Ultra-fast heat dissipating aerogels derived from polyaniline anchored cellulose nanofibers as sustainable microwave absorbers

Chitosan-based electroconductive inks without chemical reaction for cost-effective and versatile 3D printing for electromagnetic interference (EMI) shielding and strain-sensing applications

The burgeoning interest in biopolymer 3D printing arises from its capacity to meticulously engineer tailored, intricate structures, driven by the intrinsic benefits of biopolymers-renewability, chemical functionality, and biosafety. Nevertheless, the accessibility of economical and versatile 3D-printable biopolymer-based inks remains highly constrained. This study introduces an electroconductive ink for direct-ink-writing (DIW) 3D printing, distinguished by its straightforward preparation and commendable printability and material properties. The ink relies on chitosan as a binder, carbon fibers (CF) a low-cost electroactive filler, and silk fibroin (SF) a structural stabilizer. Freeform 3D printing manifests designated patterns of electroconductive strips embedded in an elastomer, actualizing effective strain sensors. The ink's high printability is demonstrated by printing complex geometries with porous, hollow, and overhanging structures without chemical or photoinitiated reactions or support baths. The composite is lightweight (density 0.29 ± 0.01 g/cm3), electroconductive (2.64 ± 0.06 S/cm), and inexpensive (20 USD/kg), with tensile strength of 20.77 ± 0.60 MPa and Young's modulus of 3.92 ± 0.06 GPa. 3D-printed structures exhibited outstanding electromagnetic interference (EMI) shielding effectiveness of 30-31 dB, with shielding of >99.9 % incident electromagnetic waves, showcasing significant electronic application potential. Thus, this study presents a novel, easily prepared, and highly effective biopolymer-based ink poised to advance the landscape of 3D printing technologies.

Pickering emulsions as an effective route for the preparation of bioactive composites: A study of nanocellulose/polyaniline particles with immunomodulatory effect

Several studies have reported on application of cellulose particles for stabilizing Pickering emulsions (PE). Here we employ an original approach that involves using these particles as a part of advanced composite colloids made of conducting polymer polyaniline (PANI) and cellulose nanocrystals (CNC) or nanofibrils (CNF). PANI/cellulose particles were prepared using oxidative polymerization of aniline in situ in the presence of CNC or CNF. The type and amount of celluloses (CNC vs CNF) and concentration of precursors (aniline monomer and oxidant) used in the reaction determined properties of the colloidal particles, such as size, morphology and content of PANI. The particles demonstrated intriguing biological characteristics, including no cytotoxicity, antibacterial activity against Staphylococcus aureus and Escherichia coli, antioxidant activity and related immunomodulatory activity. For the first time, such composites were used to successfully stabilize oil-in-water PE with undecane or capric/caprylic triglyceride oils. The properties of the emulsions were determined by the PANI/cellulose particles and oil used. The key finding of the study is the demonstrated ability of PANI/cellulose particles to stabilize PE, as well as the excellent antioxidant activity and ROS scavenging action originating from PANI presence, indicating potential of such systems for use in biomedicine, particularly for wound healing.

Surfactant-Mediated Highly Conductive Cellulosic Inks for High-Resolution 3D Printing of Robust and Structured Electromagnetic Interference Shielding Aerogels

Technological fusion of emerging three-dimensional (3D) printing of aerogels with gel processing enables the fabrication of lightweight and functional materials for diverse applications. However, 3D-printed constructs via direct ink writing for fabricating electrically conductive structured biobased aerogels suffer several limitations, including poor electrical conductivity, inferior mechanical strength, and low printing resolution. This work addresses these limitations via molecular engineering of conductive hydrogels. The hydrogel inks, namely, CNC/PEDOT-DBSA, featured a unique formulation containing well-dispersed cellulose nanocrystal decorated by a poly(3,4-ethylene dioxythiophene) (PEDOT) domain combined with dodecylbenzene sulfonic acid (DBSA). The rheological properties were precisely engineered by manipulating the solid content and the intermolecular interactions among the constituents, resulting in 3D-printed structures with excellent resolution. More importantly, the resultant aerogels following freeze-drying exhibited a high electrical conductivity (110 ± 12 S m-1), outstanding mechanical properties (Young's modulus of 6.98 MPa), and fire-resistance properties. These robust aerogels were employed to address pressing global concerns about electromagnetic pollution with a specific shielding effectiveness of 4983.4 dB cm2 g-1. Importantly, it was shown that the shielding mechanism of the 3D printed aerogels could be manipulated by their geometrical features, unraveling the undeniable role of additive manufacturing in materials design.

