Electrospun Polymer Fibers Containing a Liquid Crystal Core: Insights into Semiflexible Confinement

Abstract

Encapsulation of the nematic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline (MBBA) into the core of poly(vinylpyrrolidone) (PVP) microfibers has been accomplished via coaxial electrospinning for the first time. Data from optical microscopy, two-dimensional Raman mapping, differential scanning calorimetry, and dielectric spectroscopy have been employed to gain detailed insights into the confinement effects on MBBA in a semiflexible polymer sheath. The electrospun fiber diameters could be tuned easily by modifying the flow rate of MBBA, and both the MBBA core and PVP sheath diameters were determined via Raman line cuts. The PVP sheath induced alignment of MBBA, where its long axis is parallel to the fiber axis. Further, the alignment of MBBA led to iridescence in the fibers, which was found to be temperature-sensitive and reversible. Surprisingly, at temperatures below 0 °C, the phase-transition temperatures of confined MBBA are different than the neat and one of its smectic phases is inhibited by the PVP sheath; however, the phases that occur above 0 °C appear to be unrestricted. Thus, electrospun core−sheath fibers with MBBA and PVP provide a useful platform for a semiflexible material, where it is especially necessary to control liquid crystal alignment and polymorphs or phases at low temperature. Overall, the results reported here provide new and important considerations for the effects of confinement on liquid crystals in semiflexible media.

Thermochromic Fibers via Electrospinning

“…Due to growing interest in wearable technology, there is a need for new functional soft, lightweight, elastic materials that facilitate development of wearable devices [1][2][3][4]. Functional fibers that enable sensing without relying on electrical power are of particular interest [2].…”

“…Liquid crystals have been incorporated into the core of core-shell fibers via coaxial electrospinning. Nematic single component N-(4-methoxybenzylidene)-4-butylaniline (MBBA) [3] and multicomponent mixtures [7] were encapsulated within polyvinylpyrrolidone (PVP) based shells. Lagerwall et al demonstrated that non-beaded fiber morphology was required for orientation of the liquid crystal and that confinement within the polymer stabilized the nematic state resulting in an increase in the clearing temperature [7].…”

Selective Bragg reflection of visible light from coaxial electrospun fiber mats

“…Of particular interest are coaxial electrospun fibers with liquid crystalline cores that may be suitable for applications as flexible sensors. [20][21][22][23][24] Nematic liquid crystals possess long-range orientation order but lack translational order. The constituent molecules are highly geometrically anisotropic and achiral.…”

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

“…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 . Some characteristics of electrospun fibers include a large surface area to volume ratio, changes in the crystalline structure, and superior mechanical performance (e.g., increases in tensile strength or flexibility) …”