Compressive properties of electrospun fiber mats are reported for the first time. Mats of bisphenol-A polysulfone (PSU) and of poly(trimethyl hexamethylene terephthalamide) (PA 6(3)T) were electrospun and annealed at a range of temperatures spanning the glass transition temperature of each polymer. The data for applied stress versus mat solidity were found to be well-described by a power law of the form !! = ! − ! ! , where !! is the applied stress and ϕ is solidity, in accord with the analysis of Toll. The values of n range from 3.2 to 6 for PSU and from 8.0 to 20 for PA 6(3)T. The lowest values in each case were exhibited by mats annealed near the glass transition temperature of the fiber material. The values of n are independent of fiber diameter. The higher values of n are attributed to fiber slippage via a mechanism analogous to that of work hardening of metals. The values of kE can vary by an order of magnitude and were difficult to determine precisely, due to the nature of the power law and the inhomogeneity of the mats. The compressibility of electrospun mats in response to an applied stress is sufficiently large that it cannot be neglected in applications where large pressures may be involved, such as filtration or membrane separations. In addition to the initial solidity of the mats, the material compressibility and the operating pressure relevant to the application is important to describe the structure of electrospun mats quantitatively under conditions of use.2

Microfiltration of emulsions of oil (dodecane) in water using electrospun membranes of poly(trimethyl hexamethylene terephthalamide) (PA6 (

Osmotically assisted reverse osmosis (OARO) has become an emerging membrane technology to tackle the limitations of a reverse osmosis (RO) process for water desalination. A strong membrane that can withstand a high hydraulic pressure is crucial for the OARO process. Here, we develop ultra-strong polymeric thin film composite (TFC) hollow fiber membranes with exceptionally high hydraulic burst pressures of up to 110 bar, while maintaining high pure water permeance of around 3 litre/(m2 h bar) and a NaCl rejection of about 98%. The ultra-strong TFC hollow fiber membranes are achieved mainly by tuning the concentration of the host polymer in spinning dopes and engineering the fiber dimension and morphology. The optimal TFC membranes display promising water permeance under the OR and OARO operation modes. This work may shed new light on the fabrication of ultra-strong TFC hollow fiber membranes for water treatments and desalination.

Hydraulic permeability of electrospun fiber mats under flow-induced compression has been modeled and verified experimentally. The permeation model accurately estimates the changes in solidity, and hence the permeability of the electrospun mats, over a range of pressure differentials. The model is based on Darcy's law applied to a compressible, porous medium, using Happel's equation for the permeability and Toll's equation for the compressibility of fiber mats. Hydraulic permeability of electrospun mats of bis-phenol A polysulfone (PSU) comprising fibers of different mean diameter, annealed at temperatures at and above the glass transition of the polymer, was measured for feed water pressures ranging from 5 kPa to 140 kPa. The electrospun mats are found to experience a decrease of more than 60% in permeability constant between 5 and 140 kPa due to the loss of porosity resulting from the flow-induced compression.

Confocal laser scanning microscopy with fluorescent markers and index matching has been used to collect three-dimensional (3D) digitized images of electrospun fiber mats and of a borosilicate glass fiber material. By embedding the fluorescent dye in either the material component (fibers) or pore space component (the index matching fluid), acquisitions of both positive and negative images of the porous fibrous materials are demonstrated. Image analysis techniques are then applied to the 3D reconstructions of the fibrous materials to extract important morphological characteristics such as porosity, specific surface area, distributions of fiber diameter and of pore diameter, and fiber orientation distribution; the results are compared with other experimental measurements where available. The topology of the pore space is quantified for an electrospun mat for the first time using the Euler-Poincaré characteristic. Finally, a method is presented for subdividing the pore space into a network of cavities and the gates that interconnect them, by which the network structure of the pore space in these electrospun mats is determined.