Water freezing remains a perennial topic of great relevance to many important aspects of our lives; from the climate to human society and from economics to medicine, frozen water profoundly ...influences our living environment and life activities. There have been numerous publications on water freezing; however, confusion regarding the process of freezing remains. In this review, we mainly focused on the nucleation aspects of water freezing; in particular, we focused on the effect of the surface morphology and nanostructure of foreign bodies. This review covers the recent progress in ice nucleation and anti-freezing strategies within the framework of nucleation principles. In this regard, we first summarize the crystal nucleation theories. Due to high interfacial energy, ice crystallization is primarily controlled by heterogeneous nucleation events, because the homogeneous nucleation barrier of ice is extremely high. In addition to the interfacial energy, the interfacial morphology or nanostructure of foreign bodies plays a diverse role under different supercooling regimes due to the Gibbs-Thomson effect. This effect gives rise to the inverse homogeneous-like nucleation phenomenon, in which foreign bodies have little influence on the nucleation barrier. This ensures the accurate measurement of the nucleation barrier, critical size, and water-ice interfacial energy, in agreement with the latest studies based on a microemulsions approach, metadynamics, the mW model,
etc.
As a consequence, anti-freezing strategies can be implemented by reducing the nucleation rate through restriction of the contact area of the water/substrate interface, by increasing the heterogeneous nucleation barrier through modification of the interfacial properties of foreign particles, including the interfacial structure and the interaction between the water and foreign particles and by kink kinetics. Within this context, the anti-freezing mechanism of superhydrophobic substrates was reviewed. Therefore, it follows that by significantly reducing the contact area between the water and substrate, superhydrophobic materials can effectively reduce the heterogeneous nucleation rate. We hope that this review will provide a unified picture and guidance for future work on water freezing.
Water freezing remains a perennial topic of great relevance to many important aspects of our lives; from the climate to human society and from economics to medicine, frozen water profoundly influences our living environment and life activities.
A comprehensive review on the five levels of hierarchical structures of silk materials and the correlation with macroscopic properties/performance of the silk materials, that is, the toughness, ...strain‐stiffening, etc., is presented. It follows that the crystalline binding force turns out to be very important in the stabilization of silk materials, while the β‐crystallite networks or nanofibrils and the interactions among helical nanofibrils are two of the most essential structural elements, which to a large extent determine the macroscopic performance of various forms of silk materials. In this context, the characteristic structural factors such as the orientation, size, and density of β‐crystallites are very crucial. It is revealed that the formation of these structural elements is mainly controlled by the intermolecular nucleation of β‐crystallites. Consequently, the rational design and reconstruction of silk materials can be implemented by controlling the molecular nucleation via applying sheering force and seeding (i.e., with carbon nanotubes). In general, the knowledge of the correlation between hierarchical structures and performance provides an understanding of the structural reasons behind the fascinating behaviors of silk materials.
This review presents five levels of hierarchical structures associated with the mechanical performance of silk materials. The crystallization mechanism concerning how silk fibroin molecules self‐organize into crystallites and crystal networks is highlighted, which allows for rational design and sheds light on mesoscopic reconstruction and mesoscopic engineering for synthesizing mechanically enhanced silk materials.
Silk protein is one of the a promising materials for on‐skin and implantable electronic devices due to its biodegradability and biocompatibility. However, its intrinsic brittleness as well as poor ...thermal stability limits its applications. In this work, robust and heat‐resistant silk fibroin composite membranes (SFCMs) are synthesized by mesoscopic doping of regenerated silk fibroin (SF) via the strong interactions between SF and polyurethane. Surprisingly, the obtained SFCMs can endure the tensile test (>200%) and thermal treatment (up to 160 °C). Attributed to these advantages, traditional micromachining techniques, such as inkjet printing, can be carried out to print flexible circuits on such protein substrate. Based on this, Ag nanofibers (NFs) and Pt NFs networks are successfully constructed on both sides of the SFCMs to function as heaters and temperature sensors, respectively. Furthermore, the integrated protein‐based electronic skin (PBES) exhibits high thermal stability and temperature sensitivity (0.205% °C−1). Heating and temperature distribution detection are realized by array‐type PBES, contributing to potential applications in dredging of the blood vessel for alleviating arthritis. This PBES is also inflammation‐free and air‐permeable so that it can directly be laminated onto human skin for long‐term thermal management.
Silk fibroin composite membranes with excellent extensibility, highly heat‐resistant ability, air permeability, biocompatibility, and degradability are candidates for electronic skins (E‐skins) applied in healthcare. Due to these abilities, E‐skins can be mounted onto human skin, thereby simultaneously realizing heating and array‐type temperature detection, even for on‐skin camouflage.
