Article pubs.acs.org/Macromolecules
How To Choose Polyelectrolytes for Aqueous Dispersions of Conducting PEDOT Complexes Anna I. Hofmann,†,‡,§ Dimitrios Katsigiannopoulos,†,‡,§ Muhammad Mumtaz,†,‡,§ Ioannis Petsagkourakis,†,‡,§ Gilles Pecastaings,†,‡,§ Guillaume Fleury,†,‡,§ Christophe Schatz,†,‡,§ Eleni Pavlopoulou,†,‡,§ Cyril Brochon,†,‡,§ Georges Hadziioannou,*,†,‡,§ and Eric Cloutet*,†,‡,§ †
Laboratoire de Chimie des Polymères Organiques (LCPO), UMR 5629, Université de Bordeaux, B8 Allée Geoffroy Saint Hilaire, F-33615 Pessac, Cedex, France ‡ Laboratoire de Chimie des Polymères Organiques (LCPO), UMR 5629, Centre National de la Recherche Scientifique (CNRS), B8 Allée Geoffroy Saint Hilaire, F-33615 Pessac, Cedex, France § Laboratoire de Chimie des Polymères Organiques (LCPO), UMR 5629, Institut National Polytechnique de Bordeaux (INP Bordeaux), B8 Allée Geoffroy Saint Hilaire, F-33615 Pessac, Cedex, France S Supporting Information *
ABSTRACT: By using different polysaccharide and polysulfonylimide type polyelectrolytes for the synthesis of aqueous PEDOT:polyelectrolyte dispersions, the influence of the polyelectrolyte backbone and of the anionic groups on the properties of the resulting PEDOT:polyelectrolyte complex has been studied. The obtained PEDOT:polyelectrolyte systems were characterized regarding the doping and the morphology of the complexes in dispersion as well as regarding the optoelectronic properties and the morphology of the dry PEDOT:polyelectrolyte films. Polyelectrolytes with high molar mass, a rigid backbone, and strongly acidic functionalities resulted in highly conducting PEDOT:polyelectrolyte films, while polyelectrolytes with flexible backbones and weakly acidic groups resulted in insulating PEDOT:polyelectrolyte systems. These findings could help to develop a palette of new PEDOT:polyelectrolyte systems, which correspond better to the specific requirements of different applications.
I. INTRODUCTION Over the past decade conducting polymers attracted more and more attention in the scientific community. The development of aqueous dispersions of conducting polymers such as poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) makes it possible to print flexible, transparent, and biocompatible conducting films, which allow the development of a new generation of flexible electronics with a wide range of applications in energy,1−7 entertainment,8−12 and the biomedical field.13−15 Because of its good optoelectronic properties and biocompatibility,16 but also due to a lack of alternatives, the current material of choice for these applications is PEDOT:PSS. However, given the huge variety of applications it would be preferable to design PEDOT:polyelectrolyte systems which meet better the specific requirements. To do so, a better understanding of the stabilization, charge compensation, and doping mechanism in PEDOT:polyelectrolyte complexes is needed. In this article we present a study of different PEDOT:polyelectrolyte complexes, made from polysaccharides and from synthetic bis(sulfonyl)imide substituted polystyrene, investigating the influence of the nature of the polyelectrolyte chain, different acid functionalities, and the density of the charges on the optoelectronic properties of the © 2017 American Chemical Society
PEDOT:polyelectrolyte complex. The use of biopolymers such as dextrane sulfate for PEDOT dispersions could be a way to produce highly biocompatible and cost-efficient conducting polymers,17 whereas the use of bis(sulfonyl)imide substituted polystyrene leads to highly transparent conducting polymers.18 PEDOT is known for its high conductivity in the doped stated and can be synthesized electrochemically, by in situ polymerization or in aqueous dispersion in the presence of an anionic polyelectrolyte.19,20 The latter results in a PEDOT:polyelectrolyte complex which allows easy processing of the conducting polymer through various printing and coating techniques.3,4,7 In the PEDOT:polyelectrolyte complex the anionic polyelectrolyte acts as template and counterion for the positively charged, doped PEDOT and allows the dispersion of the insoluble PEDOT chains in water. Therefore, the nature of the anionic groups, the charge density, and the morphology of the polyelectrolyte play a crucial role for the doping and stabilization of PEDOT. In nature, a huge variety of polyanionic biopolymers, such as polysaccharides, bearing a different Received: November 18, 2016 Revised: February 1, 2017 Published: February 17, 2017 1959
DOI: 10.1021/acs.macromol.6b02504 Macromolecules 2017, 50, 1959−1969
Article
Macromolecules
Figure 1. Chemical structure of (a) pectin, sodium hyaluronate (HLA), and dextran sulfate (DS) and of (b) poly(4-styrenesulfonyltrifluoromethylsulfonyl)imide (PSTFSI), poly(4-styrenesulfonylmethylsulfonyl)imide (PSMSI), (poly(4-styrenesulfonylphenylsulfonyl)imide (PSPSI), poly(methacrylsulfonyltrifluoromethylsulfonyl)imide (PMaTFSI), and PSTFSI-co-poly(acrylic acid) (PSTFSI-co-AA) (m:n = 1:1).
