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.

Multicompartmental “core–sheath” fibers composed of a poly­(caprolactone) (PCL) polymer sheath and poly­(ethylene glycol) (PEG) fluids as the core materials were designed via coaxial electrospinning. Mechanical stretching of the fibers caused a discontinuous mechanical damping or stiffening behavior when the cores were composed of a PEG fluid as a known non-Newtonian shear thickening fluid (PEG and SiO2 particles). Surprisingly, it is found that shear thickening fluids are not a requirement for mechanical damping as is evidenced by similar behavior with Newtonian viscous PEG liquids. Data from optical microscopy, thermogravimetric analysis, dynamic mechanical analysis, and rheology have been employed to gain insights into the interactions between the PCL sheath and the PEG cores. The degree of mechanical damping was found to correlate with the viscosity of the core PEGs and is discussed in terms of the interactions between the core and sheath during mechanical oscillation. In addition, the nonwoven fiber mats were tested for auditory sound attenuation (e.g., white noise, pink noise, frequency steps, and chirps). The fiber mats effectively attenuate sound, especially in the low-frequency regions where their ability to dissipate energy is most prevalent. It is also clear that the degree of sound attenuation is dependent upon the core liquid viscosity. To the best of our knowledge, the results presented here are the first report of mechanical damping behavior in electrospun core–sheath fibers that employ liquid cores to attenuate auditory sound.

Abstract:A poly(dimethylsiloxane-co-(3-aminopropyl)methylsiloxane) polymer (PDMS with 20.3 mol % of (3-aminopropyl)methyl siloxane monomer) has been labeled randomly with 1-pyreneacetyl groups to generate a series of polysiloxanes (Py-PDMS) with pyrenyl contents ranging from 0.7 mol % to 5.2 mol % of the total number of structural units. The remainder of the amino groups were acetylated to avoid intra-chain quenching of the excited singlet states of pyrene via exciplex formation with free amino groups while allowing the formation of excimers to proceed. The fluorescence spectra and temporal decays of the Py-PDMS samples were acquired in tetrahydrofuran (THF), N,N-dimethylformamide (DMF), and dioxane. blob , the average rate constant for intra-chain pyrene excimer formation, was determined from the analysis of the fluorescence decays. blob was found to equal 1.16 (±0.13) × 10 9 , 1.14 (±0.12) × 10 9 , and 0.99 (±0.10) × 10 9 s −1 in THF, DMF, and dioxane, respectively, at room temperature. They are the largest values found to date for any polymeric backbone in these solvents. The qualitative relationship found here between blob and the chemical structures of the polymers indicates that the luminescence characteristics of randomly labeled polymers is a very useful method to probe the long range dynamics of chains of almost any polymer that is amenable to substitution by a lumophore.

Tough and elastic microfiber composites composed of an elastic polyurethane (Hydrothane) and a liquid crystalline polymer (Vectran) are fabricated via electrospinning. The composite fibers (HVC) are examined as a function of the mixing ratio of the polymers and evaluated on the bases of fiber formation, morphology, thermal properties, mechanical performance, and fiber alignment. The fiber diameters of the HVCs decrease as the content of Vectran increases. When the fibers are aligned via a rotating target, they have even smaller diameters and increased uniformity than when a static target is employed. Surprisingly, the aligned fibers’ mechanical properties are different than those of random orientation; the HVC fibers of random orientation display increases in strength, toughness, and elastic modulii when increasing amounts of Vectran are incorporated in the fibers. The aforementioned mechanical properties of the aligned fibers decrease somewhat as the content of Vectran is increased. Further, the durability of the aligned fibers is examined by extensional durability tests over ten cycles. The tests indicate that the HVC fibers are very durable and can function as tunable, tough, and elastic fibrous polymer scaffolds and have potential applications in high‐performance composites, polymeric filtration devices, and fibrous bioengineering materials.