Single crystal fibers (SCF) are considered to be a combination of bulk crystals and conventional fibers, thereby possessing the stable physical and chemical properties accompanied with excellent waveguide properties. This paper gives a detailed introduction to the development history of single crystal fibers, including the evolution of the growth technique and the optimization of the growth process. Laser-heated pedestal growth (LHPG) and Micro-pulling-down (μ-PD) methods are considered to be the most widely used growth techniques for growing single crystal fibers, and the advantages of the two methods are also introduced in detail. The second part of this paper describes the characterization of single crystal fibers, including diameter fluctuation, crystal quality and optical losses. A series of cladding approaches for SCF, such as magnetron sputtering, sol–gel, liquid phase epitaxy, co-drawing LHPG, ion implantation and micro-structure cladding will be reviewed. In addition, the research status of single crystal fiber laser and single crystal fiber sensor are also summarized in view of the current research foundation.
Single crystal fiber (SCF) is a diversified functional crystal material. The growth methods, characterization method, cladding approaches and applications of SCF are described in detail.
Hydrophobic interaction chromatography (HIC) as an indispensable method for protein purification has attracted considerable attentions of researchers as well as biopharmaceutical industries. However, the low binding capacity and slow adsorption rate of the currently available HIC media lead to a little supply and high price of the highly purified proteins. Herein, nanofibrous membranes with hydrophobic binding sites were developed for HIC by directly coupling phenyl glycidyl ether on the hydrolyzed cellulose acetate nanofiber membrane (cellulose-phenyl NFM). Scanning electron microscope (SEM), water contact angle (WCA), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) surface area analysis and capillary flow porometer (CFP) were applied to evaluate the physically and chemically structural transformation. The obtained cellulose-phenyl NFMs showed a proper hydrophilcity (WCA = 37°), a relatively high BET surface area (3.6 times the surface area of commercial fibrous membranes), and tortuous-channel structure with through-hole size in the range of 0.25–1.2 μm, which led to a little non-specificity adsorption, high bovine serum albumin adsorption capacity of 118 mg g−1, fast adsorption process within 12 h, good long-term stability and reusability. Moreover, compared with traditional modification methods which always include activation and graft two steps, direct coupling method is more efficient for HIC media fabrication. Therefore, cellulose-phenyl NFMs with outstanding protein adsorption performance could be a kind of promising candidate for HIC.
Smart textiles are attracting great interest. Particularly, air-conditioning textiles are highly desired for their merits in energy conservation and personal temperature/humidity management. Currently, air-conditioning textiles can be fabricated by two strategies. One uses infrared-radiation-adaptive materials, and the other uses moisture-responsive actuators that can regulate temperature and humidity simultaneously. Here, the fabrication of a silk-yarn switch comprising electrospun highly aligned nanofibers is reported and its application in air-conditioning textiles is demonstrated. Silk yarn rotates in contact with liquid, and can be recovered by drying. The different responses and wetting behaviors of the switch to H2O and C2H6O is investigated. It is argued that alignment and surface hydrophilicity of nanofibers play important roles in this term. To elaborate, actuating trait is mainly controlled by reduction of the surface free energy of aligned silk nanofibers, during the wetting process. As proof of concept, the application of the sweat-driven silk-yarn switch in regulating the temperature/humidity of the human body is demonstrated in this work. Considering the large production, versatile processibility, and good biocompatibility, silk actuator may have practical applications in designing smart switches (or valves) for intelligent textiles, artificial muscles, and other application scenarios.
This article reports that extremely thin nanobelts (thickness ~ 10 nm) exhibit pseudocapacitive (PC) charge storage in the asymmetric supercapacitor (ASC) configuration, while show battery-type charge storage in their single electrodes. Two types of nanobelts, viz. NiO–Co3O4 hybrid and spinal-type NiCo2O4, developed by electrospinning technique are used in this work. The charge storage behaviour of the nanobelts is benchmarked against their binary metal oxide nanowires, i.e., NiO and Co3O4, as well as a hybrid of similar chemistry, CuO–Co3O4. The nanobelts have thickness of ~ 10 nm and width ~ 200 nm, whereas the nanowires have diameter of ~ 100 nm. Clear differences in charge storage behaviours are observed in NiO–Co3O4 hybrid nanobelts based ASCs compared to those fabricated using the other materials—the former showed capacitive behaviour whereas the others revealed battery-type discharge behaviour. Origin of pseudocapacitance in nanobelts based ASCs is shown to arise from their nanobelts morphology with thickness less than typical electron diffusion lengths (~ 20 nm). Among all the five type of devices fabricated, the NiO–Co3O4 hybrid ASCs exhibited the highest specific energy, specific power and cycling stability.
