Tough Films Research Articles

Preparation of porous silicon/metal composite negative electrode materials and their application in high-energy lithium batteries

Abstract Porous silicon/metal composites have huge specific surface area, rich pore structure, tough framework system and low SEI film formation rate, and have great application prospects in the field of high-energy lithium batteries. Porous silicon/metal composites have abundant pore structure, which can greatly alleviate the volume effect of silicon during charging and discharging. The introduction of metal can increase the conduction rate and reduce the formation rate of SEI film. However, the development of a facile and rapid method to synthesize porous silicon/metal composites remains a challenge for current research. Based on the current research progress of porous silicon/metal composites and related literatures, in this paper, the preparation methods of porous silicon/metal composites in recent years are reviewed in detail, with a focus on their applications in the field of high-energy lithium batteries. Finally, the future development direction of porous silicon/metal composites is further prospected.

Fluorescence-color-changing biomimetic tough films with simultaneous shape-deformation triggered by pH

Stimuli-responsive materials with complex practical functions that could imitate certain behaviors of living organisms have wide potential applications in frontier fields. However, the fabrication of stimuli-responsive films with simultaneous change in fluorescence color and shape in response to a single stimulus, especially by a simple fabrication strategy, remains a challenge. Herein, a simple hydrogel-film-post crosslinking strategy is proposed to prepare films that exhibit fluorescence change accompanying with shape deformation under pH stimulus. The synchronous changes are realized by the combination of dynamic boron chemistry and pH-sensitive lanthanide complexes. Under different pH conditions, the protonation/deprotonation of the ligands coordinated to Eu3+ ions could generate switchable on/off fluorescence behavior, while the association/dissociation of borate ester bonds between 3-aminobenzeneboronic acid (SA-PBA) and polyvinyl alcohol (PVA) could lead to macroscopic deformation. The existence of borate ester bonds is beneficial to the mechanical properties of composite films. Under pH stimulus, the film-based artificial flower could simulate the flowering of natural flowers accompanying with color changes and the film-based gripper could grasp object with a visual signal, which demonstrates that the SA-PBA/PVA/EuL films have great potential for wide application.

Synthesis and characterization of new aromatic copoly(ether amide)s bearing 4-trifluoromethylphenyl-2,6-diphenylpyridyl moieties in the main chain

A series of new aromatic fluorinated copoly(ether amide)s containing 4-(4-trifluoromethylphenyl)-2,6-diphenylpyridyl moiety with high molecular weight were prepared by a low-temperature solution polycondensation of terephthaloyl chloride with 4-(4-trifluoromethylphenyl)-2,6-bis(4-aminophenyl)pyridine and 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene with various mole ratios of the two monomers ranged from 20/80 to 80/20. All polymers were amorphous and soluble in common organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide and tetrahydrofuran at room temperature or upon heating at 70oC, and could be solution cast into transparent, tough, and flexible films with tensile strengths of 66.9–80.2 MPa, tensile moduli of 1.84–2.03 GPa, and elongations at break of 11.8–20.7%. These new polyamides displayed good thermal stability with gradually increasing of glass temperatures of 259–285oC as an increase of the 4-(4-trifluoromethylphenyl)-2,6-diphenylpyridyl component, the temperature at 10% weight loss of 476–505oC, and the residue of 55–61% at 750oC in nitrogen. They also exhibited low dielectric constants of 3.11–3.38 (1 MHz), low moisture absorption in the range of 1.43–1.75%, and high transparency with an UV–vis absorption cut-off wavelength in the 350–368 nm range.

Green polymer synthesis and low dielectric properties obtained by oxidative polymerization of thymol with CuCl-2-(p-tolyl)pyridine catalyst

Polymerization of thymol (2-isopropyl-5-methylphenol) was conducted using a bulky copper catalyst (CuCl-2-(p-tolyl)pyridine) in toluene under dioxygen atmosphere to give the corresponding 1,4-coupled polythymol (PPETh) with the Mn up to 22.7 kDa in moderate yield. The OH absorption in the IR spectrum disappeared almost completely and the presence of only nine signals in the 13C NMR spectrum clearly indicated the satisfactory formation of the expected linear PPETh. The PPETh exhibited good solubility in tetrahydrofuran, N,N-dimethylformamide, 1,4-dioxane, and CHCl3 (well-known for preparing industrial PPE26 from oxidative polymerization of 2,6-dimethylphenol), and good thermostability (Td5 in N2 of 410 °C). PPETh was mixed with PPE26 and the tough films were successfully prepared by the hot-press method in the weight fraction of PPETh up to 60%. TMA and DMA were performed to evaluate the Tg and the CTE of the films at 179–222 °C and 82–130 ppm/K, respectively. The dielectric properties were measured using a cavity resonator, in which the relative permittivity ranged from 2.28 (PPETh60%) to 2.46 (PPE26), and the dissipation factor from 0.00173 (PPE26) to 0.00495 (PPETh60%) at 10 GHz. The bulky isopropyl substituent gave to the PPETh polymer good solubility and insulating property with maintained thermal stability.

