Hierarchical bubble size distributions in coarsening wet liquid foams.

Coarsening of two-phase systems is crucial for the stability of dense particle packings such as alloys, foams, emulsions, or supersaturated solutions. Mean field theories predict an asymptotic scaling state with a broad particle size distribution. Aqueous foams are good model systems for investigations of coarsening-induced structures, because the continuous liquid as well as the dispersed gas phases are uniform and isotropic. We present coarsening experiments on wet foams, with liquid fractions up to their unjamming point and beyond, that are performed under microgravity to avoid gravitational drainage. As time elapses, a self-similar regime is reached where the normalized bubble size distribution is invariant. Unexpectedly, the distribution features an excess of small roaming bubbles, mobile within the network of jammed larger bubbles. These roaming bubbles are reminiscent of rattlers in granular materials (grains not subjected to contact forces). We identify a critical liquid fraction [Formula: see text], above which the bubble assembly unjams and the two bubble populations merge into a single narrow distribution of bubbly liquids. Unexpectedly, [Formula: see text] is larger than the random close packing fraction of the foam [Formula: see text]. This is because, between [Formula: see text] and [Formula: see text], the large bubbles remain connected due to a weak adhesion between bubbles. We present models that identify the physical mechanisms explaining our observations. We propose a new comprehensive view of the coarsening phenomenon in wet foams. Our results should be applicable to other phase-separating systems and they may also help to control the elaboration of solid foams with hierarchical structures.

Multiscale Design for Robust, Thermal Insulating, and Flame Self-Extinguishing Cellulose Foam.

Cellulose foams are in high demand in an era of prioritizing environmental consciousness. Yet, transferring the exceptional mechanical properties of cellulose fibers into a cellulose network remains a significant challenge. To address this challenge, an innovative multiscale design is developed for producing cellulose foam with exceptional network integrity. Specifically, this design relies on a combination of physical cross-linking of the microfibrillated cellulose (MFC) networks by cellulose nanofibril (CNF) and aluminum ion (Al3+), as well as self-densification of the cellulose induced by ice-crystal templating, physical cross-linking, solvent exchange, and evaporation. The resultant cellulose foam demonstrates a low density of 40.7 mg cm-3, a high porosity of 97.3%, and a robust network with high compressive modulus of 1211.5 ± 60.6 kPa and energy absorption of 77.8 ± 1.9 kJ m-3. The introduction of CNF network and Al3+ cross-linking into foam also confers excellent wet stability and flame self-extinguish ability. Furthermore, the foam can be easily biodegraded in natural environments , re-entering the ecosystem's carbon cycle. This strategy yields a cellulose foam with a robust network and outstanding environmental durability, opening new possibilities for the advancement of high-performance foam materials.

Nontarget Analysis Combined with TOP Assay Reveals a Significant Portion of Unknown PFAS Precursors in Firefighting Foams Currently Used in China.

Firefighting foam is a significant source of per- and polyfluoroalkyl substances (PFAS) pollution, yet the PFAS profiles in foam formulations, particularly in China, remain unclear. Here, using target and nontarget analyses, we investigated 50 target PFAS in firefighting foams currently utilized in China, identified novel PFAS, and discovered new end products through a total oxidizable precursor (TOP) assay. We identified a total of 54 PFAS compounds (spanning 34 classes and containing seven novel PFAS) with total PFAS concentrations of 0.03-21.21 mM. Among seven novel PFAS, four PFAS met persistence, bioaccumulation, and toxicity criteria, and another PFAS had the highest ToxPi score among the identified 54 PFAS. Moreover, the predominant PFAS varied significantly in the studied foams and differed markedly from those used in other countries. After the TOP assay, nontarget analysis uncovered 1.1-55.5% more PFAS precursors and 8.25-55.5% more fluorine equivalents compared to traditional target analysis combined with TOP assay. Specifically, three double-bond perfluorinated alcohols were identified for the first time as end products of the TOP assay. This study provides crucial information for pollution control and risk assessment associated with PFAS in firefighting foam applications and emphasizes the importance of combining nontarget analysis with TOP assay in uncovering unknown PFAS precursors.