Homogeneous wet-spinning construction of skin-core structured PANI/cellulose conductive fibers for gas sensing and e-textile applications

Fiber-based wearable electronic textiles have broad applications, but non-degradable substrates may contribute to electronic waste. The application of cellulose-based composite fibers as e-textiles is hindered by the lack of fast and effective preparation methods. Here, we fabricated polyaniline (PANI)/cellulose fibers (PC) with a unique skin-core structure through a wet-spinning homogeneous blended system. The conductive network formation was enabled at a mere 1 wt% PANI. Notably, PC15 (15 wt% PANI) shows higher electrical conductivity of 21.50 mS cm-1. Further, PC15 exhibits excellent ammonia sensing performance with a sensitivity of 2.49 %/ppm and a low limit of detection (LOD) of 0.6 ppm. Cellulose-based composite fibers in this work demonstrate good gas sensing and anti-static properties as potential devices for smart e-textiles.

Layered polymer composite foams for broadband ultra-low reflectance EMI shielding: a computationally guided fabrication approach

The development of layered polymer composites and foams offers a promising solution for achieving effective electromagnetic interference (EMI) shielding while minimizing secondary electromagnetic pollution. However, the current fabrication process is largely based on trial and error, with limited focus on optimizing geometry and microstructure. This often results in suboptimal electromagnetic wave reflection and the use of unnecessarily thick samples. In this study, an input impedance model was employed to guide the fabrication of layered PVDF composite foams. This approach optimized the void fraction (VF) and the thickness of each layer to achieve broadband low reflection. Moreover, hybrid heterostructures of SiCnw@MXene were incorporated into the PVDF composite foams as an absorption layer, while the conductive PVDF/CNT composite foams served as a shielding layer. Directed by theoretical computations, we found that combining 2.2 mm of PVDF/SiCnw@MXene composite foam (50% VF) and 1.6 mm of PVDF/CNT composite yielded EMI shielding effectiveness of 45 dB, with an average reflectivity (R) of 0.03 and an effective absorption bandwidth of 5.54 GHz (for R < 0.1) over the Ku-band (12.4-18 GHz). Importantly, the corresponding peak R was only 0.000017. Our work showcases a theoretically guided approach for developing absorption-dominant EMI shielding materials with broadband ultra-low reflection, paving the way for cutting-edge applications.

"Three-in-One" Multi-Scale Structural Design of Carbon Fiber-Based Composites for Personal Electromagnetic Protection and Thermal Management

Wearable devices with efficient thermal management and electromagnetic interference (EMI) shielding are highly desirable for improving human comfort and safety. Herein, a multifunctional wearable carbon fibers (CF) @ polyaniline (PANI) / silver nanowires (Ag NWs) composites with a "branch-trunk" interlocked micro/nanostructure were achieved through "three-in-one" multi-scale design. The reasonable assembly of the three kinds of one-dimensional (1D) materials can fully exert their excellent properties i.e., the superior flexibility of CF, the robustness of PANI, and the splendid conductivity of AgNWs. Consequently, the constructed flexible composite demonstrates enhanced mechanical properties with a tensile stress of 1.2 MPa, which was almost 6 times that of the original material. This is mainly attributed to the fact that the PNAI (branch) was firmly attached to the CF (trunk) through polydopamine (PDA), forming a robust interlocked structure. Meanwhile, the composite possesses excellent thermal insulation and heat preservation capacity owing to the synergistically low thermal conductivity and emissivity. More importantly, the conductive path of the composite established by the three 1D materials greatly improved its EMI shielding property and Joule heating performance at low applied voltage. This work paves the way for rational utilization of the intrinsic properties of 1D materials, as well as provides a promising strategy for designing wearable electromagnetic protection and thermal energy management devices.

