Thermochromic Fibers via Electrospinning.

Jimmy Nguyen,Briget E Rabatin,Ratib M Stwodah,Christopher L Vasey,Paola A D’Angelo,Benjamin Atherton,Christina Tang,Kathleen W Swana

doi:10.3390/polym12040842

Abstract

Cholesteryl ester liquid crystals exhibit thermochromic properties related to the existence of a twisted nematic phase. We formulate ternary mixtures of cholesteryl benzoate (CB), cholesteryl pelargonate (CP), and cholesteryl oleyl carbonate (COC) to achieve thermochromic behavior. We aim to achieve thermochromic fibers by incorporating the liquid crystal formulations into electrospun fibers. Two methods of incorporating the liquid crystal (LC) are compared: (1) blend electrospinning and (2) coaxial electrospinning using the same solvent system for the liquid crystal. For blend electrospinning, intermolecular interactions seem to be important in facilitating fiber formation since addition of LC can suppress bead formation. Coaxial electrospinning produces fibers with higher nominal fiber production rates (g/hr) and with higher nominal LC content in the fiber (wt. LC/wt. polymer assuming all of the solvent evaporates) but larger fiber size distributions as quantified by the coefficient of variation in fiber diameter than blend electrospinning with a single nozzle. Importantly, our proof-of-concept experiments demonstrate that coaxially electrospinning with LC and solvent in the core preserves the thermochromic properties of the LC so that thermochromic fibers are achieved.

Highlights

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]
Since liquid crystals alone could not be electrospun into fibers (Figure S1), we explored coaxial electrospinning as a means to produce liquid crystal containing fibers
liquid crystal (LC)/wt. polymer assuming all of the solvent evaporates) but larger fiber size distributions than blend electrospinning with a single nozzle

Summary

Introduction

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]. Cholesteric liquid crystals are a class of unique soft materials with thermochromic properties arising from their molecular structure [6,7]. Cholesteric liquid crystals form a twisted nematic phase [8,9] with a helical structure that have temperature-dependent pitch length [10]. A decrease in temperature causes untwisting of the helical structure leading to an increase in the pitch length [8,9]. The liquid crystal phase appears opaque as the resulting increase in pitch reflects light outside the visible wavelength range. Such materials have been used in Polymers 2020, 12, 842; doi:10.3390/polym12040842 www.mdpi.com/journal/polymers

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Methods

Conclusion