Citation: Wrzesi ´ nska, A.; Tomaszewska, E.; Ranoszek-Soliwoda, K.; Bobowska, I.; Grobelny, J.; Ula´ nski, J.; Wypych-Puszkarz, A. Gold Nanoparticles as Effective ion Traps in Poly(dimethylsiloxane) Cross-Linked by Metal-Ligand Coordination. Molecules 2022, 27, 3579. https://doi.org/10.3390/ molecules27113579 Academic Editor: Galder Kortaberria Received: 7 May 2022 Accepted: 31 May 2022 Published: 2 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). molecules Article Gold Nanoparticles as Effective ion Traps in Poly(dimethylsiloxane) Cross-Linked by Metal-Ligand Coordination Angelika Wrzesi ´ nska 1, * , Emilia Tomaszewska 2 , Katarzyna Ranoszek-Soliwoda 2 , Izabela Bobowska 1 , Jaroslaw Grobelny 2 , Jacek Ula ´ nski 1 and Aleksandra Wypych-Puszkarz 1, * 1 Department of Molecular Physics, Faculty of Chemistry, Lodz University of Technology, Zeromskiego 116, 90-924 Lodz, Poland; izabela.bobowska@p.lodz.pl (I.B.); jacek.ulanski@p.lodz.pl (J.U.) 2 Department of Materials Technology and Chemistry, Faculty of Chemistry, University of Lodz, Pomorska 163, 90-236 Lodz, Poland; emilia.tomaszewska@chemia.uni.lodz.pl (E.T.); katarzyna.soliwoda@chemia.uni.lodz.pl (K.R.-S.); jaroslaw.grobelny@chemia.uni.lodz.pl (J.G.) * Correspondence: angelika.wrzesinska@edu.p.lodz.pl (A.W.); aleksandra.wypych@p.lodz.pl (A.W.-P.); Tel.: +48-42-631-32-05 (A.W.-P.) Abstract: At this time, the development of advanced elastic dielectric materials for use in organic devices, particularly in organic field-effect transistors, is of considerable interest to the scientific community. In the present work, flexible poly(dimethylsiloxane) (PDMS) specimenscross-linked by means of ZnCl 2 -bipyridine coordination with an addition of 0.001 wt. %, 0.0025 wt. %, 0.005 wt. %, 0.04 wt. %, 0.2 wt. %, and 0.4 wt. % of gold nanoparticles (AuNPs) were prepared in order to understand the effect of AuNPs on the electrical properties of the composite materials formed. The broadband dielectric spectroscopy measurements revealed one order of magnitude decrease in loss tangent, compared to the coordinated system, upon an introduction of 0.001 wt. % of AuNPs into the polymeric matrix. An introduction of AuNPs causes damping of conductivity within the low- temperature range investigated. These effects can be explained as a result of trapping the Cl − counter ions by the nanoparticles. The study has shown that even a very low concentration of AuNPs (0.001 wt. %) still brings about effective trapping of Cl − counter anions, therefore improving the dielectric properties of the investigated systems. The modification proposed reveals new perspectives for using AuNPs in polymers cross-linked by metal-ligand coordination systems. Keywords: gold nanoparticles; metal-ligand coordination; poly(dimethylsiloxane); broadband dielec- tric spectroscopy; ionic charge carrier trapping 1. Introduction Flexible and stretchable electronics constitute today an emerging technology expected to find multiple applications in the construction of novel optoelectronic devices such as foldable displays, wearable photovoltaic cells, extensible sensors, medical devices, etc. Furthermore, these devices might be easily manufactured at relatively low temperatures and by simple and cost-effective printing processes, thus leading to a substantial cost reduction [1]. The development of modern electronic circuitry demands a range of new materials having different functionalities, beginning with substrates and semiconductors through gate dielectrics and up to the conductive materials for electrodes [2]. All these components should fulfill specific electrical requirements while demonstrating mechanical properties suitable for stretchable and flexible applications. Combining stretchability with a desired electronic functionality constitutes a real challenge in the field of modern materials engineering. A gate dielectric is an example of a material that has been intensively optimized with regard to its composition and processing methods in order to meet specific requirements for thin-film transistors—vital components of each electronic circuit [1,3]. Dielectric per- mittivity (often represented by relative permittivity k = ε/ε 0 ) and dielectric loss are two Molecules 2022, 27, 3579. https://doi.org/10.3390/molecules27113579 https://www.mdpi.com/journal/molecules