From hydrogel to aerogel: A green fabrication of multifunctional polyimide absorbents

Evaluation of the release kinetics of hydrophilic and lipophilic compounds from lipid-polymer hybrid nanoparticles

In disease treatment, maintaining therapeutic drug concentrations often requires multiple doses. Lipid/polymer hybrid nanoparticles (LPHNPs) offer a promising solution by facilitating sustained drug delivery within therapeutic ranges. Here, we synthesized poly(lactic-co-glycolic acid) (PLGA) nanoparticles coated with soy lecithin using nanoprecipitation and self-assembly techniques. These nanoparticles were incorporated into gelatin aerogels to ensure uniform distribution and increase the concentration. Our study focused on understanding the release kinetics of hydrophilic (gallic acid) and lipophilic (quercetin) compounds from this system. Nanoparticles exhibited hydrodynamic diameters of 100 ± 15 nm (empty), 153 ± 33 nm (gallic acid-loaded), and 149 ± 21 nm (quercetin-loaded), with encapsulation efficiencies of 90 ± 5% and 70 ± 10% respectively. Gallic acid release followed the Korsmeyer-Peppas kinetics model (n = 1.01), while quercetin showed first-order kinetics. Notably, encapsulated compounds demonstrated delayed release compared to free compounds in gelatin aerogels, illustrating LPHNPs' ability to modulate release profiles independent of the compound type. This study underscores the potential of LPHNPs in optimizing drug delivery strategies for enhanced therapeutic outcomes.

Hydrogel Extinguishants

The exploitation of clean and efficient fire extinguishing materials has substantial implications for improving disaster prevention, mitigation, and relief capabilities, maintaining public safety, and protecting people's lives and property as well as the natural environment. Natural polymer hydrogel with high water containment, excellent film formation, high heat insulation, ecofriendliness, and degradability has huge potential in achieving new breakthroughs for developing clean and efficient fire extinguishing materials and products. In recent years, the exploitation of hydrogel extinguishing materials and the fabrication of products has attracted great attention, gradually replacing traditional fire extinguishing products. In this perspective, an in-depth review of the evolution of hydrogels applied for fire extinguishing and prevention is presented. Firstly, the extinguishing principles of hydrogel extinguishants are explained. Secondly, the preparation strategies and evaluation system of the hydrogel extinguishants are emphatically discussed. Although great progress has been made in developing high-performance hydrogel extinguishants, it remains challenging to develop cost-effective, degradable, and easy-to-use hydrogel extinguishants. Additionally, we highlight the importance of considering the commercial aspects of hydrogel extinguishants. Looking into the future, hydrogel extinguishants are promising, but continued investment in research and development is necessary to overcome the challenges.

Collaboration of two-star nanomaterials: The applications of nanocellulose-based metal organic frameworks composites

Nanocellulose, as the star nanomaterial in carbohydrate polymers, has excellent mechanical properties, biodegradability, and easy chemical modification. However, further practical applications of nanocellulose are limited by their inadequate functionalization. Metal-organic frameworks (MOFs), as the star nanomaterial in functional polymers, have a large surface area, high porosity, and adjustable structure. The collaboration of nanocellulose and MOFs is a desirable strategy to make composites especially interesting for multifunctional and multi-field applications. What sparks will be produced by the collaboration of two-star nanomaterials? In this review article, we highlight an up-to-date overview of nanocellulose-based MOFs composites. The sewage treatment, gas separation, energy storage, and biomedical applications are mainly summarized. Finally, the challenges and research trends of nanocellulose-based MOFs composites are prospected. We hope this review may provide a valuable reference for the development and applications of carbohydrate polymer composites soon.

Mechanically Robust and Flexible GO/PI Hybrid Aerogels as Highly Efficient Oil Absorbents

Herein, mechanically robust and flexible graphene oxide/polyimide (GO/PI) hybrid aerogels (GIAs) were fabricated by a facile method, in which the mixed suspensions of the water-soluble polyimide precursor and graphene oxide (GO) sheets were freeze-dried, which was followed by a routine thermal imidation process. The porous GIAs obtained not only exhibit excellent elasticity and extremely low density values (from 33.3 to 38.9 mg.cm^-3), but they also possess a superior compressive strength (121.7 KPa). The GIAs could support a weight of up to 31,250 times of its own weight, and such a weight-carrying capacity is much higher than that of other typical carbon-based aerogels. Having such a porous structure, and high strength and toughness properties make GIAs ideal candidates for oil spill cleanup materials. The oil/organic solvents' absorption capacity ranges from 14.6 to 85, which is higher than that of most other aerogels (sponges). With their broad temperature tolerance and acidic stability, the unique multifunctional GIAs are expected to further extend their application range into extreme environments.

