Single Foam Research Articles

The traveling foam wavefront in fractured porous medium

This paper investigates the foam injection in a fractured porous medium modeled as a thin layer surrounded by the other two. We show the formation of the single foam front using the traveling wave solution, which is characterized geometrically as a wave that moves with a constant velocity, maintaining its profile over time.To allow this analysis, we derive a formula describing the foam front velocity in n-layered porous medium extending previously known results for two layers. All the theoretical analysis was validated through the computation simulations of the realistic model using parameter data from laboratory experiments.

Philaenus tesselatus (Hemiptera: Aphrophoridae), the main potential vector of Xylella fastidiosa in Morocco: seasonal abundance, phenology and host-plant colonization by nymphs

Summary The bacterium Xylella fastidiosa presents a potential risk to the Moroccan flora, particularly for the citrus, olive, almond and grapevine industries. Philaenus tesselatus, the meadow spittlebug, is the most important Moroccan spittlebug, though recorded with uneven occurrence and considered to be the main potential insect vector of X. fastidiosa. A three-year field survey (2019 to 2021) was conducted at three sites in the provinces of Larache and Kenitra in northwestern Morocco, to study seasonal abundance, phenology and host-plant colonization by nymphs. Philaenus tesselatus is a univoltine species. Nymphs occurred in groundcover from end of mid-March to mid-May, with abundance peaking between end of March and mid-May. Emergence of teneral adults occurred between April and May, depending on the year. Adults were present on ground vegetation from March until early August, with the highest abundances surveyed by sweep net in April, and occurred in canopy in low abundance between the end of May and mid-September, depending on site. Both nymphal and adult abundances were significantly higher in Larache than at the other two sites. Philaenus tesselatus, the meadow spittlebug, is a polyphagous species, recorded on nine botanical families of host plant species including Asteraceae, Poaceae, Fabaceae, Polygonaceae, Apiaceae, Primulaceae, Urticaceae, Papaveraceae and Malvaceae, and 37 host plant species, of which 29 were identified. The Asteraceae were best represented. Carduus pycnocephalus, Vulpia geniculata, Anthoxanthum odoratum and Cistus salviifolius were the most suitable for this spittlebug. Avena barbata, L. foemina, Scolymus hispanicus and S. oleraceus were dominant in the herbaceous layer. Philaenus tesselatus preferred to feed on the mid-section of the host plants. A single foam can host zero to five individuals, but foams with one or two nymphs were most frequent. Implications of our findings for the setting up of a survey program to control X. fastidiosa and its vectors in case the bacterium is introduced to Morocco are discussed.

Balance Error Scoring System in the assessment of chronic ankle stability: A systematic review and meta-analysis.

Chronic ankle instability (CAI) is a common musculoskeletal injury associated with static balance deficits. The Balance Error Scoring System (BESS) is commonly used to assess static balance in individuals with CAI. However, the sensitivity of BESS in detecting balance deficits in CAI is unknown. This study compared BESS performance between people with CAI and controls and investigated which stances most effectively identified balance deficits in individuals with CAI. Seven electronic databases (Web of Science, CINAHL, Embase, PubMed, Scopus, SPORTDiscus, and Cochrane Library) were searched from July 13, 2023, to September 10, 2023, using the ankle instability and balance related terms as keywords to search original studies and perform a systematic review. Studies that compared BESS scores between individuals with CAI and healthy controls were systematically identified. Extracted data included study characteristics, participant demographics, and assessment details. The risk of bias was assessed using the Newcastle-Ottawa Scale. The standardized mean difference (SMD) and 95% confidence interval (CI) were used as effect sizes to compare groups for the BESS components used to assess CAI. Six studies met the eligibility criteria. The double-leg foam stance yielded an SMD of -0.02 (95% CI: -0.32 to 0.29), with an I2 value of 3.5%. Significant differences between groups were noted in the single foam (SMD = 0.89; 95% CI: 0.33-1.45; I2 = 78.3%) and single firm (SMD = 0.62; 95% CI: 0.14-1.10; I2 = 72.1%) performances, although both demonstrated high heterogeneity. Conversely, the tandem foam (SMD = 0.77; 95% CI: 0.51-1.02; I2 = 0.0%) and tandem firm (SMD = 0.38; 95% CI: 0.11-0.68; I2 = 23.8%) performances showed small to moderate between-group differences with considerably lower heterogeneity. This review indicates that tandem stances on foam and firm surfaces in the BESS are reliable indicators of static balance deficits in individuals with CAI.