Due to the natural biodegradability and biocompatibility, silk fibroin (SF) is one of the ideal platforms for on‐skin and implantable electronic devices. However, the development of SF‐based ...electronics is still at a preliminary stage due to the SF film intrinsic brittleness as well as the solubility in water, which prevent the fabrication of SF‐based electronics through traditional techniques. In this article, a flexible and stretchable silver nanofibers (Ag NFs)/SF based electrode is synthesized through water‐free procedures, which demonstrates outstanding performance, i.e., low sheet resistance (10.5 Ω sq−1), high transmittance (>90%), excellent stability even after bending cycles >2200 times, and good extensibility (>60% stretching). In addition, on the basis of such advanced (Ag NFs)/SF electrode, a flexible and tactile sensor is further fabricated, which can simultaneously detect pressure and strain signals with a large monitoring window (35 Pa–700 kPa). Besides, this sensor is air‐permeable and inflammation‐free, so that it can be directly laminated onto human skins for long‐term health monitoring. Considering the biodegradable and skin‐comfortable features, this sensor may become promising to find potential applications in on‐skin or implantable health‐monitoring devices.
A biodegradable and stretchable protein‐based sensor with good biocompatibility and high response time is fabricated. It can be used for the human motion detection, such as arm bending and laryngeal movement.
Silk fibroin (SF) has attracted great interest in bone tissue engineering due to its extraordinary characteristics in terms of mechanical properties, biocompatibility, and biodegradability. SF ...scaffolds are assembled by biocompatible polydopamine nanoparticles at mesoscopic scale, which endows the scaffolds with a near‐infrared (NIR) light response for the treatment of bone tumors. The functionalized SF scaffold not only enhances the significant structure and performance of native SF scaffold for bone treatment and reconstruction, such as primary and mesoscopic structure, multi‐level pores, and biodegradation, as well as biocompatibility but also have excellent photothermal effect leading a significant cytotoxicity to MG63 cancer cells after NIR laser irradiation. Moreover, the penetration of NIR light in tissue is improved using an optical fiber, which demonstrates the obtained scaffolds’ great potential in the application of photothermal therapy.
Polydopamine nanoparticles functionalized silk fibroin (PDA@SF) scaffolds are endowed with high photothermal efficiency, outstanding biocompatibility, controllable mechanical properties, and degradation performance to realize both the killing of bone tumor cells and the repairing of bone defects, which are potential candidates for bone tumor therapy.
The Co2P nanoparticles strongly coupled with P-modified NiMoO4 nanorods are designed by a novel carbon encapsulated strategy, representing the highly-active pH-universal electrodes for HER. The ...superior catalytic performance of C-Co2P@P-NiMoO4/NF electrode is mainly deriving from the synergistic coupled effects of multiple metal centers, oxygen vacancies, carbon encapsulated and heterostructure.
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The development of hydrogen evolution reaction (HER) technology that operates stably in a wide potential of hydrogen (pH) range of electrolytes is particular important for large-scale hydrogen production. However, the rational design of low-cost and pH-universal electrocatalyst with high catalytic performance remains a huge challenge. Herein, Co2P nanoparticles strongly coupled with P-modified NiMoO4 nanorods are directly grown on nickel foam (NF) substrates through carbon layer encapsulation (denoted as C-Co2P@P-NiMoO4/NF) by hydrothermal, deposition, and phosphating processes. This novel kind of hierarchical heterojunction has abundant heterogeneous interfaces, strong electronic interactions, and optimized reaction kinetics, representing the highly-active pH-universal electrodes for HER. Remarkably, the C-Co2P@P-NiMoO4/NF catalyst shows excellent HER properties in acidic and basic electrolytes, where the overpotentials of 105 mV and 107 mV are applied to drive the current density of 100 mA cm−2. In addition, a low overpotential of 177 mV at 100 mA cm−2 along with high stability is realized in 1 M phosphate buffer solution (PBS), which is close to the state-of-the-art non-precious metal electrocatalysts. Our work not only provides a class of robust pH-universal electrocatalyst but also offers a novel way for the rational design of other heterogeneous materials bythe interface regulation strategy.
A unique strategy of mesoscopic functionalization starting from silk fibroin (SF) materials to the fabrication of meso flexible SF electronic skin (e‐skin) is presented. Notably, SF materials of ...novel and enhanced properties of the materials can be achieved by mesoscopically reconstructing the hierarchical structures of SF materials, based on rerouting the refolding process of SF molecules by meso‐nucleation templating. Mesoscopic hybridization/reconstruction endows cocoon silk with a robust mechanical and electric performance by incorporating wool keratin (WK) and carbon nanotubes (CNTs) into the mesostructures of SF via intermolecular templated nucleation. Furthermore, the asymmetrical meso‐functional films with biocompatibility and insulation on one side and conductivity on the other (square resistance = 130 Ω sq−1) endow the passive wireless e‐skin exhibited a tunable sensitivity from −1.05 to −6.35 kPa−1 with a lossless measurement range of ≈2 kPa. The pulses of human subjects are monitored using the e‐skin to evaluate blood vessel hardening and real‐time dynamic systolic and diastolic blood pressure.
