Electrospun nanofibre diameters

There are some commercially available electrospinning processes, such as the Nanospider electrospun nanofibres, which can provide thin coatings on traditional filtration substrates and enhance the filtration performance of these materials many fold. This technology can yield nanofibres with a narrow diameter distribution and distinct diameter size that can be used to optimise the filtration behaviour of the filter substrates for many applications, where particle retention efficiency is a critical requirement. These suhmicron fibres can significantly improve the air filtration efficiency of a variety of media and filters. The submicron fibres provide improved filter efficiency in the interception and inertial impaction regimes. ... 

The physical characteristics of electrospun nanofibres, such as fibre diameter, depend on various parameters which are divided into three main categories (a) solution properties (solution viscosity, solution concentration, polymer molecular weight, and surface tension) (b) processing conditions (applied voltage, volume flow rate, spinning distance, and needle diameter) and (c) ambient conditions (temperature. 

Preliminary studies were performed to find the optimum conditions for electrospinning PVA solutions. As the polymer concentration increased, a mixture of beads and fibres was formed. Therefore, a PVA concentration of 10% was used for preparation of electrospun nanofibres. A series of mats were prepared from the 10% PVA solution in a mixture containing various amounts of ferric chloride or ammonium persulfate as oxidant at the 15 kV constant electric field. SEM photomicrographs of electrospun PVA nanofibres from a 10% solution showed the presence of uniform nanofibres with diameters ranging from 150 to 400 nm, with an average diameter of 350 nm. 

Zhang J, Lin T and Wang X (2010) Electrospun nanofibre toughened carbon/epoxy composites Effects of polyetherketone cardo (PEK-C) nanofibre diameter and interlayer thickness. Compos Set Techol 70 1660-1666. 

In the past 10 years, electrospun nanofibrous membranes have been spotlighted as an effective filter media to capture fine particles. In addition to the basic studies of electrospinning process to better understand the membrane construction process, researchers from all over the world focus on the study of the relationships between the structure characteristics of electrospun nanofibrous membranes (fiber diameter, pore size, porosity, surface area, etc.) and filtration performances (filtration efficiency, pressure, air permeability, etc.). In this chapter, recent advances in fabricating nanofibrous filter media via electrospinning process have been reviewed. In particular, filtration performances and relevant mechanical properties are discussed in detail. It is interesting that the electrospun nanofibrous membranes have been able to outperform conventional nonwoven membranes fabricated essentially by using the meltblown or spunbonded process. 

Despite recent advances toward the development of electrospun nanofibrous media for particle filtration, challenges in this area have also been met, and many practical problems have to be solved. First, the control of the morphology of electrospun nanofibrous membranes, such as fiber diameter and its distribution. 

Pore size is directly related to the filtration performance. Unlike the sieve, electrospun nanofibrous filters do not have regular pores. The effective maximum pore size of electrospun filters is reflected as the maximum size of particles which can pass through the interconnected tortuous path of the membrane. In practice, the maximum pore size and mean flow pore size are measured by means of a capillary porometer [76], Hussain and co-workers correlated the mean fiber diameter and pore size of ENMs [77], In Fig. 13.4, they found that both values of bubble-point pore size and mean flow pore size could be positively correlated with fiber diameters. The average correlation ratio of the geometric pore size (diameter) to the fiber diameter amounted to about 6. The number became about 5 for the mean capillary pore size (mean flow pore size) and about 9 for the largest capillary pore... 

Measuring mechanical properties of single electrospun nanofibres with above-mentioned techniques reveals a feamre in electrospun nanofibres that are different from their conventional counterparts. It has been found that axial modulus and ultimate tensile strength of electrospun polymeric nanofibres increase abmptly when the fibre diameter is below a certain value (Fig. 4.25) [229, 251-253]. 

In recent years, research interest on electrospinning has shifted from fabrication at the laboratory level to applications. The extremely small diameters of electrospun nanofibres, coupled with the high surface area and interconnected fibrous networks, make them desirable for a wide range of applications [6]. 

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