Stability and Biotransformation of 6:2 Fluorotelomer Sulfonic Acid, Sulfonamide Amine Oxide, and Sulfonamide Alkylbetaine in Aerobic Sludge.

The 6:2 fluorotelomer sulfonamide (6:2 FTSAm)-based compounds signify a prominent group of per- and polyfluoroalkyl substances (PFAS) widely used in contemporary aqueous film-forming foam (AFFF) formulations. Despite their widespread presence, the biotransformation behavior of these compounds in wastewater treatment plants remains uncertain. This study investigated the biotransformation of 6:2 FTSAm-based amine oxide (6:2 FTNO), alkylbetaine (6:2 FTAB), and 6:2 fluorotelomer sulfonic acid (6:2 FTSA) in aerobic sludge over a 100-day incubation period. The biotransformation of 6:2 fluorotelomer sulfonamide alkylamine (6:2 FTAA), a primary intermediate product of 6:2 FTNO, was indirectly assessed. Their stability was ranked based on the estimated half-lives (t1/2): 6:2 FTAB (no obvious products were detected) ≫ 6:2 FTSA (t1/2 ≈28.8 days) > 6:2 FTAA (t1/2 ≈11.5 days) > 6:2 FTNO (t1/2 ≈1.2 days). Seven transformation products of 6:2 FTSA and 15 products of 6:2 FTNO were identified through nontarget and suspect screening using high-resolution mass spectrometry. The transformation pathways of 6:2 FTNO and 6:2 FTSA in aerobic sludge were proposed. Interestingly, 6:2 FTSAm was hardly hydrolyzed to 6:2 FTSA and further biotransformed to perfluoroalkyl carboxylic acids (PFCAs). Furthermore, the novel pathways for the generation of perfluoroheptanoic acid (PFHpA) from 6:2 FTSA were revealed.

Solidification of Polyurethane Model Foams via Catalyst Drainage from a Secondary Foam.

Due to their unique mechanical and thermal properties, polyurethane foams are widely used in multiple fields of applications, including cushioning, thermal insulation or biomedical engineering. However, the way polyurethane foams are usually manufactured - via chemical foaming - produces samples where blowing and gelling occur at the same time, resulting in a morphology control achieved by trial and error processes. Here, a novel strategy is introduced to build model homogeneous polyurethane foams of controlled density with millimetric bubbles from liquid templates. By producing a polyurethane foam via physical bubbling without a catalyst and gently depositing a secondary foam containing catalyst on the top of this first foam, it is possible to take advantage of drainage mechanisms to trigger the solidification of the bottom foam. The characterization of the samples performed by X-ray microtomography allows to study quantitatively the structure of the final solid foam, at the global and at the local scale. Using the tomographic 3D images of the foam architectures, the superimposed foam technique introduced in this article is shown to be promising to produce foams with a good homogeneity along the vertical direction, with a density controlled by varying the concentration of catalyst in the secondary foam.

Foam film stratification studies probe intermicellar interactions.

Ultrathin foam films containing supramolecular structures like micelles in bulk and adsorbed surfactant at the liquid-air interface undergo drainage via stratification. At a fixed surfactant concentration, the stepwise decrease in the average film thickness of a stratifying micellar film yields a characteristic step size that also describes the quantized thickness difference between coexisting thick-thin flat regions. Even though many published studies claim that step size equals intermicellar distance obtained using scattering from bulk solutions, we found no reports of a direct comparison between the two length scales. It is well established that step size is inversely proportional to the cubic root of surfactant concentration but cannot be estimated by adding micelle size to Debye length, as the latter is inversely proportional to the square root of surfactant concentration. In this contribution, we contrast the step size obtained from analysis of nanoscopic thickness variations and transitions in stratifying foam films using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols, that we developed, with the intermicellar distance obtained using small-angle X-ray scattering. We find that stratification driven by the confinement-induced layering of micelles within the liquid-air interfaces of a foam film provides a sensitive probe of non-DLVO (Derjaguin-Landau-Verwey-Overbeek) supramolecular oscillatory structural forces and micellar interactions.

