Conducting Helical Structures from Celery Decorated with a Metallic Conjugated Polymer Give Resonances in the Terahertz Range

Abstract

A method to decorate cellulose-based helices retrieved from the plant celery with a conductive polymer is proposed. Using a layer-by-layer method, the decoration of the polyanionic conducting polymer poly(4-(2,3-dihydrothieno [3,4-b]-[1,4]dioxin-2-yl-methoxy)-1-butanesulfonic acid (PEDOT-S) is enhanced after coating the negatively charged cellulose helix with a polycationic polyethyleneimine. Microscopy techniques and two-point probe are used to image the structure and measure the conductivity of the helix. Analysis of the optical and electrical properties of the coated helix in the terahertz (THz) frequency range shows a resonance close to 1 THz and a broad shoulder that extends to 3.5 THz, consistent with electromagnetic models. Moreover, as helical antennas, it is shown that both axial and normal modes are present, which are correlated to the orientation and antenna electrical lengths of the coated helices. This work opens the possibility of designing tunable terahertz antennas through simple control of their dimensions and orientation.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201706595.polymers. The single polymer chain in vacuums exists in a planar geometry or a helical one, [1] depending on the configuration of the covalent bond connecting monomers on the chain. While polyethylene in the absence of defects at low temperatures is a stiff zig-zag chain, the addition of sterical hindrance in the form of a styrene substituent will make polystyrene helical in geometry at the local scale of angstrom to nanometer. Biopolymers such as proteins (0.5 nm) and DNA (3 nm) are often helical at a somewhat larger scale than the simple synthetic polymers. Supramolecular ordering of proteins generates the helical structures spanning biomembranes in living systems. Chiral structures are abundant in nature. Yet technology does not have the same facility to generate helicity at the nano-, meso-, and microscale. 3D structures are inherently difficult to mass produce using standard top down processing, due to lack of 3D patterning methods. Recent developments of 3D printing enable construction of coils with dimensions above micrometers, while two-photon poly merization enables creation of structures with dimensions of ≈0.1 µm. [2] Deposition of materials through vacuum onto rotating surfaces at glancing angle of incidence, can generate helical geometries in thin films. [3] The transition from thin films with helical inner structure to separated microcoils, as used in electromagnetics, also indicates new possibilities of designing helices for electromagnetic functions in intermediate parts of the electromagnetic spectrum. They typically require good electrical conductors, patterned in a helical geometry, and metals are the standard choice to build such structures.In the absence of scalable production methods, the abundant supply of helical structures from biological organisms has been used. Algae can have helical shapes. Organelles inside plants often use h...

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