Recently, researches on artificial muscles for imitating the functions of the natural muscles has attracted wide attention. The fiber-shape actuators, shape-memory materials or deforming devices, which are similar to human muscle fiber bundles, have extensively studied and provided more possibilities for artificial muscles. Herein, we develop a thermal responsible fiber-shaped actuator based on the low-cost hollow polyethylene fiber. The sheath-core structured fibrous actuators and the stainless-steel conductive yarn winded pre-stretched polyethylene actuators are fabricated with the heating assisted pre-stretching procedure. The actuation mechanism of the thermal-responsive orientation change of molecular chains driving the actuation is discussed and demonstrated by 2D XRD patterns. These polyethylene-based fibrous actuators displayed three significant advantages including (i) color-turning and shape-changing bifunctional response, (ii) direct joule heating actuation and (iii) effective contraction (18% shrinkage of the pristine length) and lifting ability (the ratio of lifting weight to self-weight is up to 50).
Stimuli-responsive materials with switchable wettability have promising practical applications in oil/water separation. A novel CO2-responsive cotton fabric for controlled oil/water separation was fabricated based on mussel-inspired reaction and polymerized with 2-(dimethylamino)ethyl methacrylate (DMAEMA). As expected, the modified fabric exhibited switchable hydrophilicity and hydrophobicity after CO2/N2 alternation, and it could be used for gravity-driven CO2-controlled oil/water separation. Water was selectively penetrated through the fabric and separated from oil after treating by CO2. A reversed wettability could be generated through simply treated with N2. It is expected that the as-prepared fabrics could be applied in smart oil/water separation due to the attractive properties of CO2-switchable system.
Ductile and damage-tolerant fibers (DDTFs) are desired in aerospace engineering, mechanical engineering, and biomedical engineering because of their ability to prevent the catastrophic sudden structural/mechanical failure. However, in practice, design and fabrication of DDTFs remain a major challenge due to finite fiber size and limited processing techniques. In this regard, animal silks can provide inspirations. They are hierarchically structured protein fibers with an elegant trade-off of mechanical strength, extensibility and damage tolerance, making them one of the toughest materials known. In this article, we confirmed that nanofibril organization could improve the ductility and damage-tolerance of silk fibers through restricted fibril shearing, controlled slippage and cleavage. Inspired by these strategies, we further established a rational strategy to produce polyamide DDTFs by combining electrospinning and yarn-spinning techniques. The resultant polymeric DDTFs show a silk-like fracture resistance behavior, indicating potential applications in smart textile, biomedicine, and mechanical engineering.
Photoresponsive supramolecular gels as intelligent non-invasive responsive materials can undergo changes in color, state, morphology and electronic properties upon photo irradiation, making them attractive for a variety of applications. Herein, a novel supramolecular hydrogelator DBE with 1,4-divinylbenzene as the central core, connected via amide linkage to l-phenylalanine and peripheral hydrophilic groups, was designed to evaluate the effect of [2 + 2] photocycloaddition reaction on supramolecular hydrogels. UV irradiation decreases the solubility of the hydrogelator DBE and hence, causes the destruction of the gel. SEM images clearly show that irradiation with UV light could induce disintegration of the right-handed helical nanofibers entangled network, which turns into nanoparticles and eventually massive crystals. Circular dichroism and vibrational circular dichroism data also indicate the formation of right-handed helical nanofibers in DBE gel. FTIR and MALDI–TOF–MS spectrum confirm that the variation of stability and aggregated morphology of DBE gel after UV irradiation is attributed to [2 + 2] cycloaddition reaction of vinyl units. This study presents a wonderful model for regulating the stability and aggregated morphology of supramolecular hydrogels via photo irradiation, as well as offers new ideas for designing novel photo responsive materials.