Environmentally stable, photochromic and thermotropic organohydrogels for low cost on-demand optical devices

Photochromic Film Based on a Mixed-Heteroatom-Templated ErIII-Incorporated Polyoxometalate Used for Inkless Prints and Anti-Counterfeiting

Photochromic films have attracted increasing attention for their potential in information storage and photoswitchable devices. Developing novel photochromic materials is still a highly challenging topic. In this work, we successfully obtained an unprecedented mixed-heteroatom-templated ErIII-incorporated polyoxometalate [H2N(CH3)2]18Na2K2H12{Er2(H2O)10W14O43[SeTeW15O54][B-α-TeW9O33]2}2·117H2O (1) by concurrently introducing the [TeO3]2- and [SeO3]2- heteroanion templates into the Er3+/WO42- system. The most attractive feature is that this polyoxoanion of 1 consists of three kinds of polyoxometalate building units such as classical trivacant Keggin [B-α-TeW9O33]8-, rarely seen trivacant TeIV-SeIV-oriented Dawson-like [SeTeW15O54]10-, and extraordinary [W14O43]2- with an infrequent [WVIO7(WVI5O20)]18- pentagon subunit. Based on the photochromism feature of polyoxometalates in the presence of organic electron donors under light irradiation, a photochromic composite film GEL/TEG/1 was fabricated by mixing 1 with gelatin (GEL) and triethylene glycol (TEG). The GEL/TEG/1 film shows good photochromic properties under 365 nm UV irradiation. The film changed color within 15 min under UV irradiation. The photochromic properties endow the film with fast and easy "'printing'" performance. The "printed" text or pattern in the film can be erased within 35 h in an atmospheric environment at room temperature, or colored film can be quickly erased within 3 h at 60 °C and the film can be reused for printing again. Moreover, the coloration and decoloration process can be repeated for at least 10 cycles, indicating that the GEL/TEG/1 film possesses favorable cycle performance. Further, the GEL/TEG/1 film can be used for ink-free printing and anti-counterfeiting encryption. This work not only offers a workable method for constructing mixed-heteroatom-templated polyoxometalates containing different kinds of uncommon building units but also offers some significant insights into the photochromic potential applications of polyoxometalate-based materials.

Polyacrylamide/sodium alginate/sodium chloride photochromic hydrogel with high conductivity, anti-freezing property and fast response for information storage and electronic skin

Photochromic hydrogels have promising prospects in areas such as wearable device, information encryption technology, optoelectronic display technology, and electronic skin. However, there are strict requirements for the properties of photochromic hydrogels in practical engineering applications, especially in some extreme application environments. The preparation of photochromic hydrogels with high transparency, high toughness, fast response, colour reversibility, excellent electrical conductivity, and anti-freezing property remains a challenge. In this study, a novel photochromic hydrogel (PAAm/SA/NaCl-Mo7) was prepared by loading ammonium molybdate (Mo7) and sodium chloride (NaCl) into a dual-network hydrogel of polyacrylamide (PAAm) and sodium alginate (SA) using a simple one-pot method. PAAm/SA/NaCl-Mo7 hydrogel has excellent conductivity (175.9 S/cm), water retention capacity and anti-freezing properties, which can work normally at a low temperature of -28.4 °C. In addition, the prepared PAAm/SA/NaCl-Mo7 hydrogel exhibits fast response (<15 s), high transparency (>70 %), good toughness (maximum elongation up to 1500 %), good cyclic compression properties at high compressive strains (60 %), good biocompatibility (78.5 %), stable reversible discolouration and excellent sensing properties, which can be used for photoelectric display, information storage and motion monitoring. This work provides a new inspiration for the development of flexible electronic skin devices.

Coaxial 3D Bioprinting Process Research and Performance Tests on Vascular Scaffolds

Three-dimensionally printed vascularized tissue, which is suitable for treating human cardiovascular diseases, should possess excellent biocompatibility, mechanical performance, and the structure of complex vascular networks. In this paper, we propose a method for fabricating vascularized tissue based on coaxial 3D bioprinting technology combined with the mold method. Sodium alginate (SA) solution was chosen as the bioink material, while the cross-linking agent was a calcium chloride (CaCl2) solution. To obtain the optimal parameters for the fabrication of vascular scaffolds, we first formulated theoretical models of a coaxial jet and a vascular network. Subsequently, we conducted a simulation analysis to obtain preliminary process parameters. Based on the aforementioned research, experiments of vascular scaffold fabrication based on the coaxial jet model and experiments of vascular network fabrication were carried out. Finally, we optimized various parameters, such as the flow rate of internal and external solutions, bioink concentration, and cross-linking agent concentration. The performance tests showed that the fabricated vascular scaffolds had levels of satisfactory degradability, water absorption, and mechanical properties that meet the requirements for practical applications. Cellular experiments with stained samples demonstrated satisfactory proliferation of human umbilical vein endothelial cells (HUVECs) within the vascular scaffold over a seven-day period, observed under a fluorescent inverted microscope. The cells showed good biocompatibility with the vascular scaffold. The above results indicate that the fabricated vascular structure initially meet the requirements of vascular scaffolds.