Soluble, transparent and heat-resistant fluorinated copoly(ether imide)s containing pyridyl and biphenyl units in the main chain

A series of new fluorinated copoly(ether imide)s containing pyridyl and biphenyl moieties were prepared by thermal imidization of poly(amic acid)s derived from 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (BATB), 4-(4-trifluoromethylphenyl)-2,6-bis(4-aminophenyl)pyridine (TFMPBPP) and 3,3’,4,4’-biphenyltetracarboxylic dianhydride with various mole ratios of BATB and TFMPBPP ranging from 80/20 to 20/80. All copoly(ether imide)s were amorphous and soluble in polar solvents such as N,N-dimethylacetamide and N-methyl-2-pyrrolidone at room temperature or upon heating at 70 °C, and displayed good thermal properties with gradually increasing of a glass transition temperature ranged from 282 to 347 °C as an increase of the TFMPBPP component, the temperature at 5% weight loss of 574–586 °C, and the residue of 57–62% at 750 °C in nitrogen. Tough and flexible polymer films also exhibited outstanding mechanical properties with tensile strengths of 109.1–111.9 MPa, tensile moduli of 1.3–1.5 GPa, and elongations at break of 27.9–48.7%, low dielectric constants of 2.98–3.15 (1 MHz) and water uptake 0.36–0.55%, as well as high optical transparency with the UV-vis cutoff wavelength in the 370–382 nm range and the wavelength of 80% transparency in the range 518–550 nm.

Bridging MXene layers for strong multifunctional films

In a recent work in Science, Cheng’s group at Beihang University demonstrated strong and tough MXene films with excellent conductivity, environmental stability, and electromagnetic interference shielding. Sequential bridging of 2D MXene sheets with sodium carboxymethyl cellulose and borate ions produced multifunctional composites. In a recent work in Science, Cheng’s group at Beihang University demonstrated strong and tough MXene films with excellent conductivity, environmental stability, and electromagnetic interference shielding. Sequential bridging of 2D MXene sheets with sodium carboxymethyl cellulose and borate ions produced multifunctional composites.

Strong, tough and degradable cellulose nanofibers-based composite film by the dual crosslinking of polydopamine and iron ions

It is urgently needed to develop an eco-friendly composite films with excellent mechanical properties for biomedicine, optoelectronics, and water treatment applications. Here, we acquired a strong, tough, and sustainable TEMPO-oxidized cellulose nanofiber (TOCN)-based composite film by the dual crosslinking of polydopamine (PDA) and iron ions (Fe3+). The ultimate TOCN/PDA/Fe3+ ternary composites exhibited outstanding mechanical properties with a strength of 220 MPa, a strain of 13.26% and a toughness of 17.73 MJ m−3, increasing by 113%, 149%, and 417% compared to pure TOCN film, respectively. This result was caused by the coordination bonds and covalent bonds. Moreover, the TOCN/PDA/Fe3+ composite film also showed excellent degradability, thermal stability and UV-shielding capability.

Acacia mangium tannin functionalized graphene nanoplatelets produced via ball-milling for sustainable soy protein-based film

A simple and green natural spider silk inspired strategy is proposed for fabricating advanced soy protein (SP)-based film by introducing Acacia mangium tannin (AMT) functionalized graphene nanoplatelets (AMT-GnPs), greenly and cost-effectively produced via ball milling graphite with AMT. The prepared film, namely SPEI/GnPs, exhibited noticeable improvement in mechanical properties over the neat SP-based film such as tensile strength (11.60 vs. 2.19 MPa) and toughness (21.12 vs. 3.09 MJ m-3). In addition, such developed biomimetic film still exhibited a high strain at failure (220.3%). The outstanding performance was attributable to the formation of dense interfacial covalent and H-bonding interactions between the scattered AMT-GnPs and the protein matrix. Moreover, after incorporating AMT-GnPs, the SPEI/GnPs film featured excellent UV-blocking performance and good water resistance. Overall, this study offers a facile biomimetic strategy for strong, tough, and biodegradable films for many potential applications like packaging and UV-blocking bioproducts.

