Marco Zaccaria

Effect of oxide nanoparticles on thermal and mechanical properties of electrospun separators for lithium-ion batteries

This study reports the fabrication and characterization of poly(ethylene oxide) (PEO) and poly(vinylidenefluoride-cochlorotrifluoroethylene) (PVDF-CTFE) nanofibrous separators for lithium-ion batteries loaded with different amounts of fumedsilica and tin oxide nanoparticles. Membrane morphological characterization (SEM, TEM) showed the presence of good-quality nanofibres containing nanoparticles. Thermal degradation and membrane mechanical properties were also investigated, and a remarkable effect of nanoparticle addition on membrane mechanical properties was found. In particular, PEO membranes were strengthened by the addition of metal oxide, whereas PVDF-CTFE membranes acquired ductility.

Plasma assisted nanoparticle dispersion in polymeric solutions for the production of electrospun lithium battery separators

Electrospun nanofibrous mats loaded with inorganic nanoparticles can find application as separators for lithium-ion batteries. A good disaggregation of nanoadditive in the starting polymeric solution is a necessary condition to obtain fibers with homogeneous dispersion of nanoparticles, thus with improved mechanical, thermal and electrical properties. In this work atmospheric pressure non-equilibrium plasma was applied to polymeric solutions to evaluate its effects on nanoparticle dispersion for obtaining electrospun fibers loaded with homogeneously dispersed nanoparticles. To this aim, different kinds of plasma treatments and procedures were implemented and their effect on particle distribution in electrospun fibers was investigated. We demonstrated that plasma is a valuable and effective way to favour nanoparticles dispersion in polymeric solutions.

Study of the effect of atmospheric pressure plasma treatment on electrospinnability of poly-L-lactic acid solutions: Voltage waveform effect

Polymeric nanofibrous mats are currently used for biomedical applications as tissue engineering scaffolds. Electrospinning is an innovative and efficient technology to produce scaffolds starting from a polymeric solution. However, toxic organic solvents must be frequently used to produce fibers with good morphology. In particular, high boiling solvents are often helpful for improving polymer electrospinnability. Nevertheless, toxic traces may be found in the final electrospun mat. In order to minimize the use of organic solvents, particularly the high boiling point ones, while maintaining good electrospinnability of the polymeric solution, the latter can be exposed to plasma. In this work we investigate the use of a novel treatment enabling the production of good quality nanofibers starting from a polymer dissolved in 100% of a low boiling point solvent. This treatment consists in the exposure of the polymeric solution to an atmospheric pressure non-thermal plasma before the electrospinning process. Plasma can be driven by several bias showing different waveforms. In this study the waveform influence on the electrospinnability of the plasma treated solution is investigated.

Electrospinning: A versatile technique for energy storage and sensor applications

The possibility to produce materials for energy storage and piezoelectric sensor applications through the electrospinning technique is here investigated. Electrospun lithium-ion battery separators, piezoelectric sensors are characterized and tested in order to exhibit the outstanding properties of such nanostructured materials which can be successfully implemented on the market.

Electret behavior of electrospun PVdF-based polymers

This paper deals with the electromechanical response of electrospun mats made of PVdF-TrFE, which is generally ascribed to piezoelectric effect. The electric signals detected, on the contrary, do not show a typical piezoelectric response. This could be due to the porous structure of the electrospun specimens or to a more complex behavior. For this purpose, high speed camera pictures, space charge measurements and atomic force microscopy were performed. These measurements showed that the charge stored in the material bulk and on the surface due to electrospinning process and triboelectric effect, respectively, provide an electret behavior to the specimen, which may overwhelm the piezoelectric effect of the polarized β-phase, if any.

Vibration energy harvesting using electrospun nanofibrous PVdF-TrFE

This work is focused on the study of the electromechanical response of fibrous materials produced by means of electrospinning. Such structures are considered an emerging technology for energy harvesting. In particular, PVdF-TrFe co-polymer nanofibers were electrospun and subjected to mechanical vibrations produced by an eccentric shaft. Experimental results showed that the specific electric response to mechanical vibrations, in the frequency range from 15 Hz to 37 Hz, is very high. Moreover, frequency response well follows the vibration source. Cost reduction and a simpler manufacturing technique represent other advantages of the electrospinning process compared to conventional production technologies.

Electrospun PVdF with enhanced piezoelectric behavior

This paper deals with electromechanical response of piezoelectric nanofibrous materials based on PVdF-TrFe co-polymer obtained by means of electrospinning. This technique, providing electrical poling and mechanical stretching during material processing, should increase the beta crystalline phase and thus piezoelectric effect. Two fiber patterns were analyzed, i.e. aligned and random. Experimental results showed that the electric response to mechanical vibrations, in the frequency range from 30 Hz to 200 Hz, is significantly larger for samples with aligned fiber pattern with respect to both commercial films and random fiber specimens. These latters, in fact, show lower beta phase with respect to the aligned-fiber samples.

Effect of atmospheric pressure non-equilibrium plasma treatment on poly-L-lactic acid electrospinnability: Investigating the roles of plasma source and voltage waveform

Summary form only given. Poly-L-lactic acid (PLLA) is a biocompatible and biodegradable polymer, which is soluble in organic solvents, such as dichloromethane (DCM) and dimethylformamide (DMF). The latter is usually added to DCM in appropriate amount in order to increase the dielectric constant of the solution, thus ensuring a better electrospinnability. However, the boiling temperature of DMF is around 153°C (much higher than that of DCM which is about 40°C), and it is therefore difficult to completely avoid traces of residual DMF in the scaffold after the electrospinning process. Electrospun nonwoven mats, composed by nanofibers of high surface area, are suitable substrates for cell growth, therefore the possibility to produce solvent-free scaffolds for biomedical applications is a great chance to increase material compatibility. The aim of this work is to investigate the effect of different plasma sources and voltage waveforms on a PLLA solution in DCM before the electrospinning process (preelectrospinning solution). The focus of the work is the use of non-thermal process to improve the electrospinnability of PLLA in a 100% DCM solution without the need to add the high-boiling point DMF as second solvent to increase conductivity, thus avoiding the use of toxic solvents. Results will be presented concerning the process of exposure of PLLA dissolved at a concentration of 13% w/V in 100% DCM to the plasma generated by (i) a multi-gas plasma jet developed by the authors, (ii) a direct liquid phase discharge reactor and (iii) a gas phase discharge reactor with liquid electrode. Moreover, sinusoidal, triangular and square waveforms with nanosecond or microsecond rise times are here used to drive the plasma sources; the effect of bias and frequency are considered as well: since active species generation and plasma temperature are influenced by these parameters, voltage and frequency have an indirect, though not negligible, influence on electrospinnability improvement. Fiber morphology (fiber diameter distribution, presence of defect such as beads along fiber axis, etc.) and solid state properties of mats produced from a plasma treated solution are compared with those of mats fabricated from an untreated PLLA solution.