Bio-based polyester-polyurethane foams: synthesis and degradability by Aspergillus niger and Aspergillus clavatus.

In this article, the degradability by Aspergillus niger and Aspergillus clavatus of three bio-based polyurethane (PU) foams is compared to previous degradability studies involving a Pseudomonas sp. bacterium and similar initial materials (Spontón et al. in Int. Biodet. Biodeg. 85:85-94, 2013, https://doi.org/10.1016/j.ibiod.2013.05.019 ). First, three new polyester-polyurethane foams were prepared from mixtures of castor oil (CO), maleated castor oil (MACO), toluene diisocyanate (TDI), and water. Then, their degradation tests were carried out in an aqueous medium, and employing the two mentioned fungi, after their isolation from the environment. From the degradation tests, the following was observed: (a) the insoluble (and slightly collapsed) foams exhibited free hydroxyl, carboxyl, and amine moieties; and (b) the water soluble (and low molar mass) compounds contained amines, carboxylic acids, and glycerol. The most degraded foam contained the highest amount of MACO, and therefore the highest concentration of hydrolytic bonds. A basic biodegradation mechanism was proposed that involves hydrolysis and oxidation reactions.

Efficient recycling pathway of bio-based composite polyurethane foams via sustainable diamine.

Aminolysis is widely recognized as a valuable chemical route for depolymerizing polymeric materials containing ester, amide, or urethane functional groups, including polyurethane foams. Bio-based polyurethane foams, pristine and reinforced with 40 wt% of sustainable fillers, were depolymerized in the presence of bio-derived butane-1,4-diamine, BDA. A process comparison was made using fossil-derived ethane-1,2-diamine, EDA, by varying amine/polyurethane ratio (F/A, 1:1 and 1:0.6). The obtained depolymerized systems were analyzed by FTIR and NMR characterizations to understand the effect of both diamines on the degradation pathway. The use of bio-based BDA seemed to be more effective with respect to conventional EDA, owing to its stronger basicity (and thus higher nucleophilicity), corresponding to faster depolymerization rates. BDA-based depolymerized systems were then employed to prepare second-generation bio-based composite polyurethane foams by partial replacement of isocyanate components (20 wt%). The morphological, mechanical, and thermal conductivity properties of the second-generation polyurethane foams were evaluated. The best performances (σ10 %=71 ± 9 kPa, λ = 0.042 ± 0.015 W∙ m-1 ∙K-1) were attained by employing the lowest F/A ratio (1:0.6); this demonstrates their potential application in different sectors such as packaging or construction, fulfilling the paradigm of the circular economy.

Advancements in Detection and Mitigation Strategies for Petroleum-Derived Contaminants in Aquatic Environments: A Comprehensive Review.

The exponential increase in the production and transportation of petroleum-derived products observed in recent years has been driven by the escalating demand for energy, textiles, plastic-based materials, and other goods derived from petroleum. Consequently, there has been a corresponding rise in spills of these petroleum derivatives, particularly in water sources utilized for transportation or, occasionally, illegally utilized for tank cleaning or industrial equipment maintenance. Numerous researchers have proposed highly effective techniques for detecting these products, aiming to facilitate their cleanup or containment and thereby minimize environmental pollution. However, many of these techniques rely on the identification of individual compounds, which presents significant drawbacks, including complexity of handling, subjectivity, lengthy analysis times, infeasibility for in situ analysis, and high costs. In response, there has been a notable surge in the utilization of sensors or generalized profiling techniques serving as sensors to generate characteristic fingerprints of these products, thereby circumventing the aforementioned disadvantages. This review comprehensively examines the evolution of techniques employed for detecting petroleum-derived products in water samples, along with their associated advantages and disadvantages. Furthermore, the review examines current perspectives on methods for the removal and/or containment of these products from water sources, to minimize their environmental impact and the associated health repercussions on living organisms and ecosystems.

