Fabrication and Thermal Dissipation Properties of Carbon Nanofibers Derived from Electrospun Poly(Amic Acid) Carboxylate Salt Nanofibers

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.     

Design and characterization of PNVCL-based nanofibers and evaluation of their potential applications as scaffolds for surface drug delivery of hydrophobic drugs

In this work, nanofiber scaffolds for surface drug delivery applications were obtained by electrospinning poly(N-vinylcaprolactam) (PNVCL) and its blends with poly(ε-caprolactone) and poly(N-vinylcaprolactam)-b-poly(ε-caprolactone). The process parameters to obtain smooth and beadless PNVCL fibers were optimized. The average fibers diameter was less than 1 μm, and it was determined by scanning electron microscopy analyses. Their affinity toward water was evaluated by measuring the contact angle with water. The ketoprofen release behavior from the fibers was analyzed using independent and model-dependent approaches. The low values of the release exponent (n < 0.5) obtained for 20 and 42 °C, indicating a Fickian diffusion mechanism for all formulations. Dissolution efficiencies (DEs) revealed the effect of polymer composition, methodology used in the electrospinning process, and temperature on the release rate of ketoprofen. PNVCL/poly(N-vinylcaprolactam)-b-poly(ε-caprolactone)-based nanofibers showed greater ability to control the in vitro release of ketoprofen, in view of reduced kinetic constant and DE, making this material promising system for controlling release of hydrophobic drugs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48472.     

A highly transparent and thermally stable copolymer of 1‐adamantyl methacrylate and styrene

Thermal and optical properties of copolymers of 1‐adamantyl methacrylate (AdMA) and styrene (St) prepared by free radical polymerization in the bulk are investigated. The copolymer forms an azeotrope when the composition is AdMA/St = 55/45 mol%. The glass transition temperature and decomposition temperature of the azeotropic copolymer are 170 and ca 340 °C, respectively. The refractive index increases nonlinearly with St content from 1.522 to 1.591. The light scattering loss at 633 nm is 28.1 dB km^?1, which is less than half of that of polystyrene. The total optical loss including molecular vibrational absorption, which is evaluated using a copolymer‐based optical fiber, is 292–645 dB km^?1 at 500–700 nm. These values correspond to transmittances of 86–93% for a 1 m optical path length. © 2014 Society of Chemical Industry     

The effect of temperature on the bending properties and failure mechanism of composite truss core sandwich structures

The effects of temperature on the bending properties and failure mechanism of carbon fiber reinforced polymer composite sandwich structure with pyramidal truss cores were investigated and presented in this paper. The three-point bending tests of composite sandwich structures were performed at seven different temperatures, and the scanning electron microscope was used to examine the fiber-matrix interface properties in order to understand the deformation and failure mechanism. Then the effects of temperature on deformation modes, failure mechanism and bending failure load were studied and analyzed. The results showed that the temperature has visible impact on the deformation modes, failure mechanism, and bending failure load. The bending failure load decreased as temperature increased, which was caused by the degradation of the matrix properties and fiber-matrix interface properties at high temperature. The analytical formulae were also presented to predict the bending stiffness and failure load of composite sandwich structures at different temperatures.     

Mechanical damage characterization of glass fiber-reinforced polymer laminates by ultrasonic maps

A method for simultaneous measurement of the thickness and density for Glass Fiber-Reinforced Polymer (GFRP) laminate plates with ultrasonic waves in C-Scan mode is presented in the form of maps. The method uses three different signals in immersion pulse-echo C-Scan mode. The maps obtained based on the density show the heterogeneity of the material at high resolution at the pixel level (1 × 1 mm²) and therefore they represent an efficient tool to assess and evaluate the damage of the composite structures after manufacturing and after an applied mechanical loading.     

