Transparent and iridescent photonic films with intelligent responsive ability based on electrospun core-shell nanofibrous membranes.

The fabrication of transparent and iridescent photonic films that possess intelligent responsiveness by membrane electrospinning is challenging due to the lack of periodic changes in the refractive index (RI) of electrospun membranes. Herein, transparent and iridescent photonic films are prepared through electrospinning core-shell polyacrylonitrile/glucose-containing polyvinyl alcohol (PAN/PVA@GLU) membranes, infiltrated with a cellulose nanocrystal/polyvinyl alcohol/glucose (CNC/PVA/GLU) suspension, followed by evaporation-induced co-assembling. The as-prepared transparent and iridescent photonic films exhibited reversible changes in selective reflection wavelengths ranging from the visible light to the near-infrared region in response to alternate changes in the relative humidity (RH). Thus, the films could be used as an alcohol dipstick by choosing solvents with different polarities such as alcohol-water mixtures of different ratios. Moreover, the films were highly deformable with a strain at failure up to 14.91% without a compromise of strength. In sum, the current work demonstrates a strategy for the design and fabrication of transparent and iridescent photonic films with intelligent responsiveness using electrospinning, and a soft material platform for developing scalable colorimetric sensors and optically active components.

Self-Adaptive Rapid Thermal Conductive Fabrics Based on Hygroscopic Shrinkage Response for Personal Cooling and Drying.

Advanced fabrics with thermal wet management capability as low energy consumption media contribute to personal cooling and drying. Nevertheless, it remains a great challenge to obtain intelligent fabrics with adjustable thermal conductivity (TC) capable of bridging the supply and demand between human body temperature and self-adaptive thermal conduction. Herein, we report hygroscopic-shrinkage nanofiber-based fabrics with excellent moisture sensitivity and significant volume shrinkage, which benefits the construction of high-density thermal conductive pathways by absorbing sweat, with a maximum sweat absorption rate reaching up to 1781%. The TC of the shrunken fabric is significantly increased from the initial 0.102 to 0.731 W·m-1 K-1 with a volume shrinkage rate of 89% due to the synergistic effect of van der Waals force, capillary force, viscous resistance, and gravity. Besides, an enhanced TC of the resulting fabrics facilitates rapid heat transfer to the environments. By capturing the surface temperature variations of the fabric after shrinkage and commercially available cotton/Coolmax, we obtained the fabric that releases the same amount of heat in a shorter period of time (3.3 s). With its exceptional personal thermal and wet management properties, this study paves the way for designing new-generation intelligent fabrics capable of creating more comfortable microclimates.

Electrospinning SA@PVDF-HFP Core-Shell Nanofibers Based on a Visual Light Transmission Response to Alcohol for Intelligent Packaging.

A naked-eye detector based on a rapid transmittance response to alcohol was designed to offer real-time and reusable detection of fruit freshness. To ensure the hydrophobicity of the fibrous membrane and high light transmission response to alcohol, fluorine-rich poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with a low refractive index was selected as the shell layer, while sodium alginate (SA) and polyvinyl alcohol (PVA) were selected as the core layer for coaxial electrospinning. The core-shell fibrous detector was obtained by treatment with CaCl2 to form a stable hydrogel and by water flushing to remove PVA. The interior structure of the fiber and its evolution were investigated with increasing SA concentration, which changed from a nonconcentric structure to a core-shell structure. Without SA, nonconcentric structured fibers were obtained due to high flowability and incompatibility between the organic solvent phase of PVDF-HFP and the aqueous phase of PVA. As the SA concentration increased, the enhanced viscosity and surface tension decreased the asymmetric mobility significantly, which competed with the charge attractive forces from the Taylor cone surface, leading to a core-shell structure. The as-spun membranes were opaque due to light scattering at the interface between air and fiber and became light transparent after immersion in a rotten fruit-containing alcohol and acetic acid due to a decreased light loss. The rapidly responsive, reusable fibrous membranes with over 90% light transparency developed here have high potential for application in visual intelligent packaging to monitor the freshness of fruits and vegetables.

Preparation and Applications of Electrospun Optically Transparent Fibrous Membrane.

The optically transparent electrospun fibrous membrane has been widely used in many fields due to its simple operation, flexible design, controllable structure, high specific surface area, high porosity, and unique excellent optical properties. This paper comprehensively summarizes the preparation methods and applications of an electrospun optically transparent fibrous membrane in view of the selection of raw materials and structure modulation during preparation. We start by the factors that affect transmittance among different materials and explain the light transmission mechanism of the fibrous membrane. This paper also provides an overview of the methods to fabricate a transparent nanofibrous membrane based on the electrospinning technology including direct electrospinning, solution treatment after electrospinning, heat treatment after electrospinning, and surface modification after electrospinning. It further summarizes the differences in the processes and mechanisms between different transparent fibrous membranes prepared by different methods. Additionally, we study the utilization of transparent as-spun membranes as flexible functional materials, namely alcohol dipstick, air purification, self-cleaning materials, biomedicine, sensors, energy and optoelectronics, oil-water separation, food packaging, anti-icing coating, and anti-corrosion materials. It demonstrates the high transparency of the nanofibers' effects on the applications as well as upgrades the product performance.

Construction of Natural Loofah/Poly(vinylidene fluoride) Core-Shell Electrospun Nanofibers via a Controllable Janus Nozzle for Switchable Oil-Water Separation.

