Monitoring undesired pH deviations in the surroundings is one of the most pervasive issues of environment and industry, and developing efficient, economical, portable, and reusable membranes for pH monitoring is urgently needed. Herein, we report novel smart nanomembranes (SNMs) that are made up of anodic aluminum oxide (AAO) templates grafted with spiropyran molecules. The ultraviolet and visible light responses of the SNMs under acid vapors are investigated. Under UV irradiation, the ring-closed spiropyran on the AAO templates transform to ring-opened merocyanine, which contains phenolate oxygen and can be further protonated by acids. Such a protonation process not only shows evident color changes but also endows SNMs with pH-responsive properties, which are further investigated by UV–vis diffuse reflectance spectroscopy. Furthermore, to demonstrate the pH-responsive properties of the SNM, common volatile acids such as hydrochloric acid, nitric acid, formic acid, and acetic acid are tested. The SNM shows conspicuous sensibility, reusability, and reversibility during the processes of irradiation, protonation, and deprotonation. Therefore, the newly developed SNM can be an excellent alternative to the existing pH sensors for the detection of pH variations in environment and industry.
Polyimides (PIs) possess excellent mechanical properties, thermal stability, and chemical resistance and can be converted to carbon materials by thermal carbonization. The preparation of carbon nanomaterials by carbonizing PI‐based nanomaterials, however, has been less studied. In this work, the fabrication of PI nanofibers is investigated using electrospinning and their transformation to carbon nanofibers. Poly(amic acid) carboxylate salts (PAASs) solutions are first electrospun to form PAAS nanofibers. After the imidization and carbonization processes, PI and carbon nanofibers can then be obtained, respectively. The Raman spectra reveal that the carbon nanofibers are partially graphitized by the carbonization process. The diameters of the PI nanofibers are observed to be smaller than those of the PAAS nanofibers because of the formation of the more densely packed structures after the imidization processes; the diameters of the carbon nanofibers remain similar to those of the PI nanofibers after the carbonization process. The thermal dissipation behaviors of the PI and carbon nanofibers are also examined. The infrared images indicate that the transfer rates of thermal energy for the carbon nanofibers are higher than those for the PI nanofibers, due to the better thermal conductivity of carbon caused by the covalent sp2 bonding between carbon atoms.
nanofibrous PI membranes by electrospinning [14] ; the porous hydrophobic membranes were used for oil/water separation.Despite these works, it is still a great challenge to fabricate porous PI-based nanomaterials with controllable morphologies, properties, and sizes. In this work, we develop a novel and facile strategy to fabricate porous PI nanotubes using the template method with a solvent vapor-induced transformation process. The porous PI nanotubes are prepared by wetting the nanochannels of anodic aluminum oxide (AAO) templates with poly(pyromellitic dianhydride-co-4,4′-oxydianiline), amic acid (PAA) solutions using the solution wetting method. By introducing the solvent vapor-induced transformation process, depression of the PAA nanotubes occurs, resulting in the formation of porous PAA nanotubes. After the imidization process at 300 °C and carbonization process at 650 °C, porous PI and carbon nanotubes can be obtained, respectively. The pore lengths of the porous nanotubes can be controlled by changing the type of the annealing solvent and the solvent annealing time.In the past, polymer and carbon nanomaterials have been fabricated using different porous templates. [15][16][17][18][19][20][21][22][23] This work extends the template strategy to prepare nonporous and porous PI nanotubes. The porous PI nanotubes can also be further converted to porous carbon nanotubes, which may have potential applications in areas such as gas separation, capacitors, and energy storage devices. [24][25][26][27] Before preparing the nonporous and porous PAA, PI, and carbon nanostructures, we first examine the PAA, PI, and carbon films coated on glass substrates to confirm the viability of the imidization and carbonization processes. For the imidization process, the N−H bonds of PAA break and the N atoms connect the C atoms to form the imide rings, which can be confirmed by the disappearance of the N-H and O-H stretching bands at 2900-3200 cm −1 in the Fourier transform infrared (FTIR) spectra ( Figure S1a, Supporting Information). The CO stretching bands at 1661 cm −1 for the PAA films are also shifted and changed to symmetric stretching and asymmetric stretching vibration bands at 1777 and 1724 cm −1 , respectively, for the PI films. Moreover, the CN stretching band at 1549 cm −1 for the PAA films is shifted to 1380 cm −1 for the PI films. In addition, the CO bending band at 724 cm −1 is formed for the PI films. Porous Carbon NanotubesPolyimides (PIs) have attracted wide attention because of their exceptional thermal stability and applications in areas such as printed circuit boards and multichip modules. It remains a great challenge, however, to control the morphologies and properties of PI-based nanomaterials, especially porous PI-based nanotubes. In this work, a versatile method to fabricate porous PI nanotubes via the template method is developed, with a solvent vaporinduced transformation process. First, polyamic acid (PAA) solutions are used as precursors and infiltrated into the nanochannels of anodic aluminum oxide...
Abstract1D polymer nanomaterials have attracted significant interest in recent years because of their unique properties and promising applications in various fields. It is, however, still a challenge to fabricate polymer nanoarrays with desired sizes and controlled morphologies. Here, an unprecedented approach, the laser‐assisted nanowetting (LAN) method, to selectively fabricate polymer nanoarrays is presented. Polystyrene (PS) is blended with gold nanorods (AuNRs), which are used to absorb the energy from the laser. After the blend films are brought in contact with AAO templates, the AuNRs at regions shone by the laser beams absorb the energy and heat the surrounding polymer chains, resulting in the formation of PS/AuNRs arrays in selected areas. This work paves a new research direction for developing template‐based polymer nanomaterials.
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