Synthesis and properties of low dielectric constant phenolphthalein-based poly (aryl ether) resin containing isopropyl groups

In this study, a novel phenolphthalein poly (ether nitrile) containing isopropyl groups (iPrPENC) was successfully synthesized via SN2 aromatic nucleophilic polycondensation. The flexible and tough iPrPENC films exhibited an intrinsic low dielectric constant value of 2.86 at the frequency of 1 MHz. The resin has good thermal stability and mechanical property. In addition, it can be dissolved in common organic solvents. Thus, the functional poly (aryl ether nitrile) possessed attractive potential applications in the field of high-performance flexible electronic packaging materials.

Highly Refractive Polyimides Derived from Efficient Catalyst-Free Thiol–Yne Click Polymerization

Polyimides (PIs), owing to their inherent high refractive index and excellent physical properties, are required in advanced optical applications. They are traditionally synthesized through conventional two-step polycondensation, followed by high-temperature or chemical imidization, inevitably increasing energy consumption, environmental pollution, and production duration. Herein, for the first time, we synthesized PIs consisting of vinylene sulfide linkages via an efficient catalyst-free thiol–yne click polymerization, which would be accomplished within 2 h at 25 °C by simply mixing the dithiols and bisimide-containing diynes in THF, affording PIs with tensile strength ranging from 106.3 to 114.9 MPa, glass transition temperature up to 238 °C, thermal decomposition temperature as high as 381 °C, and desirable solubility, so that it was easily cast from solution into tough films. Moreover, the BPADA-TBT PI film demonstrates good optical performance, with its refractive index exceeding 1.70 at 633 nm and transmittance above 81% at 450 nm, making it a potential candidate in advanced optical applications.

Tough and Biodegradable Gelatin-Based Film via the Synergistic Effect of Multi-Cross-Linking

Tough and Biodegradable Gelatin-Based Film via the Synergistic Effect of Multi-Cross-Linking

Modulation of interfacial interactions toward strong and tough cellulose nanofiber-based transparent thin films with antifogging feature

Cross-linking is often performed to overcome the weak mechanical properties of native polymer films in order to expand their functional properties and applications. While this approach offers enhanced strength to the film, the film also suffers from low flexibility, low toughness and high brittleness. However, in view of the growing demand for strong and tough transparent thin films, this article reported our study to develop films made from cellulose nanofiber (CNF) via tailoring the interfacial bonding interactions through the application of glycerol (Gly) and glutaraldehyde (GA), which functioned as a plasticizer and cross-linking agent, respectively. Among the prepared films, the 10GA-8Gly-CNF film exhibited the best results with regard to the enhancement in the tensile strength (21.1%), Young's modulus (10.6%), elongation at break (100%) and toughness (32.7%), as compared to the native CNF film. Importantly, treating the surface of the film to radiofrequency oxygen plasma endowed the film with antifogging property, without compromising the optical clarity.

Tough and strong biomimetic soy protein films with excellent UV-shielding performance

To develop strong and tough bio-based composite films as replacements for synthetic polymer films is challenging. Based on the strong adhesion of the comb-like structure of geckos’ feet or pressure-sensitive resins on substrates, a comb-like polymer-aminated dialdehyde starch (A-DAS) was designed and prepared from polyamide polyamine polymer and dialdehyde starch via a Schiff-based reaction, and then combined with soy protein isolate (SPI) to develop a protein-based film. The comb-like A-DAS exhibited strong adhesion with SPI molecules by forming multiple hydrogen bonds, which created a noncovalent network that improved both the strength and toughness of the resultant film. The results showed that after integrating A-DAS (SPI:A-DAS weight ratio of 2:1), the tensile strength of the film dramatically increased by 1072.2% to 25.09 MPa, which is markedly better than that of other reported protein-based films. The toughness of the SPI/A-DAS film increased to 16.74 MJ/m 3 . Notably, the modified film could block 100% of the ultraviolet transmittance (<400 nm) owing to the imine group in A-DAS. This strategy offers a simple and effective way to construct strong and tough composite materials with ultraviolet-barrier performance, indicating potential applications in tissue engineering, hydrogels, and coating modification. • A high-performance SPI-based film was prepared inspired by gecko feet and PSAs. • Strong hydrogen bonds promoted the toughness of the SPI-based film. • The tensile strength and toughness of the films improved by 1072.2% and 307.3%. • The SPI-based film exhibited UV-shielding properties for packaging.