Electric Susceptibility at Partial Coverage of a Circular One-Side Access Capacitive Sensor with Rigid Polyurethane Foams.

The capability of dielectric measurements was significantly increased with the development of capacitive one-side access physical sensors. Complete samples give no opportunity to study electric susceptibility at a partial coverage of the one-side access sensor's active area; therefore, partial samples are proposed. The electric susceptibility at the partial coverage of a circular one-side access sensor with cylinders and shells is investigated for polyurethane materials. The implementation of the relative partial susceptibility permitted us to transform the calculated susceptibility data to a common scale of 0.0-1.0 and to outline the main trends for PU materials. The partial susceptibility, relative partial susceptibility, and change rate of relative partial susceptibility exhibited dependence on the coverage coefficient of the sensor's active area. The overall character of the curves for the change rate of the relative partial susceptibility, characterised by slopes of lines and the ratio of the change rate in the centre and near the gap, corresponds with the character of the surface charge density distribution curves, calculated from mathematical models. The elaborated methods may be useful in the design and optimization of capacitive OSA sensors of other configurations of electrodes, independent of the particular technical solution.

Polydopamine/chitosan hydrogels-functionalized polyurethane foams in situ decorated with silver nanoparticles for water disinfection.

A new facile route to decorate polyurethane foams (PUF) with dense and uniform silver nanoparticles (AgNPs) to ensure efficient and long-term water disinfection is proposed. The antibacterial sponge was fabricated by sequential treatment with chitosan hydrogels grafting, polydopamine (PDA) coating, and finally in situ growth of AgNPs on the surface of substrate. The morphologies, chemical composition, crystalline nature, mechanical property, and swelling capacity of the composite were characterized. Its silver release behavior and bactericidal performances against Escherichia coli (E. coli) were evaluated. Results show that the composite demonstrated higher mechanical strength (compression strength, 51.34 kPa) and a rapid swelling rate with an equilibrium swelling ratio of 18.2 g/g. It possessed a higher loading amount of AgNPs (35.87 mg/g) than that of PUF@Ag (8.21 mg/g) and restricted the cumulative silver release of below 0.05% after 24-h immersion in water. Besides, it presented efficient bactericidal activity with complete reduction of E. coli with 10 min of contact time. The strong bactericidal action was probably governed by strengthening the contact between AgNPs immobilized on the substrate and bacteria cells. Furthermore, the composite demonstrated exceptional reusability for five cycles and exhibited a superior processing capacity in the flow test. Finally, the composite could effectively disinfect the natural water sample like a river in 30 min under real conditions.

Feasibility analysis of continuous extraction of biomaterials from flocculant sludge and potential applications in the fire protection field.

The sludge contains many high-value biological materials. However, current extraction methods focus only on individual materials, neglecting the further extraction potential of the residual after extraction. This study used continuous extraction to extract extracellular polymeric substances (EPS) and proteins (PN) from sludge, verified the flame retardancy of EPS and the foaming properties of PN and finally analyzed the economic feasibility of continuous extraction. The results showed that continuous extraction increased the protein extraction from 857.11 mg/L to 1089.41 mg/L. EPS reduced the heat release rate of linen fabric from 379.2 (J/g·K) to 38.3 (J/g·K), and PN achieved foaming capacity and stability reaching 770% and 71%, meeting the standards of foam extinguishing agents. The binding form of EPS with linen fabric and the peptide content in PN are crucial factors affecting their application effectiveness. Economic analysis showed that continuous extraction reduced processing costs by 37.64% compared to traditional sludge disposal methods.

Nonconventional Fluorescent Non-Isocyanate Polyurethane Foams for Multipurpose Sensing Applications.