Cellulose nanocrystalline from biomass wastes: An overview of extraction, functionalization and applications in drug delivery

Cellulose nanocrystals (CNC) have been extensively used in various fields due to their renewability, excellent biocompatibility, large specific surface area, and high tensile strength. Most biomass wastes contain significant amounts of cellulose, which forms the basis of CNC. Biomass wastes are generally made up of agricultural waste, and forest residues, etc. CNC can be produced from biomass wastes by removing the non-cellulosic components through acid hydrolysis, enzymatic hydrolysis, oxidation hydrolysis, and other mechanical methods. However, biomass wastes are generally disposed of or burned in a random manner, resulting in adverse environmental consequences. Hence, using biomass wastes to develop CNC-based carrier materials is an effective strategy to promote the high value-added application of biomass wastes. This review summarizes the advantages of CNC applications, the extraction process, and recent advances in CNC-based composites, such as aerogels, hydrogels, films, and metal complexes. Furthermore, the drug release characteristics of CNC-based material are discussed in detail. Additionally, we discuss some gaps in our understanding of the current state of knowledge and potential future directions of CNC-based materials.

Recent advance in biomass membranes: Fabrication, functional regulation, and antimicrobial applications

Both inorganic and polymeric membranes have been widely applied for antimicrobial applications. However, these membranes exhibit low biocompatibility, weak biodegradability, and potential toxicity to human being and environment. Biomass materials serve as excellent candidates for fabricating functional membranes to address these problems due to their unique physical, chemical, and biological properties. Here we present recent progress in the fabrication, functional regulation, and antimicrobial applications of various biomass-based membranes. We first introduce the types of biomass membranes and their fabrication methods, including the phase inversion, vacuum filtration, electrospinning, layer-by-layer self-assembly, and coating. Then, the strategies on functional regulation of biomass membranes by adding 0D, 1D, and 2D nanomaterials are presented and analyzed. In addition, antibacterial, antifungal, and antiviral applications of biomass-based functional membranes are summarized. Finally, potential development aspects of biomass membranes are discussed and prospected. This comprehensive review is valuable for guiding the design, synthesis, structural/functional tailoring, and sustainable utilization of biomass membranes.

Sustainable cellulose-based multifunctional material for electromagnetic shielding, flame retardancy and antibacterial

Biomass-based multifunctional electromagnetic shielding materials have attracted extensive interest in academia and industry due to the sustainability of biomass and the environmental adaptability of multifunctional materials. After removing lignin and hemicellulose wood become a porous substrate with aligned cellulose, which is a good platform for building cellulose-based materials. In this work, a cellulose composite with sandwich-like structure was constructed by in-situ polymerization of aniline on delignified wood and coating a PDMS/CNT layer. Benefiting from the natural porous hierarchical structure and the constructed multilayer continuous conductive network, the PDMS/CNT/PANI WA exhibits excellent electrical conductivity (18.6 S/m) and electromagnetic shielding performance (shielding efficiency value of 26 dB at the X band (8.2-12.4 GHz)). The synergistic effect of PANI and CNT endowed the material with excellent flame retardancy (HRR, THR and HRC decreased by 84 %, 53.4 % and 83.3 %) and significant antibacterial activity. Moreover, PDMS imparts a water contact angle of 105° to the material, which acts as a protective layer, further improves the durability of the material. This work provides a new strategy for developing sustainable and multifunctional electromagnetic shielding materials.

Ultralight and Highly Conductive Silver Nanowire Aerogels for High-Performance Electromagnetic Interference Shielding

Metal-based materials possess superior electromagnetic interference (EMI) shielding performance because of their extraordinary electrical conductivity. Nevertheless, the high density and structural rigidity of metals seriously limit their applicability in portable and wearable electronic equipment. A common method for reducing the density of metal-based materials is to prepare metal nanowire aerogels by freeze-drying, but the weak connection among the nanowires results in poor mechanical and electrical properties. Herein, a facile approach is developed for the one-step synthesis of silver nanowire (AgNW) aerogels with ultralow density, good flexibility, high electrical conductivity, and a robust structure. The gel is directly formed by in situ assembly of AgNWs. The end-to-end nanojoining of AgNWs contributes to constructing an interconnected three-dimensional (3D) network, resulting in improved mechanical and electrical properties. The AgNW aerogel with an ultralow density of 4.87 mg cm^-3 demonstrates a high electrical conductivity of 4584 S m^-1. Moreover, the porous structure of the AgNW aerogel provides numerous interfaces for multiple reflections and scattering of EM waves, allowing them to be continuously absorbed and dissipated within the aerogel. Thus, the AgNW aerogel exhibits a superb EMI shielding effectiveness (SE) of 109.3 dB and a normalized surface specific SE (SSE/t, calculated as the SE divided by the density and thickness) of 353 183 dB cm² g^-1, significantly above that of previously known shielding materials. This work provides a new route for preparing high-performance metal nanowire aerogels and their great potential in EMI shielding.