Influence of the foam-fin structure on the thermal performance of a coupled phase change liquid cooling module

Effective thermal management is key to ensuring the reliable operation of high power electronic equipment. In this study, the strategy of phase transition and liquid cooling coupling applied to transient high power electronic equipment has been examined. In order to improve the performance of the phase changing material (PCM) in temperature control, the effects of the coupling structure have been addressed with a consideration of fin, copper foam (CF), graphite foam (GF), fin-copper foam (FCF) and fin-graphite foam (FGF) structures in heat dissipation. In this study, pure paraffin wax (PPW) was used as phase change material to prepare heat sinks based on the above five structures. The experimental study investigates the impact of different thermal conductivity strategies on temperature control characteristics, with a focus on cold capacity recovery and the combined phase change and liquid cooling, using pure paraffin wax module as a reference. The results have revealed that the fin-foam coupling structure delivers a better PCM performance than the single fin or foam structure. Operating at a heating power of 10 W, 15 W and 20 W, the temperature control time of the FGF structure was increased by 13.6 %∼14.6 % relative to the GF structure. At 15 °C with flow rates of 1 L/min, 1.5 L/min, 2 L/min liquid cooling conditions, the cooling capacity recovery time was reduced by 18.8 %, 17.2 %, 19.7 %, respectively. In the phase-change liquid-cooling coupling temperature control experiment, the final temperature increase in the FGF system was 11.7 °C -15.2 °C lower than that of the GF system under the same water temperature and volume flow for a 50 W heat source. The incorporation of fins also enhanced the thermal conductivity strengthening capability of the copper foam and reduced the cold recovery time. Based on the comprehensive evaluation, the FGF structure demonstrates superior temperature control performance and cold recovery characteristics of PCM, making it an optimal strengthening method. Following closely are the FCF, GF, Fin and CF structures. Compared to pure paraffin modules, these five modules exhibit varying degrees of improvement in temperature control and cold capacity recovery efficiency. This study provides guidance for optimizing heat sink design based on PCM in electronic applications.

Relation between Tensile Strut and Compressive Foam Deformation Behaviour: Failure Mechanisms and the Influence of Dendritic Versus Globular Grain Structure in an AlSi7Mg0.3 (A356) Precision‐Cast Open‐Cell Foam

Open‐cell aluminum foams are gaining importance for the design of lightweight structures and as electrodes in lithium‐ion batteries. AlSi7Mg0.3 foams were produced by a modified investment‐casting process. By tuning the mold temperature, a change from the usual nearly monocrystalline dendritic to a polycrystalline globular grain structure was achieved. Tension and compression tests on single struts and foam specimens, respectively, were combined with digital image correlation, scanning electron microscopy, and phase‐contrast enhanced micro‐computed tomography in a synchrotron facility to correlate the mechanical properties and the failure mechanisms with the microstructure. The “globular” foams exhibited a lower strength and a less pronounced subsequent stress drop than the “dendritic” foams, and the deformation mechanism changed from shear‐band dominated failure to a layer‐by‐layer collapse, because of the lower strength and higher ductility of the “globular” struts. The “dendritic” struts have a more homogeneous microstructure, while the “globular” struts often contain silicon agglomerates in their central region. Accordingly, the latter struts exhibit a higher degree of scatter for the fracture strain. Thus, the arrangement of the silicon particles and the eutectic determines the mechanical properties on the strut level and thereby the failure behavior on the foam level.This article is protected by copyright. All rights reserved.

A Single Component, Single Layer Flexile Foam Evaporator with the Higher Efficiency for Water Generation.