Organic–Inorganic Double-Gel System Thermally Insulating and Hydrophobic Polyimide Aerogel

Aerogel materials are used in various fields, but there is a shortage of aerogel materials with an excellent combination of mechanical properties, thermal stability, and easy preparation. In this study, polyimide aerogel materials with superior mechanical properties, thermal stability, and low thermal conductivity were prepared by forming a double-gel system in the liquid phase. The amino-modified gel, prepared by coating SiO₂ nano-microspheres with GO through a modified sol-gel method (SiO₂@GO-NH₂), was subsequently homogeneously dispersed with PAA wet gel in water to form a double-gel system. The construction of a double-gel system enabled the PI aerogel to shape a unique honeycomb porous structure and a multi-layered interface of PI/SiO₂/GO. The final obtained PI aerogel possessed effective thermal conductivity (0.0309 W/m·K) and a high specific modulus (46.19 m²/s²). In addition, the high thermal stability (543.80 °C in Ar atmosphere) and the ability to retain properties under heat treatment proved its durability in high thermal environments. The hydrophobicity (131.55°) proves its resistance to water from the environment. The excellent performance of this PI aerogel and its durability in thermal working environments make it possible to be applied in varied industrial and research fields, such as construction and energy, where heat and thermal insulation are required.

Facile and environment-friendly preparation of high-performance polyimide aerogels using water as the only solvent

This study described a facile and environmentally friendly method for preparing polyimide (PI) aerogels via sol-gel process and freeze-drying without the use of organic solvents. The prepared PI aerogels showed...

Combination of an Asphalt Stabilizer and a Cellulose-Chitosan Composite Aerogel Used for the Separation of Oil-Water Mixtures Containing Asphalt

In this paper, cellulose chitosan composite aerogels were prepared through sol-gel and freeze-drying processes. The porous morphology of the aerogels was controlled by adjusting the cellulose concentration. Within a certain range, as the concentration of cellulose increases, the pore diameter of the composite aerogel becomes smaller and the pore structure becomes denser. The cellulose-chitosan composite aerogel can successfully separate the oil-water mixture without asphalt and showed stable filtration performance. The filtration speed is basically unchanged after a slight decrease and can be maintained at about 90% of the initial filtration speed within 30 min. The filtration speed can reach up to 9315 kg·h-1·m-2. When filtering bituminous oil-water mixtures, the filtration rate decreased significantly, with a 50% drop in 30 min. After adding the asphalt stabilizer poly(styrene-alt-octadecyl maleimide) (SNODMI), which is made in our laboratory, the effect of aerogel filtering the asphalt-containing oil-water mixture is obviously improved, and the downward trend of filtration speed is obviously improved. The combination of SNODMI and cellulose-chitosan has great application potential in the field of asphalt-containing oil-water separation.

Fabrication of Elastic Macroporous Polymers with Enhanced Oil Absorbability and Antiwaxing Performance

Porous polymers are of great interest in potential energy storage and environmental remediation applications. However, traditional fabrication methods are either time-consuming or energy-consuming and deteriorate the mechanical strength of polymer materials. In this study, polymerization-induced phase separation was used to realize the template-free fabrication of superflexible macroporous polymers. Since the solvent is also used as a porogen, this method can be widely used to synthesize several porous polymers by carefully choosing the solvent and monomer. Compared to nonstructured polymers, the prepared macroporous polymers exhibited enhanced mechanical strength, superflexibility, multicompressibility, and bending properties. Along with hydrophobicity/oleophilicity and macroporous structures, the as-prepared porous polymers demonstrated controllable oil absorbability and release; furthermore, after infusing with lubrication liquid, these materials can be used as antiwaxing materials. The elastic porous polymers prepared using this simple and universal method show great potential for various applications, including controlled drug release, antiwaxing, and lubrication.

Robust, Lightweight, Hydrophobic, and Fire-Retarded Polyimide/MXene Aerogels for Effective Oil/Water Separation