The effects of surface-modified graphene nanoplatelets on the sliding wear properties of basalt fibers-reinforced epoxy composites

Possessing unique designs and properties absent in conventional materials, nanocomposites have made a remarkable imprint in science and technology. This is particularly true regarding the polymer matrix composites when they are further reinforced with nanoparticles. In this study, the effects of different weight percentages (0, 0.1, 0.2, 0.3, 0.4, and 0.5) of surface-modified graphene nanoplatelets (GNPs) on the microhardness and wear properties of basalt fibers/epoxy composites were investigated. The GNPs were surface modified by silane, and the composites were made by the hand lay-up method. The wear tests were conducted under two different loads of 20 and 40 N. The best wear properties were achieved at 0.3 wt % GNPs as a result of the GNPs' self-lubrication property and the formation of a stable transfer/lubricating film at the pin and disk interface. Moreover, the friction coefficient was lower at the higher normal load of 40 N. The microscopic studies by FESEM and SEM showed that the presence of GNPs up to 0.3 wt % led to the stability of the transfer/lubricating film by enhancing the adhesion of the basalt fibers to the epoxy resin. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47986.     

A Flexi-PEGDA Upconversion Implant for Wireless Brain Photodynamic Therapy

Near-infrared (NIR) activatable upconversion nanoparticles (UCNPs) enable wireless-based phototherapies by converting deep-tissue-penetrating NIR to visible light. UCNPs are therefore ideal as wireless transducers for photodynamic therapy (PDT) of deep-sited tumors. However, the retention of unsequestered UCNPs in tissue with minimal options for removal limits their clinical translation. To address this shortcoming, biocompatible UCNPs implants are developed to deliver upconversion photonic properties in a flexible, optical guide design. To enhance its translatability, the UCNPs implant is constructed with an FDA-approved poly(ethylene glycol) diacrylate (PEGDA) core clad with fluorinated ethylene propylene (FEP). The emission spectrum of the UCNPs implant can be tuned to overlap with the absorption spectra of the clinically relevant photosensitizer, 5-aminolevulinic acid (5-ALA). The UCNPs implant can wirelessly transmit upconverted visible light till 8 cm in length and in a bendable manner even when implanted underneath the skin or scalp. With this system, it is demonstrated that NIR-based chronic PDT is achievable in an untethered and noninvasive manner in a mouse xenograft glioblastoma multiforme (GBM) model. It is postulated that such encapsulated UCNPs implants represent a translational shift for wireless deep-tissue phototherapy by enabling sequestration of UCNPs without compromising wireless deep-tissue light delivery.     

Synthesis of highly transparent and thermally stable copolyimide with fluorine-containing dianhydride and alicyclic dianhydride

The development of optical films is highly desirable for applications in flexible displayers. In this work, a copolyimide (co-PI) film with high thermal stability and high transparency was prepared by the copolymerization of 2,2′-bis(trifluoromethyl)-4,4′-diaminodiphenyl ether, cyclobutanetetracarboxylic dianhydride, and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). The effects of aliphatic dianhydride and fluorine dianhydride monomers on the optical, thermal, and mechanical properties of the co-PIs were discussed in detail based on the experimental results and theoretical simulations. We found that the preparation of polyimide (PI) based on the combination of two dianhydrides could obtain the PI film with excellent comprehensive performance due to nonconjugated structure and strong electron-withdrawing effect. Through the structure and composition optimization, a PI film of PI-6FDA-70 with T_g of 300 °C, T_d10% more than 500 °C, the average transparency of 90% and the elongation at the breakage more than 8% was prepared. Such molecular design provides a practical approach to develop high-performance colorless PI films. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48603.     

Structures and mechanical properties of electrospun cellulose nanofibers/poly(ε-caprolactone) composites

Poly(ε-caprolactone) (PCL) is one of the ecofriendly biodegradable polymers with excellent moldability but with rather low mechanical properties especially for the industrial and biomedical use. In this research, to overcome the problem, the two types of cellulose nanofibers, the cellulose acetate nanofibers (CA-NF) and the cellulose nanofibers (C-NF), were composited into PCL for the enhancement of the mechanical properties of PCL. CA-NF were prepared by electrospinning and converted into C-NF afterward by deacetylation. It was found that the Young's modulus of the CA-NF/PCL composite at the fiber concentration of 35 wt% significantly increased by ~3 times as compared with that of neat PCL, whereas C-NF/PCL of the same fiber concentration also increased by ~4.5 times. It was also found that the Young's moduli of CA-NF/PCL nearly reached the theoretical values calculated by the equation suggested by Tsai, but that the Young's moduli of C-NF/PCL could not reach the theoretical values. It indicates that CA-NF possessed better compatibility with PCL than C-NF, agreeing well with the fracture-surface analyses of the two composites by the scanning electron microscopy.