Morphology Tuning of Electrospun Liquid Crystal/Polymer Fibers

Abstract

This paper elucidates the means to control precisely the morphology of electrospun liquid crystal/polymer fibers formed by phase separation. The relative humidity, solution parameters (concentration, solvent), and the process parameter (feed rate) were varied systematically. We show that the morphology of the phase-separated liquid crystal can be continuously tuned from capsules to uniform fibers with systematic formation of beads-on-a-string structured fibers in the intermediate ranges. In all cases, the polymer forms a sheath around a liquid-crystal (LC) core. The width of the polymer sheath and the diameter of the LC core increase with increasing feed rates. This is similar to the results obtained by coaxial electrospinning. Because these fibers retain the responsive properties of liquid crystals and because of their large surface area, they have potential applications as thermo-, chemo-, and biosensors. Because the size and shape of the liquid-crystal domains will have a profound effect on the performance of the fibers, our ability to precisely control morphology will be crucial in developing these applications.

12‐3: Smart Fabrics Functionalized by Liquid Crystals

“…In this case, we electrospun two solutions -one containing (PVP/5CB/allyl alcohol = 14/21/65, w/w/w) and another containing (PVP/E7/methanol/acetone = 10/15/37.5/37.5, w/w/w/w) at the same time under the same conditions: voltage=22kV, working distance=22cm, and feed-rate=3ml/h, 45% relative humidity. We have found that the humidity can have a profound effect on the fiber morphology [8]. Figure 4 shows the hybrid fiber mat consisting of multiple fibers containing different nematic materials with different clearing points.…”

Responsive Liquid‐Crystal‐Clad Fibers for Advanced Textiles and Wearable Sensors

“…The core provides mechanical strength and absorbs transmitted light, effectively lowering backscattering and thereby enhancing the contrast of the colored fibers (see Figure 1d). [14] Upon application as a uniform film, the LC cladding film will quickly break into beads. [15][16][17][18] This occurs in about 3 s for nematic LCs with low viscosity, and about 50 s for the more viscous CLCs.…”

“…The fiber core has a diameter in the 0.1–0.3 mm range and is used for traditional textiles. The core provides mechanical strength and absorbs transmitted light, effectively lowering backscattering and thereby enhancing the contrast of the colored fibers (see Figure d) …”

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

“…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 . 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) …”

“…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.…”