Developing microstructure and multifunctional membranes toward switchable oil-water separation has been highly desired in oily wastewater treatment. Herein, a controllable Janus nozzle was employed to innovatively electrospin natural loofah/poly(vinylidene fluoride) (PVDF) nanofibers with a core-shell structure for gravity-driven water purification. By adjusting flow rates of the PVDF component, a core-shell structure of the composite fibers was obtained caused by the lower viscosity and surface tension of PVDF. In addition, a steady laminar motion of fluids was constructed based on the Reynolds number of flow fields being less than 2300. In order to investigate the formation mechanism of the microstructure, a series of Janus nozzles with different lengths were controlled to study the blending of the two immiscible components. The gravity difference between the two components might cause disturbance of the jet motion, and the PVDF component unidirectionally encapsulated the loofah to form the shell layer. Most importantly, the dry loofah/PVDF membranes could separate oil from an oil-water mixture, while the water-wetted membrane exhibited switchable separation that could separate water from the mixtures because of the hydroxyl groups of the hydrophilic loofah hydrogen-bonding with water molecules and forming a hydration layer. The composite fibers can be applied in water remediation in practice, and the method to produce core-shell structures seems attractive for technological applications involving macroscopic core-shell nano- or microfibers.

Effects of Polyhedral Oligomeric Silsesquioxane (POSS) on Thermal and Mechanical Properties of Polysiloxane Foam.

The thermal and mechanical properties of polysiloxane foam are greatly improved by the addition of acrylolsobutyl polyhedral oligomeric silsesquioxane (MA0701, hereinafter referred to as MAPOSS), which has double bonds. The morphologies and properties of the polysiloxane composite foam were characterized. The average cell diameter of the composite foams decreased, while the cell density increased with increasing MAPOSS. Meanwhile, MAPOSS can enhance thermal conductivity and thermal stability. Thermal conductivity increased by 25%, and the temperature at the maximum weight loss rate increased from 556 °C to 599 °C. In addition, MAPOSS also promoted heterogeneous nucleation by functioning as a nucleating agent, which can increase cell density to improve the mechanical properties. The compressive strength of the composite foam increased by 170% compared with that of pure foam. In the composite, MAPOSS increased the cross-linking density by acting as a physical cross-linking point and limited the movement of the segments.

Multiple Physically Cross-Linked F127-α-CD Hydrogels: Preparation, Sol-Gel Transformation, and Controlled Release of 5-Fluorouracil.

Pluronic F127 is a thermosensitive polymer that has been extensively studied and utilized in biomedicine. To improve the gelation properties of F127, α-cyclodextrin was introduced by physical interactions, such as forming inclusion complexes, hydrogen bond self-assembly, and hydrophobic interactions, to prepare F127-α-CD hydrogels. This study explored the temperature-dependent sol-gel transition behavior, gelation mechanism, interior morphology, and controlled release of the anticancer drug 5-fluorouracil. Results showed that hydrogel could be obtained at 1.0%-8.0% weight content of F127. The cross-linking points in this system were PEO-α-CD microcrystalline region and micelle with poly(propylene oxide) as the core. The network inside F127-α-CD hydrogels made it stable and conducive for controlled release. Therefore, this hydrogel is a promising drug release system.

Biomimetic Growth of Hydroxyapatite on Electrospun CA/PVP Core⁻Shell Nanofiber Membranes.

In this study, cellulose acetate (CA)/polyvinylpyrrolidone (PVP) core⁻shell nanofibers were successfully fabricated by electrospinning their homogeneous blending solution. Uniform and cylindrical nanofibers were obtained when the PVP content increased from 0 to 2 wt %. Because of the concentration gradient associated with the solvent volatilization, the composite fibers flattened when the PVP increased to 5 wt %. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results confirmed the existence of a hydrogen bond between the CA and PVP molecules, which enhanced the thermodynamic properties of the CA/PVP nanofibers, as shown by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) results. To analyze the interior structure of the CA/PVP fibers, the water-soluble PVP was selectively removed by immersing the fiber membranes in deionized water. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the PVP component, which has a low surface tension, was driven to the exterior of the fiber to form a discontinuous phase, whereas the high-content CA component inclined to form the internal continuous phase, thereby generating a core⁻shell structure. After the water-treatment, the CA/PVP composite fibers provided more favorable conditions for mineral crystal deposition and growth. Energy-dispersive spectroscopy (EDS) and FTIR proved that the crystal was hydroxyapatite (HAP) and that the calcium to phosphorus ratio was 1.47, which was close to the theoretical value of 1.67 in HAP. Such nanofiber membranes could be potentially applicable in bone tissue engineering.

Metabolizable lanthanum-coordination nanoparticles as efficient radiosensitizers for solid tumor therapy.

The clinical potential of radiotherapy cannot be realised as expected due to the inherent radioresistance of tumors. To overcome these problems, radiosensitizers containing heavy metal elements have been used in radiotherapy as efficient radiation dose enhancers. In the present study, we report the design and preparation of novel lanthanum-coordination nanoparticles, and their application as nano-sized radiosensitizers in radiotherapy against solid tumors. Via a simple one-pot hydrothermal route, these nanoparticles were fabricated without any expensive chemical reagents. The polyvinylpyrrolidone molecules used in a typical synthesis could highly enhance the dispersity and bio-compatibility of these nanoparticles. In vitro toxicity studies demonstrated that these nanoparticles had low cytotoxicity, negligible hemolysis, and no effect on blood coagulation. Upon exposure to high energy X-ray radiation, these nanoparticles possessed excellent radiosensitization effects and induced serious cellular death both in vitro and in vivo. In addition, time-dependent bio-distribution and long-term toxicity results for these nanoparticles after intravenous administration indicated their high bio-compatibility. More importantly, these metabolizable nanoparticles could be cleared up after intravenous administration along with time passing. These significant findings promise the prospective use of these nanoparticles as vigorous X-ray radiation-mediated therapeutic agents in coming cancer treatments.