One of the greenest and promising ways to solve the problem of freshwater crisis is surface solar steam generation from seawater. A great number of photothermal materials with multi-component and multi-layered delicate yet complex structures often suffer from either low evaporation rate or high energy loss. Here, this work presents a single component foam evaporator with steam generation rate of up to 4.32kg m-2 h-1 under 1 sun irradiation. The evaporator is constructed from an aniline oligomer as a single light-absorbing component, covalent linked with polyethylene glycol to form a monolithic polymer foam. Floating on the seawater, the foam has absorbance of 99.5% over the entire solar spectral range and low thermal conductivity (0.0077W K-1m-1) that effectively retains heat in the material and at the interface. After 3 months of continuous outdoor natural sunlight irradiation, the evaporator maintains a stable and durable evaporation rate. Moreover, the materials have good mechanical properties (7.48MPa young's modulus and 57.38% elongation at break) and excellent chemical resistance in 10 common organic solvents and aqueous solutions of pH = 1 to 14. This study provides a new system and strategy for desalination, steam power generation, treatment of polluted water and sewage, etc.

Flexible Multimodal Magnetoresistive Sensors Based on Alginate/Poly(vinyl alcohol) Foam with Stimulus Discriminability for Soft Electronics Using Machine Learning.

Flexible foam-based sensors have attracted substantial interest due to their high specific surface area, light weight, superior deformability, and ease of manufacture. However, it is still a challenge to integrate multimodal stimuli-responsiveness, high sensitivity, reliable stability, and good biocompatibility into a single foam sensor. To achieve this, a magnetoresistive foam sensor was fabricated by an in situ freezing-polymerization strategy based on the interpenetrating networks of sodium alginate, poly(vinyl alcohol) in conjunction with glycerol, and physical reinforcement of core-shell bidisperse magnetic particles. The assembled sensor exhibited preferable magnetic/strain-sensing capability (GF ≈ 0.41 T-1 for magnetic field, 4.305 for tension, -0.735 for bending, and -1.345 for pressing), quick response time, and reliable durability up to 6000 cycles under external stimuli. Importantly, a machine learning algorithm was developed to identify the encryption information, enabling high recognition accuracies of 99.22% and 99.34%. Moreover, they could be employed as health systems to detect human physiological motion and integrated as smart sensor arrays to perceive external pressure/magnetic field distributions. This work provides a simple and ecofriendly strategy to fabricate biocompatible foam-based multimodal sensors with potential applications in next-generation soft electronics.

Dynamic Analysis and Optimization on Passive/Active Vibration Reduction of a Beam Structure with Distributed Smart Foams

A smart foam is a vibration absorption structure integrated with piezoelectric material and shows promise for a highly efficient structural vibration reduction both passively and actively. The arrangement of the smart foams on the primary structure is a key issue in practical engineering. In this work, the vibration reduction performances of distributed smart foams attached to a simply supported beam are investigated, and the distribution scheme is optimized. The dynamic equations of the vibration system are established for passive and active vibration reduction, respectively. The frequency responses are analyzed based on a Newmark-[Formula: see text] method, and the accuracy is verified by a finite element analysis. An optimization method based on the genetic algorithm is proposed for the smart foams’ quantity and locations. The study reveals that, with the same total attached mass (1% of the beam mass), a limited distribution of smart foams achieves a larger vibration reduction ratio than a single smart foam or uniformly distributed smart foams. For the passive reduction mode, the optimal scheme is to arrange four smart foams at the middle of the beam, and a reduction ratio of 38% is achieved. It is related to both the first-order modal shape of the beam and the mass distribution of smart foams. For the active reduction mode, the optimal scheme is to arrange two smart foams separately, and 98% of the vibration is reduced. The optimal location is no longer at the middle of the beam, because the active moment of the piezoelectric beam makes the main contribution, rather than the passive vibration absorption. This research provides an optimization method and instructions for both passive and active vibration reductions of smart foams.

Fabrication of Two-Layer Aluminum Foam Consisting of Dissimilar Aluminum Alloys Using Optical Heating.

