wet processing. Within a suitable pH range of 9.9 ~ 10.5 SiO₂, particles were partially hydrophobized using hexylamine as an amphiphile. Different mole ratios of the SiC solution were added to the surface modified SiO₂ suspension. The contact angle was found to be around 73°, with an adsorption free energy 6.8 × 10 −12 J. The Laplace pressure of about 1.25 ~ 1.6 mPa was found to correspond to a wet foam stability of about 80 ~ 85%. The mechanical and thermal properties were analyzed for the sintered ceramics, with the highest compressive load observed at the mole ratio of 1:1.75. Hertzian indentations are used to evaluate the damage behavior under constrained loading conditions of SiO₂–SiC porous ceramics.

Interfacial and foaming characterisation of mixed protein-starch particle systems for food-foam applications

This work presents mixed protein-starch systems as effective foaming agents and stabilisers. The starch size and hydrophobicity play a dominant role in determining the levels of synergy observed. Egg White Protein (EWP) and Pea Protein Isolate (PPI) were selected at two concentrations (0.5, 1 wt. %) along with three starch species of concentrations between 0.5, 1, 3 & 5wt. %. Two commercial OSA-modified starches are compared to a native granule and its heat-treated counter part. The system's effectiveness to incorporate air (overrun) as well as its capacity to hold structure (half life) is evaluated. starch's physical properties (contact angle and size) and their effect on the nature of the Air/Water (A/W) interface (interfacial dilatation rheology, surface tension) are also explored. The effect of protein species as well as starch size and hydrophobicity on foam stability is determined and discussed. The study demonstrates that addition of OSA modified starch (0–5wt%) to (EWP) foams can enhance foam stability by up to 1200% without compromising the foaming capacity, mainly due to a hypothesised exclusion volume effect. Where as the larger heat-treated starch granule is found to increase stability of wet foams by 800%, through a combination of mechanisms.

Wet foam stability and tailoring microstructure of porous ceramics using polymer beads

The microstructures of the porous ceramics are improved considerably using polymethyl methacrylate (PMMA) as a pore template since particles tend to adsorb irreversibly at the air-water interface. This paper presents a versatile approach for the production of porous SiO2 ceramics by a process of direct foaming with the addition of PMMA beads. The adsorption free energy of the colloidal suspension was found to be 2.0 × 109 kT. A wet foam stability of >80% was achieved using the surfactant hexylamine (0.05 M), which resulted in a colloidal suspension with the highest surface tension (116.2 mN m− 1).

Effect of amphiphile chain length on wet foam stability of porous ceramics

Inorganic oxide particles such as Al2O3 are partially hydrophobized using carboxylic acids of different chain length to produce wet foams exhibiting high air contents and remarkable stability. Stabilization of wet foam is achieved by in-situ hydrophobization which is very important to avoid the instability that occurs due to large interfacial area of the gas liquid interface. The concentration of amphiphilic molecules in the initial suspension and the chain length of their hydrophobic tail are modified to tailor the degree of surface hydrophobicity of the Al2O3 particles. Hydrophobization of Al2O3 surface is achieved through the adsorption of carboxylic acid exhibiting a functional hydroxyl group that efficiently anchors on the particle surface and a short hydrophobic tail remains in contact with the aqueous phase. The wet foam features adsorption free energy of 2.05×10–13J to 8.22×10–13J and Laplace pressure of 0.60 to 1.64mPa which indicate good wet foam stability of about 80–90%.