A unique mesoscopic functionalization strategy from silk fibroin (SF) material for the preparation of mesoscopic flexible SF electronic‐skin is proposed. These revolutionary steps enable meso‐hybrid SF to be adopted to fabricate flexible, biocompatible, and highly sensitive stress sensors for continuous physiological conditions monitoring.
Solid photothermal materials with favorable biocompatibility and modifiable mechanical properties demonstrate obvious superiority and growing demand. In this work, polydopamine (PDA) induced ...functionalization of regenerated silk fibroin (RSF) fibers has satisfactory photothermal conversion ability and flexibility. Based on multilevel engineering, RSF solution containing PDA nanoparticles is wet spun to PDA‐incorporating RSF (PDA@RSF) fibers, and then the fibers are coated with PDA via oxidative self‐polymerization of dopamine to form PDA@RSF‐PDA (PRP) fibers. During the wet spinning process, PDA is to adjust the mechanical properties of RSF by affecting its hierarchical structure. Meanwhile, coated PDA gives the PRP fibers extensive absorption of near‐infrared light and sunlight, which is further fabricated into PRP fibrous membranes. The temperature of PRP fibrous membranes can be adjusted and increases to about 50 °C within 360 s under 808 nm laser irradiation with a power density of 0.6 W cm−2, and PRP fibrous membranes exhibit effective photothermal cytotoxicity both in vitro and in vivo. Under the simulated sunlight, the temperature of PRP fiber increases to more than 200 °C from room temperature and the material can generate 4.5 V voltage when assembled with a differential thermal battery, which means that the material also has the potential for flexible wearable electronic devices.
The regenerated silk fiber (RSF) solution containing polydopamine (PDA) nanoparticles is wet spun to PDA‐incorporating RSF fibers, and then the fibers are coated with PDA via oxidative self‐polymerization of dopamine. Two‐step PDA functionalized silk fibroin fibers are endowed with controllable mechanical properties, remarkable photothermal property, outstanding biocompatibility, and flexibility, which are potential candidates for photothermal therapy or wearable heaters.
To obtain supercapacitors for wearable electronic devices, highly conductive stretchable electrode substrates with excellent tensile recovery are required. However, the simultaneous realization of ...the above mentioned characteristics is difficult. In this study, tough stainless‐steel fibers (SSFs) are employed as the substrates for knitting into stainless‐steel meshes (SSMs), for the fabrication of textile electrodes with typical 2D‐interconnected networks. The obtained knitted networks can transform the angular elasticity of SSFs into the stretchability of the textile electrodes. The electrodes based on the SSM substrates can be obtained via the in situ growth of NiCo2S4 nanosheets covered by CoS2 nanowires, which exhibit a high specific capacity, high rate capability, and excellent cycling stability. Moreover, the first stretchable solid‐state hybrid supercapacitors based on SSM display excellent performances with respect to a high energy density (60.2 Wh kg−1 at 800 W kg−1), remarkable tensile recovery (≤40% elongation), and high stability (≈76.4% capacity retention at 30% strain for 1000 stretching cycles). The highly stretchable supercapacitor is sewn on the elbow of a garment to drive a light‐emitting diode, and it maintains a high performance with respect to the repetitive process of bending and straightening, thus demonstrating the high applicability of the designed SSMs to wearable electronics.
Knitted textile electrodes of typical 2D interconnected networks with special patterns from stainless‐steel fibers are applied in stretchable solid‐state hybrid supercapacitors. The supercapacitors retain 76.4% of the initial capacitance at 30% strain after 1000 stretching cycles, and display excellent electrochemical and mechanical stability, demonstrating high applicability in wearable electronics.
The recent developments in wearable electronics urgently call for high-performance multi-functional fabrics for sensing and power supply. In this study, a carbonized cellulose fabric decorated by ...reduced graphene oxide (CCF@RGO) is fabricated into a robust and wearable multifunctional device, which demonstrates superior performance in pressure sensing and energy harvesting. The intertwined warp and weft structured cotton textiles with different structures can be converted into conductive carbon fabric while retaining their original fabric structure and natural flexibility. It is proved that graphene oxide (GO) has a promotive effect on the thermal decomposition of the cellulose fibers. Due to the buckling structure on the plain weave fabric surface, the prepared CCF@RGO based pressure sensor shows high sensitivity in a wide range. Furthermore, this conductive fabric can also be used in a single-electrode triboelectric nanogenerator (TENG) for harvesting biomechanical energy. Thus, this multifunctional CCF@RGO has potential applications in the fields of wearable electronics, artificial intelligence devices, human-machine interaction, and so forth.
A multifunctional graphene decorated carbonized cellulose fabric was fabricated for human physiological signal monitoring and energy harvesting.
