Interchain Spacing and Screening Length Modification of PSS Backbone Chains in Zwitterion-Doped Poly(3,4-Ethylenedioxyth
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nterchain Spacing and Screening Length Modification of PSS Backbone Chains in Zwitterion-Doped Poly(3,4Ethylenedioxythiophene):Polystyrene Sulfonate G. E. Péreza, *, A. Alkorbib, A. Iraqib, F. Bastianinia, E. Pinedaa, S. M. Kingc, and A. D. F. Dunbara, ** aDepartment of Chemical and Biological Engineering, Faculty of Engineering, University of Sheffield, Sheffield, S1 3JD United Kingdom b
Department of Chemistry, Faculty of Engineering, University of Sheffield, Sheffield, S3 7HF United Kingdom ISIS Pulsed Neutron and Muon Source, STFC, Rutherford Appleton Laboratory, Didcot, Oxfordshire, OX11 0QX United Kingdom *e-mail: [email protected] **e-mail: [email protected]
c
Received November 12, 2019; revised January 10, 2020; accepted January 17, 2020
Abstract—The interchain spacing and screening length modification of deuterated PSS (d-PSS) backbone chains in zwitterion-doped PEDOT:d-PSS were studied as a function of the doping concentration using small angle neutron scattering. Results suggest that the dopant, 3-(N,N-Dimethylmyristylammonio)propanesulfonate (DYMAP), forms worm-like micelle structures in the PEDOT:d-PSS dispersion that grow in size as the doping concentration increases. The interchain spacing between negatively charged d-PSS remains unaffected by DYMAP up to 15 mM doping concentration. However, from 15 to 25 mM doping concentration, the interchain spacing increases due to steric interactions of grown DYMAP worm-like micelles with the d-PSS chains. At 30 mM doping concentration, the interchain distance between negatively charged d-PSS chains is reduced due to the gelation of the PEDOT:d-PSS dispersion caused by the crosslinking between long DYMAP worm-like micelles and d-PSS chains. Meanwhile, the screening length of the neutralized dPSS segments attached to the PEDOT oligomers increases as the DYMAP concentration increases form 5 to 30 mM due to the neutralization of the negatively charged d-PSS segments by their Coulomb interaction with the cation in DYMAP. Keywords: PEDOT:PSS, small angle neutron scattering, zwitterion, deuteration, correlation length, charge screening, interchain spacing DOI: 10.1134/S102745102007037X
INTRODUCTION Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is one of the most widely used conducting polymers [1], with applications that range from OLED based displays [2, 3] and solar cells [4, 5], to bone regeneration [6] and nanobiointerfaces [7, 8]. This is due to its numerous advantageous characteristics such as its biocompatibilty [9, 10], good thermal and mechanical stability [11–13], excellent water solubility [1], and optical transparency in the visible spectrum when processed as a thin film [14]. However, its intrinsic conductivity is relatively low compared to most inorganic conductors. A widely used technique to improve the conductivity of PEDOT:PSS is the addition of asymmetrically charged dopants such as ionic liquids [15, 16], acids [17, 18], polar solvents [19, 20], alcohols [21, 22], polyelectrolytes, salts [23–26], and surfactants
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