Electrolytic Graphene Encapsulated CeO2 for Lithium-Sulfur Battery Interlayer Separator

Rare earth elements and graphene composites exhibit better catalytic properties in energy storage materials. The introduction of rare earth oxide and graphene composites as functional layers into the separator to seal the "shuttle effect" formed by polysulfides during the discharge process has proven to be effective. In this study, we prepared CeO2/graphene composites (labeled as CeG) by intercalation exfoliation and in situ electrodeposition methods simultaneously, in which CeO2 was encapsulated in large folds of graphene, which exhibited good defect levels (ID/IG < 1) and its intrinsically superior physical structure acted as a shielding layer to hinder the shuttle of polysulfides, improving the cycling stability and rate of cell performance. The separator cell with CeG achieves an initial discharge specific capacity of 1133.5 mAh/g at 0.5C, excellent rate performance (978.5 mAh/g at 2C), and long cycling (790 mAh/g after 400 cycles).

Dual-Stimuli-Responsive and Anti-Freezing Conductive Ionic Hydrogels for Smart Wearable Devices and Optical Display Devices

Stimuli-responsive hydrogels are a class of important materials for the preparation of flexible sensors, but the development of UV/stress dual-responsive ion-conductive hydrogels with excellent tunability for wearable devices remains a major challenge. In this study, a dual-responsive multifunctional ion-conductive hydrogel (PVA-GEL-GL-Mo₇) with high tensile strength, good stretchability, outstanding flexibility, and stability is successfully fabricated. The prepared hydrogel has an excellent tensile strength of 2.2 MPa, high tenacity of 5.26 MJ/m³, favorable extensibility (522%), and high transparency of 90%. Importantly, the hydrogels have dual responsiveness to UV light and stress, allowing it to be used as a wearable device while responding differently to the UV intensity of different outdoor environments (hydrogels can show different levels of color when exposed to different light intensities of UV light) and can remain flexible at -50 and 85 °C (sensing at both -25 and 85 °C). Therefore, the hydrogels developed in this study have good prospects in different applications, such as flexible wearable devices, duplicate paper, and dual-responsive interactive devices.

New focus of the cloud point/Krafft point of nonionic/cationic surfactants as thermochromic materials for smart windows

A nonionic poly(oxyethylene) monoalkyl ether (C12(EO)6) and a cationic hexadecylpyridinium bromide (HPB) were used to achieve warm/cool transparency transition.

UV Photochromism in Transition Metal Oxides and Hybrid Materials

Limited levels of UV exposure can be beneficial to the human body. However, the UV radiation present in the atmosphere can be damaging if levels of exposure exceed safe limits which depend on the individual the skin color. Hence, UV photochromic materials that respond to UV light by changing their color are powerful tools to sense radiation safety limits. Photochromic materials comprise either organic materials, inorganic transition metal oxides, or a hybrid combination of both. The photochromic behavior largely relies on charge transfer mechanisms and electronic band structures. These factors can be influenced by the structure and morphology, fabrication, composition, hybridization, and preparation of the photochromic materials, among others. Significant challenges are involved in realizing rapid photochromic change, which is repeatable, reversible with low fatigue, and behaving according to the desired application requirements. These challenges also relate to finding the right synergy between the photochromic materials used, the environment it is being used for, and the objectives that need to be achieved. In this review, the principles and applications of photochromic processes for transition metal oxides and hybrid materials, photocatalytic applications, and the outlook in the context of commercialized sensors in this field are presented.

High-Performance Photochromic Hydrogels for Rewritable Information Record

Rewritable information record materials usually demand not only reversibly stimuli-responsive ability, but also strong mechanical properties. To achieve one photochromic hydrogel with super-strong mechanical strength, hydrophobic molecule spiropyran (SP) has been introduced into a copolymer based on ion-hybrid crosslink. The hydrogels exhibit both photoinduced reversible color changes and excellent mechanical properties, i.e., the tensile stress of 3.22 MPa, work of tension of 12.8 MJ m^-3 , and modulus of elasticity of 8.6 MPa. Moreover, the SP-based Ca²⁺ crosslinked hydrogels can be enhanced further when exposed to UV-light via ionic interaction coordination between Ca²⁺ , merocyanine (MC) with polar copolymer chain. In particular, hydrogels have excellent reversible conversion behavior, which can be used to realize repeatable writing of optical information. Thus, the novel design is demonstrated to support future applications in writing repeatable optical information, optical displays, information storage, artificial intelligence systems, and flexible wearable devices.