Influence of Wetting on Morphology and Core Content in Electrospun Core–Sheath Fibers

Abstract

Coaxial electrospinning allows easy and cost-effective realization of composite fibers at the nano- and microscales. Different multifunctional materials can be incorporated with distinct localization to specific regimes of the fiber cross section and extended internal interfaces. However, the final composite properties are affected by variations in internal structure, morphology, and material separation, and thus, nanoscale control is mandatory for high-performance application in devices. Here, we present an analysis with unprecedented detail of the cross section of liquid core-functionalized fibers, yielding information that is difficult to reveal. This is based on focused ion beam (FIB) lift-out and allowing HR-TEM imaging of the fibers together with nanoscale resolution chemical analysis using energy dispersive X-ray spectroscopy (EDS). Unexpectedly, core material escapes during spinning and ends up coating the fiber exterior and target substrate. For high core injection rate, a dramatic difference in fiber morphology is found, depending on whether the surface on which the fibers are deposited is hydrophobic or hydrophilic. The latter enhances postspinning extraction of core fluid, resulting in the loss of the functional material and collapsed fiber morphology. Finally, in situ produced TiO2 nanoparticles dispersed in the polymer appear strikingly different when the core fluid is present compared to when the polymer solution is spun on its own.

Non-electronic gas sensors from electrospun mats of liquid crystal core fibres for detecting volatile organic compounds at room temperature

“…With the SEM we were able to measure the fibre diameters with high precision, finding that all prepared fibres have a base diameter in the range of 4-7 µm. The SEM investigations do not allow us to distinguish core from sheath size, a task that requires sectioning of the fibres by Focused Ion Beam (FIB) prior to imaging of the cross section [51,67], but the POM images shown above demonstrate that the LC filling was rather high. This suggests that the fibre Figure 8.…”

Electrospinning of Tough and Elastic Liquid Crystalline Polymer–Polyurethane Composite Fibers: Mechanical Properties and Fiber Alignment

“…In both of the random and aligned fibers, the SEM images showed minor evidence of fusing of the fibers, or “webbing,” at their intersections. The webbing of adjacent fibers is indicative of incomplete solvent evaporation after the polymer jet has impacted the target . As the solution approaches the target, the polymer is in a “gel‐like” state and continuous evaporation of the solvent solidifies the polymer into fibers.…”

“…Solvent resistance, thermal durability, and mechanical toughness have limited these polymers to be processed in ways that allow for thinner fibers. Further, a limited number of techniques have been employed to access thinner fiber diameters, namely, electrospinning, blow‐spinning, and drawing and each of them has had varied success. Of the available techniques, electrospinning has been arguably the most widely used because of its ability to easily produce nanoscale fibers with a variety of morphologies .…”

“…Traditionally, electrospinning has been performed mostly with polymers that offer some limitations in properties (e.g., brittleness or sensitivity to humidity) such as poly(lactic acid), poly(vinylpyrrolidone), and poly(vinyl alcohol) because they are soluble in solvents that are ideal for electrospinning (e.g., high dielectric constant and high vapor pressure) . Thus, examples of electrospun high‐performance polymers are limited because of the polymers’ incompatibility with the appropriate solvents.…”

Elastic sheath–liquid crystal core fibres achieved by microfluidic wet spinning

“…To collect the fibres, we additionally prepared hydrophobised glass slides: as reported by Kim et al 32 and by Kye et al, 8 the use of hydrophobic substrates is necessary to avoid fibre collapse during the drying process. This was done by the silanisation of the glass surfaces, similar to the method used for treating the glass capillaries, followed by baking at 115 1C under vacuum for at least 30 min and then left to dry overnight at room temperature.…”