Fluorescent foams with interconnected pores are attractive for the detection and quantification of various products. However, many fluorescent probes are suffering from aggregation-caused fluorescence quenching in their solid/aggregated state, are costly, and/or not straightforward to incorporate in foams, limiting their utility for this application. Herein, non-isocyanate polyurethane foams, prepared by the simple water-induced self-blowing process, present a nonconventional fluorescence behaviour, i.e. they are intrinsically fluorescent with a multicolor emission without requiring ex-situ traditional fluorescent probes. These foams demonstrate utility for capturing-sensing gaseous formaldehyde (an emblematic indoor air pollutant), as well as for detecting and quantifying various metal ions (Fe2+, Cu2+, Fe3+, Hg2+). They are also able to selectively sense tetracycline antibiotic in a ratiometric way with a high sensitivity. By exploiting the unique multicolor photoluminescent foam properties, a smartphone-compatible device is used for the facile antibiotic quantification. This nonconventional fluorescence behaviour is discussed experimentally and theoretically, and is mainly based on clusteroluminescence originating from multiple hydrogen bonding and hetero-atomic sub-luminophores, thus from aggregation-induced emission luminogens that are naturally present in the foams. This work illustrates that easily accessible non-conventional fluorescent NIPU foams characterized by a modular emission wavelength have an enormous potential for multiple substrates detection and quantification.

Triple Stimuli-Responsive Flexible Shape Memory Foams with Super-Amphiphilicity.

Highly porous multi-responsive shape memory foams have unique advantages in designing 3D materials with lightweight for varied applications. Herein, a facile and efficient approach to fabricating a thermo-, electro-, and photo-responsive shape memory composite foam is demonstrated. A specific multi-step carbonization protocol is adopted for transforming commercial melamine sponge (MS) to highly porous carbon foam (CF) with robust elastic resilience, efficient electrothermal/photothermal conversions, and super-amphiphilicity. It is a novel proposal for CF to take the dual role of the elastic supporting framework and 3D energy conversion/transmission network without any functional fillers. The composite foam cPCL@CF incorporates the CF skeleton with in situ crosslinked polycaprolactone (PCL) layers, which exhibits high conductivity (≈140 S m-1 ) and excellent light absorption (≈97.7%) in the range of 250-2500 nm. By triggering the crystalline transition of PCL, the composite foam displays sensitive electro- and photo-induced shape memory effect (SME) with outstanding shape fixation ratio (Rf ) and recovery ratio (Rr ). Thanks to the super-amphiphilicity and high electrical conductivity, the cPCL@CF composite foam can give rapid and distinguishable electric signals upon tiny drips of salt solutions or lithium-ion battery (LIB) electrolytes, making it a new type of sensor for detecting electrolyte leakage.

Efficient Fabrication of Micro/Nanostructured Polyethylene/Carbon Nanotubes Foam with Robust Superhydrophobicity, Excellent Photothermality, and Sufficient Adaptability for All-Weather Freshwater Harvesting.

The integration of fog collection and solar-driven evaporation has great significance in addressing the challenge of the global freshwater crisis. Herein, a micro/nanostructured polyethylene/carbon nanotubes foam with interconnected open-cell structure (MN-PCG) is fabricated using an industrialized micro extrusion compression molding technology. The 3D surface micro/nanostructure provides sufficient nucleation points for tiny water droplets to harvest moisture from humid air and a fog harvesting efficiency of 1451 mg cm-2 h-1 is achieved at night. The homogeneously dispersed carbon nanotubes and the graphite oxide@carbon nanotubes coating endow the MN-PCG foam with excellent photothermal properties. Benefitting from the excellent photothermal property and sufficient steam escape channels, the MN-PCG foam attains a superior evaporation rate of 2.42 kg m-2 h-1 under 1 Sun illumination. Consequently, a daily yield of ≈35 kg m-2 is realized by the integration of fog collection and solar-driven evaporation. Moreover, the robust superhydrophobicity, acid/alkali tolerance, thermal resistance, and passive/active de-icing properties provide a guarantee for the long-term work of the MN-PCG foam during practical outdoor applications. The large-scale fabrication method for an all-weather freshwater harvester offers an excellent solution to address the global water scarcity.

