Chemical Oscillation and Morphological Oscillation in Catalyst-Embedded Lyotropic Liquid Crystalline Gels.

Guanying Li,William Cortes,Qizheng Zhang,Ye Zhang

doi:10.3389/fchem.2020.583165

Abstract

Liquid crystalline gels offer promising means in generating smart materials due to programmable mechanics and reversible shape changes in response to external stimuli. We demonstrate a simple and convenient method of constructing catalyst-embedded lyotropic liquid crystalline (LLC) gels and achieve chemomechanical oscillator by converting chemical waves in Belousov–Zhabotinsky (BZ) reaction. We observe the directed chemical oscillations on LLC sticks accompanied by small-scale oscillatory swellings–shrinkages that are synchronized with the chemical waves of an LLC stick. To amplify the mechanical oscillations, we further fabricate small LLC fibers and achieve macroscopically oscillatory bending–unbending transition of the LLC fiber driven by a BZ reaction.

Highlights

Belousov–Zhabotinsky (BZ) reaction performed in low-density media such as in solution gives fascinating rhythmic color oscillations and spatiotemporal patterns
Poly(p-phenylene-sulfoterephthalamide) (S-PPTA) is employed as lyotropic liquid crystalline (LLC) mesogen in this work (Figure 1A) due to (1) its high solubility in water, making it accessible and compatible to perform a BZ reaction in aqueous solution; (2) its lyotropic nematic behavior which is independent of the molar mass of the polymer (Viale et al, 2005); and (3) its negative surface charges, providing the electrical charge attraction for the positively charged metal catalyst, ruthenium(II) tris(bipyridine) chloride in this case
We propose that the mechanical oscillations in LLC gels are due to the transition of molecular assembly between liquid crystal phase and isotropic phase (Figure 4G)

Summary

Introduction

Belousov–Zhabotinsky (BZ) reaction performed in low-density media such as in solution gives fascinating rhythmic color oscillations and spatiotemporal patterns. We have developed post-self-assembly cross-linking approach to construct mixed peptide–polymer oscillatory gels (Zhang et al, 2012a, 2013b). Of liquid crystals to form liquid crystalline gels can further sensitize their response to stimuli, giving rise to macroscale mechanical responses, such as bending, twisting, and buckling (Ware et al, 2015; White and Broer, 2015). In this regard, liquid crystalline gels are the ideal soft material to construct BZ reaction driving mechanical oscillators (Bléger, 2018).

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Results

Conclusion