Aluminum foam is a lightweight material and has excellent shock-absorbing properties. Various properties of aluminum foam can be obtained by changing the base aluminum alloy. Multi-layer aluminum foam can be fabricated by varying the alloy type of the base aluminum alloy, but with different foaming temperatures, within a single aluminum foam to achieve multiple properties. In this study, we attempted to fabricate a two-layer aluminum foam with the upper layer of a commercially pure aluminum A1050 foam and the lower layer of an Al-Si-Cu aluminum alloy ADC12 foam by using an optical heating device that can heat from both the upper and lower sides. Two types of heating methods were investigated. One is to directly stack the A1050 precursor coated with black toner on top of the ADC12 precursor and to foam it from the top and bottom by optical heating. The other is to place a wire mesh between the ADC12 precursor and the A1050 precursor and place the A1050 precursor on the wire mesh, thereby creating a space between the precursors, which is then foamed by optical heating from the top and bottom. It was shown that both precursors can be foamed and joined, and a two-layer A1050/ADC12 foam can be fabricated for both types of heating methods. In the method in which two precursors were stacked and foamed, even if the light intensity of the halogen lamps on the top and bottom were adjusted, heat conduction occurred between the stacked precursors, and the foaming of each precursor could not be controlled, resulting in tilting of the joining interface. In the method of foaming using a wire mesh with a gap between two precursors, it was found that by adjusting the light intensity, the two precursors can be foamed almost simultaneously and achieve similar pore structures. The joining interface can also be maintained horizontally.

Numerical investigation of the carrying capacity of single polyurethane foam pile in clay and sand soils

The definition of soil stabilization is a method to enhance the engineering properties. Polyurethane grout is one of the least expensive methods and can be used in construction. Polyurethane injection resin systems for crack injection, slab lifting, soil stabilization, leak sealing, and structural crack repair have been used for the last two decades. Polyurethane foam hasn't been used or understood as a loaded structural element in soils like as embedded piles. In this piece of work, a trial was made to numerically study the behavior of polyurethane foam when used as piles embedded in the clay and sand soils. Plaxis 3D software was adopted to carry out this study. Polyurethane piles of varying diameters and lengths were modelled as embedments in the clay and sand soil, and then incremental loads were applied. Moreover, the study involved the behavior of polyurethane piles when the clay strength was increased. The results indicated that embedded pile resistance to loading increased with the increase in length and pile diameter. When the loading results of polyurethane foam embedded in loose sand are compared with the loading results of piles in soft clay, the ultimate capacity of piles in loose sand, was much higher than that in soft clay. The results also indicated that the polyurethane pile load-carrying capacity increased when L/D ratio decreased for both soft and stiff clay. In this study concrete piles in clay and sand soil were modelled to examine the percentage of loading capacity of concrete piles to that of polyurethane piles for clay and sand soil.

Additive manufacturing of functionally graded foams: Material extrusion process design, part design, and mechanical testing

Functionally graded foams (FGFs) were in-situ fabricated via material extrusion (MEX) additive manufacturing (AM) process. Foamable filaments loaded with thermally expandable microspheres (TEMs) at 8.0 wt% was first fabricated using a single screw extruder. The correlations between the resultant foam density and process factors, namely nozzle temperature (NT) and flow rate (FR) were established using a statistical analysis and the density predictability of the model was verified by experiment. With concurrent control of NT and FR, FGFs with density ranges as high as 0.86 g cm−3 were achieved within a single print. Various FGFs were designed using linear, concave, and convex density gradient functions. The density-process correlation model was then used to obtain the NT and FR parameters needed to produce the density values as demanded by the part design. FGFs along with their single density foam (SDF) counterparts were successfully printed with good dimensional stability. Under quasi-static compression testing, all FGFs showed higher energy absorption capacity at low stress levels, as compared to their SDF counterparts. Moreover, under impact conditions, a significant loading direction dependency was found for the FGFs. Overall, this work demonstrates the AM feasibility of FGFs as a single print with tailored density profiles which can be used in generative design optimization of AM parts for enhanced mechanical performance and other functionalities.