Synergistically Achieving Superior Sodium Storage of Metal Selenides by Constructing N-Doped Carbon Foams and Utilizing Cu-Driven Replacement Reaction.

Metal selenides are considered as one of the most promising anode materials for Na-ion batteries owing to high specific capacity and relatively higher electronic conductivity compared with metal sulfides or oxides. However, such anodes still suffer from huge volume change upon repeated Na+ insertion/extraction processes and simultaneously undergo severe shuttle effect of polyselenides, thus leading to poor electrochemical performance. Herein, a facile chemical-blowing and selenization strategy to fabricate 3D interconnected hybrids built from metal selenides (MSe, M = Mn, Co, Cr, Fe, In, Ni, Zn) nanoparticles encapsulated in in situ formed N-doped carbon foams (NCFs) is reported. Such hybrids not only provide ultrasmall active nanobuilding blocks (≈15 nm), but also efficiently anchor them inside the conductive NCFs, thus enabling both high-efficiency utilization of active components and high structural stability. On the other hand, Cu-driven replacement reaction is utilized for efficiently inhibiting the shuttle effect of polyselenides in ether-based electrolyte. Benefiting from the combined merits of the unique MSe@NCFs and the utilization of the conversion of metal selenides to copper selenides, the as-obtained hybrids (MnSe as an example) exhibit superior rate capability (386.6 mAh g-1 up to 8 A g-1 ) and excellent cycling stability (347.7 mAh g-1 at 4.0 A g-1 after 1200 cycles).

Carbon Foam-Supported VS2 Cathode for High-Performance Flexible Self-Healing Quasi-Solid-State Zinc-Ion Batteries.

As the new generation of energy storage systems, the flexible battery can effectively broaden the application area and scope of energy storage devices. Flexibility and energy density are the two core evaluation parameters for the flexible battery. In this work, a flexible VS2 material (VS2 @CF) is fabricated by growing the VS2 nanosheet arrays on carbon foam (CF) using a simple hydrothermal method. Benefiting from the high electric conductivity and 3D foam structure, VS2 @CF shows an excellent rate capability (172.8 mAh g-1 at 5 A g-1 ) and cycling performance (130.2 mAh g-1 at 1 A g-1 after 1000 cycles) when it served as cathode material for aqueous zinc-ion batteries. More importantly, the quasi-solid-state battery VS2 @CF//Zn@CF assembled by the VS2 @CF cathode, CF-supported Zn anode, and a self-healing gel electrolyte also exhibits excellent rate capability (261.5 and 149.8 mAh g-1 at 0.2 and 5 A g-1 , respectively) and cycle performance with a capacity of 126.6 mAh g-1 after 100 cycles at 1 A g-1 . Moreover, the VS2 @CF//Zn@CF full cell also shows good flexible and self-healing properties, which can be charged and discharged normally under different bending angles and after being destroyed and then self-healing.

High Persistence of Novel Polyfluoroalkyl Betaines in Aerobic Soils.

Some contemporary aqueous film-forming foams (AFFFs) contain n:3 and n:1:2 fluorotelomer betaines (FTBs), which are often detected at sites impacted by AFFFs. As new chemical replacements, little is known about their environmental fate. For the first time, we investigated the biotransformation potential of 5:3 and 5:1:2 FTBs and a commercial AFFF that mainly contains n:3 and n:1:2 FTBs (n = 5, 7, 9, 11, and 13). Although some polyfluoroalkyl compounds are precursors to perfluoroalkyl acids, 5:3 and 5:1:2 FTBs exhibited high persistence, with no significant changes even after 120 days of incubation. While the degradation of 5:3 FTB into suspected products such as fluorotelomer acids or perfluoroalkyl carboxylic acids (PFCAs) could not be conclusively confirmed, we did identify a potential biotransformation product, 5:3 fluorotelomer methylamine. Similarly, 5:1:2 FTB did not break down or produce short-chain hydrogen-substituted polyfluoroalkyl acids (n:2 H-FTCA), hydrogen-substituted PFCA (2H-PFCA), or any other products. Incubating the AFFF in four soils with differing properties and microbial communities resulted in 0.023-0.25 mol % PFCAs by day 120. Most of the products are believed to be derived from n:2 fluorotelomers, minor components of the AFFF. Therefore, the findings of the study cannot be fully explained by the current understanding of structure-biodegradability relationships.

