Triggered Structural Control of Dynamic Covalent Aromatic Polyamides: Effects of Thermal Reorganization Behavior in Solution and Solid States

Preparation of Perfluorosulfonated Ionomer Nanofibers by Solution Blow Spinning

In this work, we report the preparation of high-purity perfluorosulfonated ionomer (Nafion) nanofibers (NFs) via solution blow spinning (SBS). Fiber formation in solution jet spinning is strongly dependent on the structure of the spinning solution. Upon adding a small amount of poly(ethyleneoxide) (PEO) as a spinning aid to Nafion dispersion, most of the highly ordered Nafion aggregate disappeared, allowing the stable production of bead-free and smooth high-purity NFs (Nafion/PEO = 99/1) by SBS. The microstructure of the blowspun Nafion NFs differed from that of electrospun NFs. In the blowspun NFs, incomplete microphase separation between hydrophilic (ionic) and hydrophobic domains was observed, but the crystallization of CF2-CF2 chains was enhanced owing to the high extensional strain rate and rapid solidification during SBS. These findings provide fundamental information for the preparation and characterization of blowspun Nafion NFs.

Fluorodynamers Displaying Tunable Fluorescence on Constitutional Exchanges in Solution and at Solid Film-Solution Interface

Dynamic covalent polymers-dynamers-are adaptive materials that offer timely variant adaptive macroscopic organization across extended scales. In the current study, imine exchange reactions and fluorescence transfer can occur at the interfaces between various solutions and solid state dynameric films. The fluorescence quenching upon imine formations for designed fluorogen was successfully demonstrated, and this tunable fluorescence was further used to study the re-composition of a solid film. Moreover, the dynamic covalent films also exhibited responsiveness to competing amines and acid/base conditions, both in solutions and solid film-solution interface. This work can provide more insights into interface dynamic chemistry and holds great potential for further applications in optical and biomedical materials.

Organic Liquid Impregnation Behavior into Nanofibrous Membranes: Quantitative Analysis of the Effects of Structural Parameters

This paper reports the effects of structural parameters on organic liquid impregnation behavior into nanofibrous (NF) polymer membranes. The NF membranes were prepared from organic liquidphilic polymers, poly(amide-imide)s (PAIs), by electrospinning. The impregnation velocity of the organic liquid, ethylmethylcarbonate, into the as-spun PAI NF membranes with diameters ranging from 400 to 900 nm was approximately 10-20 times higher than that into commercial cellulose nonwoven membranes. Our theoretical analyses based on the Kozeny-Carman equation and multivariate statistics clearly indicate that in addition to the porosity of the membranes, the variation in fiber diameter as well as the average fiber diameter is a crucial factor for controlling the liquid impregnation behavior.

Ultrasound-assisted synthesis of nanocomposites based on aromatic polyamide and modified ZnO nanoparticle for removal of toxic Cr(VI) from water

In this study, novel nanocomposites (NCs) of aromatic polyamide (PA) and surface modified ZnO nanoparticle with s-triazine heterocyclic ring was introduced for efficient removal of toxic hexavalent chromium (VI) from aqueous solution. The surface of ZnO nanoparticle was modified by s-triazine core silane coupling agent (ZnO-TSC) and PA/ZnO-TSC NCs with different amount of ZnO-TSC nanoparticles (0, 5, 10 and 15wt%) were prepared by ultrasonic irradiation. The synthesized PA/ZnO-TSC NCs were characterized by FT-IR, XRD, FE-SEM, TEM and TGA methods. TEM images showed that ZnO nanoparticles were dispersed homogeneously in the polymer matrix. The adsorption experiments were carried out in batch mode to optimize various parameters like contact time, pH and concentration of metal ion that influence the adsorption rate. The maximum uptakes of Cr(VI) at pH 4.0 was 72%, 81%, 89% and 91% for pure PA, NC5%, NC10% and NC15%, respectively. The kinetic of adsorption was investigated and the pseudo second-order model is an appropriate model for interpretation of adsorption mechanism of Cr(VI) ions.

Functional Aromatic Polyamides

We describe herein the state of the art following the last 8 years of research into aromatic polyamides, wholly aromatic polyamides or aramids. These polymers belong to the family of high performance materials because of their exceptional thermal and mechanical behavior. Commercially, they have been transformed into fibers mainly for production of advanced composites, paper, and cut and fire protective garments. Huge research efforts have been carried out to take advantage of the mentioned characteristics in advanced fields related to transport applications, optically active materials, electroactive materials, smart materials, or materials with even better mechanical and thermal behavior.