Synthesis of tetraazacalix[2]arene[2]triazine-containing poly(dimethylsiloxane) with elastic property induced by pinning effect of the calixarene ring

Tetraazacalix[2]arene[2]triazine dichloride was polymerized with telechelic poly(dimethylsiloxane)s having NH2 terminals (PDMSx; degree of polymerization x = 8, 18, 38) via solution polycondensation to give the corresponding azacalixarene-containing polymers (ACAT-PDMSx) in good yield. The fraction of the hard ACAT moiety (fHS) of the ACAT-PDMS polymers was calculated to be 33.0%, 20.4%, and 11.6% for x of 8, 18, and 38, respectively. The number-average molecular weight (Mn) of the polymers ranged from 20 to 32 kDa, and freestanding tough films were successfully fabricated via solvent cast method. As a control sample, a polymer not containing azacalixarene (AnDCT-PDMS) with Mn and fHS values of 21 kDa and 19.8%, respectively, was prepared via the solution polymerization of 2-anilino-4,6-dichloro-1,3,5-triazine (AnDCT) with PDMS8. Although the fHS values of AnDCT-PDMS8 and ACAT-PDMS18 were similar, the film obtained from the former polymer was much softer and sticky at room temperature than that from the latter. Interestingly, the ACAT-PDMS18 film exhibited a tensile strength of 2.7 MPa, a modulus of 2.0 MPa, and an elongation at break of 200%. The glass transition temperature of the ACAT-PDMSx films ranged from 77 °C to 105 °C according to thermomechanical and dynamic mechanical analyses. Wide-angle X-ray diffraction and polarized optical microscopy studies indicated that the azacalixarene units were first locally aggregated via multiple hydrogen bonds within the ACAT-PDMSx films and then were well dispersed in the film on heating. The ACAT-PDMS polymer showed no cytotoxicity to HeLa and IMR-90 cells in the experimental concentration of below 100 μg/mL.

Extremely strong and tough chitosan films mediated by unique hydrated chitosan crystal structures

Chitosan-based materials have attracted considerable attention owing to their inherent biodegradability, biocompatibility, and antimicrobial properties. However, the establishment of a scalable technology for the fabrication of high-strength and high-toughness chitosan films remains a major challenge. Herein, a new route for the fabrication of high-strength and high-toughness chitosan films mediated by a unique hydrated chitosan crystal structure is reported, using an aqueous KOH/urea solution as a solvent and an aqueous KCl solution as a neutralization bath. The KCl concentration, neutralization temperature, and neutralization time significantly affect the self-assembly and lateral aggregation of chitosan chains and the microstructure and morphology of the chitosan hydrogels and films. Furthermore, stretching orientation endows the chitosan films with a high tensile strength, Young’s modulus, and work of fracture of 579 ± 52 MPa, 18.8 ± 1.5 GPa, and 26.7 ± 6.9 MJ m−3, respectively. To the best of our knowledge, the chitosan films developed in this study are the first example of extremely high-strength and high-toughness chitosan films. We believe that our findings will be useful for the fabrication of polysaccharide-based films with excellent mechanical properties and in broader applications in the fields of biomedicine, flexible bioelectronics, water treatment, and food packaging.

High-tensile regenerated cellulose films enabled by unexpected enhancement of cellulose dissolution in cryogenic aqueous phosphoric acid

We have demonstrated, for the first time, high-efficient non-destructive and non-derivative dissolution of cellulose could be achieved in cryogenic aqueous phosphoric acid. Cellulose from different sources and of varying degree of polymerization from 200 (MCC) to 2200 (cotton fabric) could be dissolved completely to afford solutions containing 5 wt%–18 wt% cellulose, from which ultra-strong and tough cellulose films of tensile strength as high as 707 MPa could be obtained using water as the coagulant. These solutions can be stored at −18 °C for extended time without noticeable degradation while desired degree of polymerization is also attainable by tuning the storage conditions. The findings of this work call for renewal attention on phosphoric acid as a promising cellulose solvent for being non-toxic, non-volatile, easy to handle, and cost-effective.

Ultrathin and Highly Tough Hydrogel Films for Multifunctional Strain Sensors.

