Porous polym er materials have received great interest in both academic and industrial fields due to their wide range of applications. In this work, a porous polyamide 6 (PA6) material was prepared by a facile solution foaming strategy. In this approach, a sodium carbonate (SC) aqueous solution acted as the foaming agent that reacted with formic acid (FA), generating CO2 and causing phase separation of polyamide (PA). The influence of the PA/FA solution concentration and Na2CO3 concentration on the microstructures and physical properties of prepared PA foams were investigated, respectively. PA foams showed a hierarchical porous structure along the foaming direction. The mean pore dimension ranged from hundreds of nanometers to several microns. Low amounts of sodium salt generated from a neutralization reaction played an important role of heterogeneous nucleation, which increased the crystalline degree of PA foams. The porous PA materials exhibited low thermal conductivity, high crystallinity and good mechanical properties. The novel strategy in this work could produce PA foams on a large scale for potential engineering applications.

Multiple jets ejection in electrospinning has been a major approach to achieving a high production rate of ultrafine fibers, also known as nanofibers. This work studies the effect of solution parameters—including dielectric constant, polarity, conductivity and surface tension—on the jet number and jet evolution in the auxiliary electrode electrospinning approach. The results show that it is easier to generate 2–6 jets with short stable jet length (1.7–6.9 mm) under low voltage (5.03–7.13 kV) when solutions have higher dielectric constant (32.2–78.6) and larger surface tension (31.8–41.29 mN/m). The influence of solution properties on stable jet length and the influence of applied voltage to produce multiple jets are discussed in detail. This work provides a new perspective for understanding jet evolution and mass production of nanofibers in electrospinning.

The electrospinning process is greatly affected by the instability of Taylor cone, an instable point can eject a jet, and multiple instable points can produce multiple jets. A fractal-like multi-jet phenomenon was found in electrospinning process with auxiliary electrodes, and main factors affecting the spinning process were studied experimentally, which included solution viscosity, surface tension, and conductivity. The fractal-like multi-jet is feasible to control the fiber morphology and its output.

A variational principle is established for a moving jet in the electrospinning process to study the vibration property of the jet. A higher accelerated velocity and lower vibration frequency are needed in a multi-needle electrospinning system. This paper introduces an auxiliary electrode to enhance the electric strength, and a numerical analysis is carried out to design an optimal electric field.

Pullulan nanofibers with long-term stabilization were fabricated by using glutaraldehyde as the cross-linking agent and sulfuric acid as the catalyzer via in situ cross-linking electrospinning. The structural, chemical, and thermal analyses have been conducted by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and differential scanning calorimetry. Cross-linked pullulan nanofibers were found thermally more stable. More importantly, the water absorption and water solubility of the cross-linked pullulan nanofiber membranes were evaluated. The results showed that the water absorption rate increased significantly (from 327% to 651%) and the weight loss rate decreased (from 19.0% to 4.1%) with the increase of glutaraldehyde content. Overall, this in situ cross-linking electrospinning technique provides a method to cross-link pullulan during electrospinning.