A Solution Selection Model for Coaxial Electrospinning and Its Application to Nanostructured Hydrogen Storage Materials

Abstract

Coaxial electrospinning was used to encapsulate the complex hydride ammonia borane in polystyrene to improve its properties as a hydrogen storage material. A solvent selection system was developed by using the Hansen solubility parameters to facilitate the choice of compatible solvents for core and shell. This enabled systematic optimization of the parameters needed for successful coelectrospinning. This approach has general application for any multiphase electrospinning system, including ones where the core is highly conducting or nonpolymeric. The resulting fiber morphologies depend strongly on the degree of miscibility of core and shell solutions. Fibers spun from immiscible core-shell solutions had a classic coaxial structure. Fibers produced from semimiscible core-shell solutions were highly porous, with inclusions extending through the fiber and an ordered radial and longitudinal distribution of nanoscale pores on the fiber surface. We suggest that this type of porosity may be due to an instability created in the nonaxisymmetric modes at the core-shell interface, resulting in intrusion of the core into the shell polymer. These controllably porous structures have numerous potential applications including materials templating or drug delivery. In the porous fibers, the temperature of the first hydrogen release of ammonia borane is reduced to 85 °C. This result suggests a nanostructured hydride, but a large mass loss indicates that much of the ammonia borane is expelled on heating. The coaxial fibers, in contrast, appear to encapsulate the hydride successfully. The coaxial and porous fibers alike showed no significant release of borazine, suggesting two different suppression mechanisms for this impurity.

Industrial Upscaling of Electrospinning and Applications of Polymer Nanofibers: A Review

“…Coaxial electrospinning is also useful for the encapsulation of nonspinnable materials such as nanoparticles or conjugated polymers exhibiting a poor thermoplastic behavior,114 enzymes, protein, and cells 115. It has been exploited to encapsulate self‐healing materials (dicyclopentadiene and isophorone diisocyanate),116 the complex hydride ammonia which find application for hydrogen storage,117 and several drugs within polymers. In particular, core–shell fibers provide a release pattern different from bi‐component monolithic fibers 118.…”

A method for scale‐up of co‐electrospun nanofibers via flat core‐shell structure spinneret

“…We can see that compared to the single‐fluid electrospinning, the bending path in the co‐electrospinning process is more complex and less regular. This may result from the different conductivities, elastic modulus and viscosities of the two fluids …”

Nanofibrous scaffold with incorporated protein gradient for directing neurite outgrowth

“…The initial burst releases are likely attributed to proteins that were located near the surface of the nanofibers. This may have resulted from the possible mixing of core and shell solutions during electrospinning [49,50,56,58], and this mixing is postulated to occur predominantly in the Taylor cone [30]. Increasing the degree of immiscibility of both core and shell solutions by varying the choice of the respective solvents may attenuate the mixing.…”