With good flexibility and biocompatibility, hydrogel-based sensors have been widely used in human motion detection, artificial intelligence, human-machine interface, and other fields. Previous research on hydrogel-based sensors has focused on improving the mechanical properties and signal transmission sensitivity. With the development of human smart devices, there is an increasing demand for hydrogel sensor comfort and more application functions, such as ultrathin structures and recognition functions for contact surfaces, which are realized with higher requirements for the thickness, flexibility, friction resistance, and biocompatibility of hydrogels. Inspired by the ultrathin and flexible characteristics of human organ biofilms, we constructed conductive hydrogel films by using the flim-casting and glycerol-H2O secondary hydration methods. This ultrathin structure enables the hydrogel films to have a high elongation at break of 523.3%, a stress of 3.5 MPa, and a good friction resistance. Combined with the excellent sensing properties (gauge factor = 2.1 and a response time of 200 ms), the hydrogel film-based sensor can not only record human motion signals but also recognize the surface texture and roughness of objects, such as glass, brushes, wood, and sandpaper with mesh sizes of 80, 50, and 24, accurately. In addition, this hydrogel film has a series of excellent properties such as UV shielding, antiswelling ability, and good biocompatibility. This research provides a novel way for the development of emerging soft-material smart devices, such as hydrogel-based electronic skin and soft robots.

The tough, fluorescent and adhesive elastomer in aqueous dispersion: The contribution of aromatic amide-urea segments

The recent researches on waterborne polyurethane (WPU) have been much highlighted to fulfill the both requirements of environment and material performance. Herein, a simple copolymerization approach is demonstrated toward the tough, fluorescent and adhesive WPU elastomer films by the incorporation of para aromatic amide (aramid)-urea segments in the backbone of the polymer. The synthesis of the poly(amide-urea-urethane) was carried out through two steps of chain extension reactions, and the aramid motif, 4,4'-diaminobenzanilide (DABA) was used as the chain extender in the second step of chain extension before the polymer was neutralized and dispersed in water. The aramid-urea segments promoted the H-bonding association of the polyurethane matrix during the film formation of the WPU, which facilitated the microphase separation as well as the pronounced elevation of film performance. Under the DABA content of 4 wt%, the ultimate tensile strength increased to 73 MPa, 380% of that without DABA incorporation. Importantly, the WPU film showed remarkable toughness of 372 MJ·m-3 with the elongation at break of ~1250%. The water adsorption of the film was also suppressed to below 3% in 24 h of the water uptake test. Not only that, but the elastomer film also exhibited high adhesion to metal surfaces to withstand a hanging weight of 27.5 kg with the bonding area of 25 mm × 50 mm. Besides, the film was also able to emit bright blue fluorescence under the excitation of UV light. The combining of high strength, toughness, water resistance and photoluminescence in the WPU will provide the elastomer great potential as environmentally friendly multifunctional material.

Structure reorganization of cellulose hydrogel by green solvent exchange for potential plastic replacement

Petroleum-based plastics have raised great environmental concerns from the beginning of their production to the end-of-life cycle. It is urgently needed to develop sustainable and green materials with certain plastic properties. Herein, biobased cellulose films are fabricated from low quality cotton cellulose by manipulating its hydrogen bonding network with green solvents. The cellulose is dispersed in inorganic salts (ZnCl2/CaCl2) to form ionic hydrogels, and then transformed into tough and flexible films through ethanol exchange and air drying. Without extra hot-pressing treatment, the aggregate structure of cellulose is re-organized with the disruption and re-construction of hydrogen bonds. Benefiting from the densely packed structure and highly in-plane orientation, the cellulose film presents outstanding optical, thermal and mechanical properties. Such cellulose materials hold a potential for plastic replacement in the field of biodegradable packing.

Engineering Tough Metallosupramolecular Hydrogel Films with Kirigami Structures for Compliant Soft Electronics.

A simple and effective approach is demonstrated to fabricate tough metallosupramolecular hydrogel films of poly(acrylic acid) by one-pot photopolymerization of the precursor solution in the presence of Zr4+ ions that form coordination complexes with the carboxyl groups and serve as the physical crosslinks of the matrix. Both as-prepared and equilibrated hydrogel films are transparent, tough, and stable over a wide range of temperature, ionic strength, and pH. The thickness of the films can be easily tailored with minimum value of ≈7 μm. Owing to the fast polymerization and gelation process, kirigami structures can be facilely encoded to the gel films by photolithographic polymerization, affording versatile functions such as additional stretchability and better compliance of the planar films to encapsulate objects with sophisticated geometries that are important for the design of soft electronics. By stencil printing of liquid metal on the hydrogel film with a kirigami structure, the integrated soft electronics shows good compliance to cover curved surfaces and high sensitivity to monitor human motions. Furthermore, this strategy is applied to diverse natural and synthetic macromolecules containing carboxyl groups to develop tough hydrogel films, which will open opportunities for the applications of hydrogel films in biomedical and engineering fields.