dynamic light scattering (DLS), transmission electron microscopy (TEM), and different atomic force microscopy (AFM) imaging techniques provided information on the morphology of the polymer complex. Furthermore, the charge transport in the conducting films was investigated by temperature-dependent conductivity measurements. The observed characteristics of the PEDOT:polyelectrolyte systems were related to the nature of acidic functionality and the backbone of the polyelectrolyte.
amount of carboxylic or sulfate groups can be found. Figure 1 displays the chemical structure of the different anionic polysaccharides, which were chosen for this work. Pectin (see Figure 1a), which is commercially used as gelling agent and food stabilizer, consists of linear chains of α-(1−4)linked D-galacturonic acid units and of very complex branched derivatives.21 It bears one carboxylic group on every repeating unit, of which 60−70% are esterified and can be hydrolyzed in acidic medium. Hyaluronic acid (see Figure 1a) is a linear polysaccharide composed of D-glucuronic acid and D-Nacetylglucosamine units, linked via alternating β-1,4 and β-1,3 glycosidic bonds, and bears one carboxylic group on every second repeating unit.22,23 It is known for its biomedical application and component in skin care products. Dextran sulfate (see Figure 1a), known as coagulant, is a branched Dglucose polymer, which is highly charged due to 2.4 sulfate groups in average per repeating unit.24 In the continuation of our work on PEDOT:poly(4-styrenesulfonyltrifluoromethylsulfonyl)imide (PSTFSI)18 the three polysaccharides mentioned above were compared to polystyrenesulfonylimide type polyelectrolytes regarding their ability to dope and disperse PEDOT in water. The polystyrenesulfonylimide polyanions bear one negatively charged group per repeating unit and differ in either backbone (poly(methacrylsulfonyltrifluoromethylsulfonyl)imide, PMaTFSI), side group (poly(4-styrenesulfonylphenylsulfonyl)imide, PSPSI; poly(4-styrenesulfonylmethylsulfonyl)imide, PSMSI), or both (PSTFSI-co-poly(acrylic acid), PSTFSI-co-AA) (see Figure 1b). The primary goal of this work was the systematic study of the ability of different types of polyelectrolytes to stabilize and to dope PEDOT in aqueous dispersion. Therefore, PEDOT:polyelectrolyte dispersions with different ratios of PEDOT to polyelectrolyte were synthesized and the obtained PEDOT:polyelectrolyte dispersions were characterized regarding their optoelectronic properties, the doping of the complexed PEDOT, and the morphology of the PEDOT:polyelectrolyte complexes in dispersion and as solid films. UV/vis and Raman spectroscopy techniques were used to characterize the doping of PEDOT, whereas differential scanning calorimetry (DSC),
II. EXPERIMENTAL SECTION Materials. All bis(sulfonyl)imide bearing polyelectrolytes were synthesized by reversible addition−fragmentation chain-transfer (RAFT) polymerization as described elsewhere.18 Hyaluronic acid sodium salt was purchased from Gedeon Richter LTD, Hungary, dextran sulfate sodium salt was purchased from Fluka, Switzerland, and pectin (from apples) was purchased from Solgar, UK, and used without any purification. All PEDOT:polyelectrolyte complexes with different compositions were obtained by an oxidative polymerization of EDOT in the aqueous solution of the respective polyelectrolyte in DI water (resistance