High-Performance and Rapid-Response Electrical Heaters Derived from Cellulose Nanofiber/Silver Nanowire Nanopapers for Portable Thermal Management

High-performance electrical heaters with outstanding flexibility, superior portability, and mechanical properties are highly desirable for portable thermal management. However, it is still a huge challenge to simultaneously achieve competent electrical heating performances and excellent mechanical properties. Herein, inspired by the Janus structure, versatile electrical heaters are developed via a sequential assembly followed by a hot-pressing strategy. The elaborately designed Janus structure is composed of a nanofibrillated cellulose (NFC) layer and a partially wrapped silver nanowire (AgNW) skeleton in the NFC substrate. Owing to the perfect introduction of nano-soldered points induced by thermal welding decoration, the resultant NFC/AgNW papers (NAPs) possess great flexibility, excellent mechanical strength (176.75 MPa), extremely low sheet resistance (0.60 Ω/sq), and superior electrical stabilities against mechanical deformations. Moreover, benefitting from these fascinating attributes, the NAP-based electrical heaters exhibit a remarkable heating temperature (∼220 °C), ultrafast electro-thermal response (<10 s), and groundbreaking long-term stability (∼105 °C for >186 h) and repeatability (>20,000 cycles) with low AgNW contents and driving voltages (0.5-5.0 V), which far surpass those of the previously reported and conventional indium tin oxide-based Joule heaters. Impressively, large-area production feasibilities of NAPs are demonstrated and assembled into multifunctional applications, including personal thermal management, healthcare thermotherapy, multifunctional cups, and smart homes, indicating their promising potential for wearable devices, artificial intelligence, and specific heating systems in the fields of aerospace, military, and intelligent life.

Recent Progress in Electromagnetic Interference Shielding Performance of Porous Polymer Nanocomposites—A Review

The urge to develop high-speed data transfer technologies for futuristic electronic and communication devices has led to more incidents of serious electromagnetic interference and pollution. Over the past decade, there has been burgeoning research interests to design and fabricate high-performance porous EM shields to tackle this undesired phenomenon. Polymer nanocomposite foams and aerogels offer robust, flexible and lightweight architectures with tunable microwave absorption properties and are foreseen as potential candidates to mitigate electromagnetic pollution. This review covers various strategies adopted to fabricate 3D porous nanocomposites using conductive nanoinclusions with suitable polymer matrices, such as elastomers, thermoplastics, bioplastics, conducting polymers, polyurethanes, polyimides and nanocellulose. Special emphasis has been placed on novel 2D materials such as MXenes, that are envisaged to be the future of microwave-absorbing materials for next-generation electronic devices. Strategies to achieve an ultra-low percolation threshold using environmentally benign and facile processing techniques have been discussed in detail.

Integration of efficient microwave absorption and shielding in a multistage composite foam with progressive conductivity modular design

Ultra-efficient electromagnetic interference (EMI) shielding composites with excellent microwave absorbing properties are the most desirable solution for eliminating microwave pollution. However, integrating absorbing and electromagnetic shielding materials is a difficult challenge because they have different design strategies. In this work, the compatibility of high absorption and shielding capability based on progressive conductivity modular design was realized. Reduced graphene oxide@ferroferric oxide/carbon nanotube/tetraneedle-like ZnO whisker@silver/waterborne polyurethane (rGO@Fe₃O₄/CNT/T-ZnO@Ag/WPU) multistage composite foams with aligned porous structures were fabricated, which exhibited an excellent average EMI SE > 92.3 dB and remarkable microwave absorption performance with reflection loss < -10 dB in the frequency range of 8.2-18.0 GHz. The average shielding effectiveness of reflection (SE_R) and reflectivity (R) are as low as 0.065 dB and 0.015, respectively. Besides, the correlations between the morphology and structure of the composite foam and the electromagnetic wave attenuation mechanism were established via electromagnetic simulation. Significantly, the integration of efficient absorbing and shielding materials was realized for the first time. Such composite foams with electromagnetic wave absorption and shielding characteristics are light weight and structurally designable with an adjustable shielding mechanism, and exhibit low filler consumption and high performance. They display promising applications in demanding electromagnetic environments. Our work provides a new strategy to design ultra-efficient EMI shielding materials with reliable absorption-dominated features.