Uptake of Per- and Polyfluoroalkyl Substances by Fish, Mussel, and Passive Samplers in Mobile-Laboratory Exposures Using Groundwater from a Contamination Plume at a Historical Fire Training Area, Cape Cod, Massachusetts.

Aqueous film-forming foams historically were used during fire training activities on Joint Base Cape Cod, Massachusetts, and created an extensive per- and polyfluoroalkyl substances (PFAS) groundwater contamination plume. The potential for PFAS bioconcentration from exposure to the contaminated groundwater, which discharges to surface water bodies, was assessed with mobile-laboratory experiments using groundwater from the contamination plume and a nearby reference location. The on-site continuous-flow 21-day exposures used male and female fathead minnows, freshwater mussels, polar organic chemical integrative samplers (POCIS), and polyethylene tube samplers (PETS) to evaluate biotic and abiotic uptake. The composition of the PFAS-contaminated groundwater was complex and 9 PFAS were detected in the reference groundwater and 17 PFAS were detected in the contaminated groundwater. The summed PFAS concentrations ranged from 120 to 140 ng L-1 in reference groundwater and 6100 to 15,000 ng L-1 in contaminated groundwater. Biotic concentration factors (CFb) for individual PFAS were species, sex, source, and compound-specific and ranged from 2.9 to 1000 L kg-1 in whole-body male fish exposed to contaminated groundwater for 21 days. The fish and mussel CFb generally increased with increasing fluorocarbon chain length and were greater for sulfonates than for carboxylates. The exception was perfluorohexane sulfonate, which deviated from the linear trend and had a 10-fold difference in CFb between sites, possibly because of biotransformation of precursors such as perfluorohexane sulfonamide. Uptake for most PFAS in male fish was linear over time, whereas female fish had bilinear uptake indicated by an initial increase in tissue concentrations followed by a decrease. Uptake of PFAS was less for mussels (maximum CFb = 200) than for fish, and mussel uptake of most PFAS also was bilinear. Although abiotic concentration factors were greater than CFb, and values for POCIS were greater than for PETS, passive samplers were useful for assessing PFAS that potentially bioconcentrate in fish but are present at concentrations below method quantitation limits in water. Passive samplers also accumulate short-chain PFAS that are not bioconcentrated.

Fabrication of Lightweight Polyimide Foams with Exceptional Mechanical and Thermal Properties.

Lightweight polyimide foams (PIFs) with exceptional thermal resistance and compressive properties are fabricated by heating polyester ammonium salts (PEASs) which are prepared by copolymerizing 4, 4'-diaminobenzanilide (DABA), 4, 4'-diaminodiphenyl methane (MDA) and 3, 3', 4, 4'-benzophenone tetracarboxylic dianhydride (BTDA). Hydrogen bonds are formed between CONH and CO in the PI chains due to the addition of DABA and the melt viscosity of PEAS precursors increase with increasing content of DABA, which is advantageous to bind the foaming gases for cell expansion. The expansion ratio of PEAS precursors is increased from 633% to 1133% when the molar ratio of MDA/DABA is changed from 10:0 to 6:4. The compressive strength and modulus of PIFM9D1 (i.e., the molar ratio of MDA/DABA is 9:1, foam density: 120.8 kg m-3 ) reach as high as 0.59 and 15.0 MPa, respectively. The PIFs possess prominent thermal performance with the initial thermal degradation temperatures (under both nitrogen and air atmosphere) and glass transition temperatures (as assessed by DSC and DMA) exceeding 511 and 292 °C, respectively. The thermal conductivity of PIFs is lower than 0.049 W m-1 K-1 , which exhibits promising applications for serving as high-temperature thermal insulation materials in the fields of aerospace, marine, and nuclear sectors among others.