Study on Highly Stable Biomass Gel Foam with Ultra-Strong Film-Forming Performance Based on the Double Network Structure to Inhibit Coal Spontaneous Combustion

ABSTRACT To further enhance gel foam stability, an ultra-strong film-forming stabilized biomass gel foam (PE/SA-Ca) with the double network structure was achieved by using pectin (PE), sodium alginate (SA), calcium L-lactate (Ca-L) and biomass foaming systems (BS). The results showed that the double network gel foam had ultra-strong film-forming and stability performances than the single network gel foam. Specifically, when the PE:SA ratio of the double network gel matrix was 5:5, the film thickness of PE/SA-Ca increased from 1 to 4.25 mm and the half-life increased from 3 to 22 days compared to the single network gel foam. In addition, PE/SA-Ca could maintain film integrity at high temperature up to 120°C. The water retention rate of PE/SA-Ca was increased by 79.5% compared to pure foam. The inhibition rate of PE/SA-Ca in the coal low-temperature oxidation experiment was as high as 78.06% at 180°C. Fire extinguishing experiment showed that PE/SA-Ca could rapidly reduce the coal fire temperature from 960 to 68.9°C within 20 min and effectively prevent prevention of coal re-ignition. This research provides a technical method for the development of highly stable, ultra-strong film-forming and eco-friendly gel foam.

Continuous-wave terahertz in-line holographic diffraction tomography with the scattering fields reconstructed by a physics-enhanced deep neural network

Diffraction tomography is a promising, quantitative, and nondestructive three-dimensional (3D) imaging method that enables us to obtain the complex refractive index distribution of a sample. The acquisition of the scattered fields under the different illumination angles is a key issue, where the complex scattered fields need to be retrieved. Presently, in order to develop terahertz (THz) diffraction tomography, the advanced acquisition of the scattered fields is desired. In this paper, a THz in-line digital holographic diffraction tomography (THz-IDHDT) is proposed with an extremely compact optical configuration and implemented for the first time, to the best of our knowledge. A learning-based phase retrieval algorithm by combining the physical model and the convolution neural networks, named the physics-enhanced deep neural network (PhysenNet), is applied to reconstruct the THz in-line digital hologram, and obtain the complex amplitude distribution of the sample with high fidelity. The advantages of the PhysenNet are that there is no need for pretraining by using a large set of labeled data, and it can also work for thick samples. Experimentally with a continuous-wave THz laser, the PhysenNet is first demonstrated by using the thin samples and exhibits superiority in terms of imaging quality. More importantly, with regard to the thick samples, PhysenNet still works well, and can offer 2D complex scattered fields for diffraction tomography. Furthermore, the 3D refractive index maps of two types of foam sphere samples are successfully reconstructed by the proposed method. For a single foam sphere, the relative error of the average refractive index value is only 0.17%, compared to the commercial THz time-domain spectroscopy system. This demonstrates the feasibility and high accuracy of the THz-IDHDT, and the idea can be applied to other wavebands as well.

Balance Error Scoring System Performance Differences in Figure Skaters Based on Discipline.

Balance and postural stability are required of figure skaters throughout on-ice performance. Spinning, jumping, and landing each rely on this skill set to maintain control while skaters manage changing demands for each skating discipline. The aim of this study was to compare balance error scoring system (BESS) performance in figure skaters between disciplines and determine if age was related to BESS performance. Cross-sectional study. Three hundred and fifty-eight figure skaters (age: 15.4±3.3 years, 213 females, 145 males) of multiple disciplines completed the BESS during the United States Figure Skating's Standardized Testing of Athleticism to Recognize Skaters (S.T.A.R.S.) combine. Errors during each condition of the BESS were recorded by trained evaluators. A 3x6 ANOVA was used to determine BESS differences based on skating discipline. Spearman's rho (ρ) correlation coefficients were calculated for relationships between BESS errors and age. Ice dancers had more errors than singles and pairs for bipedal foam (p<0.001) but had fewer errors than single skaters for single leg foam (p=0.002). Tandem on a firm surface also showed an increase in errors for ice dancers and pairs skaters compared to singles (p<0.001). There were significant weak negative relationships noted between age and bipedal foam and single leg firm conditions (ρ=-0.14, -0.23, p<0.05). Figure skaters of different disciplines have varying levels of static postural stability. Assessing postural stability in figure skaters can provide insight to improve performance and may identify skaters at risk of injury. 3©The Author(s).