Polydopamine Induced Wettability Switching of Cellulose Nanofibers/n-Dodecanethiol Composite Aerogels

The novel wettability switchable cellulose nanofiber- (CNF-) based aerogel was conveniently prepared by polydopamine mediated composition of CNF and n-dodecanethiol. The wettability of aerogels can be controlled by adjusting the PDA and n-dodecanethiol loading content, which leads to a variation of water contact angle from 0-149°. The PDA was coated on cellulose nanofibers via hydrogen bonds and then n-dodecanethiol was anchored onto the scaffolds by Michael addition reaction, which was revealed by XPS and FTIR spectra. The composite aerogel can selectively absorb a series of oily liquids from the oil/water mixture, with the maximum absorption capacity of 68 g/g. This work presented a facile strategy to prepare wettability switchable CNF-based heterogenous aerogel and exhibited the potential of the composite aerogel for oil/water separation.

Facile Preparation and Characteristic Analysis of Sulfated Cellulose Nanofibril via the Pretreatment of Sulfamic Acid-Glycerol Based Deep Eutectic Solvents

A deep eutectic solvent (DES) composed of sulfamic acid and glycerol allowed for the sustainable preparation of cellulose nanofibrils (CNF) with simultaneous sulfation. The reaction time and the levels of sulfamic acid demonstrated that fibers could be swelled and sulfated simultaneously by a sulfamic acid-glycerol-based DES and swelling also promoted sulfation with a high degree of substitution (0.12). The DES-pretreated fibers were further nanofibrillated by a grinder producing CNF with diameters from 10 nm to 25 nm. The crystallinity ranged from 53–62%, and CNF maintained the original crystal structure. DES pretreatment facilitated cellulose nano-fibrillation and reduced the energy consumption with a maximum reduction of 35%. The films prepared from polyvinyl alcohol (PVA) and CNF showed good UV resistance ability and mechanical properties. This facile and efficient method provided a more sustainable strategy for the swelling, functionalization and nano-fibrillation of cellulose, expanding its application to UV-blocking materials and related fields.

Genetic Algorithms to Automate the Design of Metasurfaces for Absorption Bandwidth Broadening

In this paper, we present a method to automate the design of an efficient metasurface, which widens the bandwidth of the substrate. This strategy maximizes the potential of the substrate for the application of broad-band absorption. The design is achieved by utilizing the coding metasurface and a combination of two types of intelligent algorithms. First, inspired by the coding metasurface, a large number of structures are generated to act as potential metasurface unit patterns by randomly generating the associated binary codes. Then, the binary codes are directly substituted as optimization objects into a genetic algorithm to find the optimal metasurface. Finally, a neural network is introduced to replace the finite element analysis method to correlate the binary codes with the absorbing bandwidth. With the participation of neural networks, the genetic algorithm can find the optimal solution in a considerably short time. This method bypassed the prerequisite physical knowledge required in the process of metasurface design, which can be used for reference in other applications of the metasurface.

Study of the effect of band gap and photoluminescence on biological properties of polyaniline/CdS QD nanocomposites based on natural polymer

In this work, band gap, photoluminescence and biological properties of new bionanocomposites based on polyaniline (PANi)/hydrolyzed pectin (HPEc)/cadmium sulfide (CdS) QD nanoparticles (NPs) were studied. In order to improve the morphology and properties, CdS NPs were modified with epichlorohydrin to obtain the modified CdS (mCdS). The CdS@HPEc-g-PANi and mCdS@HPEc-g-PANi samples were synthesized via heterogeneous chemical polymerization and characterized by FTIR, ¹HNMR, SEM/XRD, EDX/TEM/EDX-mapping and TGA analyses. The objective of this work is the study of physical, optical and cytotoxicity properties of the nanocomposites and comparison between them. The SEM, XRD and TGA images showed that the modification of NPs resulted in homogeneous morphology, increase of crystalline structure and high thermal stability which influenced on physical and biological property. According to UV-DRS analysis, the mCdS@HPEc-g-PANi indicated lower energy gap compared to the CdS@HPEc-g-PANi nancomposite. The presence of conductive polymer and synergy effect between the PANi and CdS caused higher PL intensity in the CdS@HPEc-g-PANi nanocomposite compared to pure CdS. The emission intensity in the mCdS@HPEc-g-PANi nanocomposite was reduced since the organic modifying agent cause reducing emission intensity. The mCdS@HPEc-g-PANi nanocomposite, due to more compatibility of organic agent with cellular walls of biological cells that help to the diffusion of metal CdS NPs into cell tissue indicated more toxicity effect on cell growth.