| dc.description.abstract | (1) A comparative study of PVDF nanofibrous membranes prepared by continuous near-field and conventional electrospinning processes:
A comparative study utilizing both continuous near-field electrospinning (CNFES) and conventional electrospinning processes of electrospun poly vinylidene fluoride (PVDF)-based membranes (EPMs) is presented in this paper. The fiber morphology and average fiber diameter (AFD) of the EPMs are observed by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) is used to compare the possible modifications in crystal structure and thermal properties. Fourier Transform Infrared Spectroscopy (FTIR) is used to study the crystalline isomers of PVDF EPMs. Results indicate that EPMs prepared by CNFES exhibit slightly lower relative intensities at the infrared absorption bands than the conventional electrospinning counterparts, owing to its smaller size of crystallite. Moreover, the CNFES electrospun fiber are revealed to have relatively higher crystallinity of 40.78%, as compared with conventional ones of 33.72%. However, DSC results indicate that both CNFES and conventional EPMs share similar thermographs in endothermic peaks extending from 156°C to 174°C, despite the significant differences in AFD. Finally, the critical length of PVDF nanofibers is characterized experimentally and theoretical prediction of is in well agreement with the experimental observations of .
(2) Self-Organization of multiple jets in Near-Field Electrospinning Process:
In this paper, a dispersion law analysis and critical value of applied electric field intensity/field strength formulations are employed to investigate the self-organized behavior of multiple jets in near-field electrospinning (NFES) experiments. In particular, the theoretical “fastest forming instability” in mesocopic scale plays a crucial role in selecting a specific characteristic wavelength. The onset of electrospinning from a free liquid surface is experimentally observed from the porous material sandwiched by 2 flat copper electrodes and NFES setup of electrified 8 wt% polyethylene oxide (PEO) polymeric solution. Predicting critical values of the critical field strength and corresponding critical interjet distance i.e., the maximal distance between the neighboring jets, is also deduced and validated to be simply depends on the capillary length. Subsequently, a modified theory based on the addition of hydrostatic, capillary and electric pressures is proposed to compensate the deviation of NFES experiment and theory of conventional electrospinning from free liquid surface. The extra capillary pressure term is curve-fitted and found to be effective to reduce the deviation in interjet distance range of 3-5mm, which falls into the regime of NFES at the similar scale of electrode-to-collector distance.
(3) Pattern transfer of Aligned Metal nano/micro wires as flexible Transparent Electrode using Electrospun Nanofibers template:
Owing to scarcity and high cost of indium, predominantly used indium tin oxide (ITO) films as transparent electrodes have attracted great attention in finding potential replacement such as solution-processed networks of carbon nanotubes (CNTs), graphene, and silver nanowires (NWs). More recently, electrospun copper NWs as high-performance electrodes which high aspect ratio of 100,000 and 90% transmittance at 50Ω/sq was experimentally achieved. However, the fabrication route of the Cu nanofibers (NFs) web includes two high temperature processes (calcinated 2h in air at 500◦C and annealed 1h in hydrogen at 300◦C, respectively). In this paper, we proposed a new method in obtaining a metal nano/micro wires as flexible transparent electrode using electrospun NFs templates and dry pattern transfer process. Our proposed method is advantageous in easily tuning the conductivity and transmittance (T) via sputtering time in minutes without the need of time-consuming high temperature thermal steps. Here, we show comprehensively transferred high-performance transparent electrodes with platinum (Pt)-coated NWs electrodes by a facile and scalable electrospinning combined sputtering process. Pt-coated NWs have high aspect ratios of up to 5000 and sputtered with Pt to reduce junction resistance, which result in high T at low sheet resistance, e.g., 90% at 131 Ω/sq. The Pt-coated NWs electrodes also show great flexibility and stretchabilty, which easily surpass the brittleness of ITO films.
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