Comparison of Contact Electrification Mechanisms of Selected Polymers and Surface-Functionalized Molecules

Abstract

Among the possible alternatives for the improvement of contact electrification for triboelectric energy harvesting purposes, the functionalization of contact surfaces has attracted wide attention due to its versatility and cost-efficiency. Similarly, low-stiffness polymeric materials such as poly(dimethylsiloxane) (PDMS) are regarded as a promising choice of contact material for the same purpose. However, for defining the most efficient combinations of materials of the aforementioned types, a number of theoretical questions still frequently pose difficulties for practical implementation-related tasks. In this regard, the presented study theoretically assesses the possibilities of consistently selecting optimum performance combinations of contact materials. Here, the optimum is defined as the minimum energy of the charge transfer reaction and, consequently, the maximum density of the predicted triboelectric surface charge. With this aim, the most promising combinations in terms of electron-transfer energies were identified among the candidates of functionalized molecules and polymers. Based on the ordering of materials according to the basic characteristics of charge-transfer reactions�electron and hole affinities�certain differences were observed. These findings indicate that for the materials under consideration, it is not possible to establish a single triboelectric series solely based on a single characteristic. Furthermore, to evaluate the potential compatibility of charge-transfer reaction mechanisms based on electron and material transfer, molecular dynamics simulations were conducted using structures that depict pairs of polymers and self-assembled monolayers of functionalized molecules in contact and separated types of operations. The obtained results indicate that the formation of equally charged free fragments of polymer chains is likely taking place in the contact electrification for N-(2-aminoethyl)-3-aminopropyl trimethoxysilane/PDMS interfaces. At variance, a contact electrification mechanism by charge-dependent material transfer may occur for 1H, 1H, 2H, 2H-perfluorooctyl trimethoxysilane/PDMS interfaces.