Crashworthiness Analysis of Vehicle Crash-Box Filled with Aluminium Foam

Lightweight, robust, and anti-rust properties of aluminium foam might be a solution for reducing the effect of traffic accidents and for minimum fuel consumption. This research investigated the crashworthiness of vehicle crash-box filled with aluminum foam by varying its cross-sectional structure and its loading angle such as 0°, 10°, 20°, 30°. The variations consisted of structures for example single wall foam filled and double wall foam filled. The material used to construct the wall was Aluminum Alloy 2024 and Aluminium foam. The finite element model using Abaqus CAE Software was operated for both designing the crash-box and analyzing its crashworthiness. Some parameters were determined To obtain the best crash-box design, the finite element analysis was carried on total energy absorption, specific energy absorption, maximum load, average load, and crush-force efficiency. Double wall foam filled crash-box was shown to have better energy absorption ability and this structure of crush box is considered fpr vehicle structure in future.

Single dose intralesional doxycycline foam infusion promotes bone growth and resolution of an odontoid aneurysmal bone cyst

Aneurysmal bone cysts (ABCs) are locally invasive bone tumors that most commonly arise in long bone metaphyses, the vertebral column, and pelvis, often presenting in the second decade of life. ABCs can be treated with resection, radiation, arterial embolization, and intralesional curettage. More recently intralesional doxycycline foam injections, which appear to act through the inhibition of matrix metalloproteinases and angiogenesis, have been used successfully, although multiple treatments are often required with this approach.A 13-year-old male with an incidentally discovered ABC filling much of the odontoid process but not violating the native odontoid cortex was treated with a single intralesional doxycycline foam injection delivered through a transoral approach with an excellent radiographic result. After placing a Crowe-Davis retractor, a transoral exposure of the odontoid process was performed with neuronavigation guidance. A fluoroscopy-guided Jamshidi needle biopsy was performed and via the needle doxycycline foam (2 mL 50 mg/mL doxycycline, 2 mL 25% albumin, and 1 mL Isovue 370 mixed with 5 mL of air) was infused, filling the cystic cavities of the odontoid process. The patient tolerated the operation well. Two months postoperatively, a computed tomography (CT) scan demonstrated a decrease in the size of the lesion with substantial new bone formation. Repeat CT at 6 months showed no residual cystic lucency, formation of dense new bone, and only minimal irregularity of the cortex at the prior needle biopsy site.This case illustrates that the use of doxycycline foam can be an excellent option when managing ABCs that cannot be resected without incurring significant morbidity.

Dual layered light weight fire resistant PU foam-based composite for acoustical insulation

In today's automotive industry, sound package design and optimization is important considering the mounting need for weight reduction and achieving targeted sound absorption and sound transmission loss values. The present paper relates to dual layered light weight (LW) fire resistant (FR) Polyurethane (PU) foam-based composite for engine room insulation, referred herein as Ωµ2 foam comprising of two layers of foam having different densities and flexibility. The composite consists of one layer of semirigid FR PU foam acting as a carrier with sound absorptive property and another layer consisting of flexible FR PU foam acting as higher acoustical absorptive property. This concept is intended for enhancement of acoustical performance by the synergistic effect of dual foam layers besides being FR and LW material, specially designed for passenger vehicles' engine compartment insulations such as firewall/dash panel, bonnet/hood liner insulation and other diverse applications in commercial vehicles. The paper presents material properties and in-depth comparative assessment of sound absorption properties of dual layer (Ωµ2) LW FR PU foam with respect to conventional materials like single layer light weight semi-rigid PU foam and resinated cotton shoddy felt, etc.

