Abstract
ABSTRACT Responsive functional composite fibre mats that are mechanically stable and impervious to water exposure are produced by coaxial electrospinning of thermotropic liquid crystal (LC) core inside a water-based solution of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) forming the sheath. Because thermotropic LCs usually cannot be spun inside water-based solutions due to excessive interfacial tension , a n enabling step is the addition of ethanol or dioxane to the LC as a co-solvent compatible with both core and sheath fluids. This reduces sufficiently that coaxial jet spinning is possible. After spinning, thermal cross-linking of the PVA+PAA sheath yields LC-functionalised fibres that can be manipulated by hand and remain intact even upon full immersion in water. The LC core retains its behaviour, nematics showing well-aligned birefringence and transitioning to isotropic upon heating above the clearing point, and cholesterics showing selective reflection which is even enhanced upon water immersion due to the removal of sheath scattering. Our results pave the way to producing LC-functionalised responsive fibre mats using durable polymer sheaths, thereby enabling numerous innovative applications in wearable technology, and they also open new opportunities to study LCs in confinement, without visible impact of the container walls.
Highlights
Non-woven mats of thin composite fibres produced by electrospinning, in which a polymeric sheath confines and protects one or several cores of liquid crystal (LC), have the potential to be of significant practical value [1,2,3], as they can bring the strongly responsive behaviour of LCs into contexts where they were previously inac cessible
This allows us to use a mixture of water and ethanol as sheath solvent, of great benefit to the coaxial electrospinning experiments, as the interfacial tension to the core is lower than with a purely aqueous sheath solution
Preliminary experiments show that 7% w/w of polymer (1:1 mass ratio of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA)) can be well dissolved in a solvent consisting of 25% w/w ethanol and 75% w/w water, see Supplemental Figure S1
Summary
Non-woven mats of thin composite fibres produced by electrospinning, in which a polymeric sheath confines and protects one or several cores of liquid crystal (LC), have the potential to be of significant practical value [1,2,3], as they can bring the strongly responsive behaviour of LCs into contexts where they were previously inac cessible. Two approaches have been followed for electrospin ning fibres with LC cores. Single-phase spinning can be used, in which polymer and LC are co-dissolved in a common solvent and a coaxial core–sheath structure arises as a result of in situ phase separation as the solvent evaporates in flight [9,14,15,16]. The LC and polymer solution are separated from the start, the LC S.
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