Polyimide (PI) aerogels have attracted great attention owing to their low density and excellent thermal stability. However, hydrophobic surface modification is required for PI aerogels to improve their ability in oil/water separation due to their amphiphilic characteristic. Two-dimensional MXenes (transition metal carbides/nitrides) can be utilized as nanofillers to enhance the properties of polymers because of their unique layered structure and versatile interface chemistry. Herein, the robust, lightweight, and hydrophobic PI/MXene three-dimensional architectures were fabricated via freeze-drying of polyamide acid/MXene suspensions and thermal imidization. Polyamide acid was synthesized using N-N-dimethylacetamide and 4,4'-oxydianiline. MXene (Ti₃C₂T_x) dispersion was obtained via the etching of Ti₃AlC₂ and ultrasonic exfoliation. Taking advantage of the strong interaction between PI chains and MXene nanosheets, the interconnected, highly porous, and hydrophobic PI/MXene aerogels with low density were fabricated, resulting in the improved compressive performance, remarkable oil absorption capacity, and efficient separation of oil and water. For the PI/MXene-3 aerogel (weight ratio, 5.2:1) without any surface modification, the water contact angle was 119° with a density of 23 mg/cm³. This aerogel can completely recover to its original height after 50 compression-release cycles, exhibiting superelasticity and exceptional fatigue-resistant ability. It also showed high absorption capacities to various organic liquids ranging from approximately 18 to 58 times of their own weight. This hybrid aerogel can rapidly separate the chloroform, soybean oil, and liquid paraffin from the water-oil system. The thermally stable hybrid aerogel also exhibited excellent fire safety properties and outstanding reusability under an extreme environment.

Molecular orientation in aligned electrospun polyimide nanofibers by polarized FT-IR spectroscopy

Quantitative explanation on the improved mechanical properties of aligned electrospun polyimide (PI) nanofibers as the increased imidization temperatures is highly required. In this work, polarized FT-IR spectroscopy is applied to solve this problem. Based on the polarized FT-IR spectroscopy and the molecular model in the fibers, the length of the repeat unit of PI molecule, the angle between the fiber axis and the symmetric stretching direction of carbonyl group on the imide ring, and the angle between the PI molecular axis and fiber axis are all investigated. The Mark-Howink equation is used to calculate the number-average molar mass of PI molecules. The orientation states of PI molecules in the electrospun nanofibers are studied from the number-average molar mass of PI molecules and the average fiber diameter. Quantitative analysis of the orientation factor of PI molecules in the electrospun nanofibers is performed by polarized FT-IR spectroscopy.

Graphene Quantum Dot-Aerogel: From Nanoscopic to Macroscopic Fluorescent Materials. Sensing Polyaromatic Compounds in Water

Fluorescence based on quantum confinement is a property restricted to the nanoscopic range. The incorporation of nanoparticles in a three-dimensional polymeric network could afford macroscopic scaffolds that show nanoscopic properties. Moreover, if these scaffolds are based on strong bonds, the stability of the resulting materials can be preserved, thus enhancing their final applications. We report for the first time the preparation of a graphene quantum dot (GQD) composite based on a cationic covalent network. This new material has unusual features: (i) the final composite remains stable after several swelling-deswelling cycles, thus demonstrating strong interactions between GQDs and the polymeric material, and therefore it could be used as a portable system. (ii) Fluorescence emission in the composite and in solution is quasi-independent to the excitation wavelength. (iii) However, and in contrast to the behavior observed in GQD solutions, the fluorescence of the composite remains unaltered over a wide pH range and in the presence of different ions commonly found in tap water. (iv) Fluorescence quenching is only observed as a consequence of molecules that bear aromatic systems, and this could be applied to the preparation of in situ water sensors.

Template-Free Self-Assembly of Fluorine-Free Hydrophobic Polyimide Aerogels with Lotus or Petal Effect

Aerogels have been widely used in the fields like thermal insulation, energy storage, environmental remediation, catalysis, drug release, sensor, and cosmic dust collection, etc. Hydrophobic functionalization not only determines the surface energy and basic physical properties of the target aerogels but also be critical for their long-term stability due to their highly open-porous structures. However, there is still lack of facial and versatile methodologies for the hydrophobic functionalization of aerogels, especially for the nonsilica ones. Herein, two efficient fluorine-free strategies were developed to synthesize various hydrophobic and even superhydrophobic polyimide (PI) aerogels. First, superhydrophobic PI aerogels with contact angle higher than 150° were fabricated by the segregation self-assembly process between poly[4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride)- co- p-phenylene diamine] and poly[biphenyl-3,3',3,4'-tetracarboxylic dianhydride- co-2,2'-dimethylbenzidine] (poly(BPDA-DMBZ)). These PI aerogels exhibited a lotus effect that water droplets could not wet the surface but could easily roll off. Second, various hydrophobic PI aerogels, including the well-documented superhydrophilic PI aerogels derived from DMBZ-BPDA and 4,4'-oxydianiline-BPDA, were synthesized by the density-induced hydrophilicity-hydrophobicity transition approach. These PI aerogels exhibited a petal effect that water droplets on the aerogel surface appeared spherical in shape, which could not roll off even when the aerogel was turned upside down. These two reported strategies might open new and straightforward ways to hydrophobic functionalization of other polymeric aerogel systems.