Sheath-Based Combined Foam Sclerotherapy to Promote Management of Extensive Insufficiency of the Great Saphenous Vein in Venous Ulcers.

Background: Foam sclerotherapy is considered an acceptable method to treat great saphenous vein (GSV) insufficiency, promoting occlusion of its trunk and eradicating reflux. Various modalities and techniques have been described, varying form foam infusion through multiple short cannulae along the GSV to catheter-directed techniques in order to facilitate complete proximal GSV occlusion and improve technical and clinical success. Purpose: To present a modification of the sclerotherapy tehcnique where the presence of venous ulcers poses an extra challenge to the treatment of GSV treatment. Technique: We describe a technical proposal of single foam perfusion through a 11cm 5F sheath placed at the knee level combined with simultaneous retrograde infusion below the knee. Perivenous tumescent segmental infiltration with cold normal saline at 4°C is applied initially to reduce the diameter in those GSV >6-7mm. Conclusions: This combination avoids multiple vein cannulation in the GSV along the thigh as well as the need for antegrade infusion when GSV cannulation at the lower tibia is prohibited by a large ulcer area.

Ultrathin Micellar Foam Films of Sodium Caseinate Protein Solutions

Sodium caseinates (NaCas), derived from milk proteins called caseins, are often added to food formulations as emulsifiers, foaming agents, and ingredients for producing dairy products. In this contribution, we contrast the drainage behavior of single foam films made with micellar NaCas solutions with well-established features of stratification observed for the micellar sodium dodecyl sulfate (SDS) foam films. In reflected light microscopy, the stratified SDS foam films display regions with distinct gray colors due to differences in interference intensity from coexisting thick-thin regions. Using IDIOM (interferometry digital imaging optical microscopy) protocols we pioneered for mapping nanotopography of foam films, we showed that drainage via stratification in SDS films proceeds by the expansion of flat domains that are thinner than surrounding by a concentration-dependent step-size, and nonflat features (nanoridges and mesas) form at the moving front. Furthermore, stratifying SDS foam films show stepwise thinning, such that the step-size and terminal film thickness decrease with concentration. Here we visualize the nanotopography in protein films with high spatiotemporal resolution using IDIOM protocols to address two long-standing questions. Do protein foam films formulated with NaCas undergo drainage via stratification? Are thickness transitions and variations in protein foam films determined by intermicellar interactions and supramolecular oscillatory disjoining pressure? In contrast with foam films containing micellar SDS, we find that micellar NaCas foam films display just one step, nonflat and noncircular domains that expand without forming nanoridges and a terminal thickness that increases with NaCas concentration. We infer that the differences in adsorbing and self-assembling unimers triumph over any similarities in the structure and interactions of their micelles.

Repulsive, but sticky – Insights into the non-ionic foam stabilization mechanism by superchaotropic nano-ions

HypothesisThe superchaotropic Keggin polyoxometalate α-SiW12O404− (SiW) was recently shown to stabilize non-ionic surfactant (C18:1E10) foams owing to electrostatic repulsion that arises from the adsorption of SiW-ions to the foam interfaces. The precise mechanism of foam stabilization by SiW however remained unsolved. ExperimentsImaging and conductimetry were used on macroscopic foams to monitor the foam collapse under free drainage and small angle neutron scattering (SANS) at a given foam height allowed for the tracking of the evolution of film thickness under quasi-stationary conditions. Thin film pressure balance (TFPB) measurements enabled to quantify the resistance of single foam films to external pressure and to identify intra-film forces. FindingsAt low SiW/surfactant ratios, the adsorption of SiW induces electrostatic repulsion within foam films. Above a concentration threshold corresponding to an adsorption saturation, excess of SiW screens the electrostatic repulsion that leads to thinner foam films. Despite screened electrostatics, the foam and single foam films remain very stable caused by an additional steric stabilizing force consistent with the presence of trapped micelles inside the foam films that bridge between the interfaces. These trapped micelles can serve as a surfactant reservoir, which promotes self-healing of the interface leading to much more resilient foam films in comparison to bare surfactant foams/films.