The Effect of Glycol Side Chains on the Assembly and Microstructure of Conjugated Polymers

Abstract

Conjugated polymers with glycol-based chains, are emerging as a material class with promising applications as organic mixed ionic-electronic conductors, particularly in bioelectronics and thermoelectrics. However, little is still known about their microstructure and the role of the side chains in determining intermolecular interactions and polymer packing. Here, we use the combination of electrospray deposition and scanning tunneling microscopy to determine the microstructure of prototypical glycolated conjugated polymers (pgBTTT and p(g2T-TT)) with submonomer resolution. Molecular dynamics simulations of the same surface-adsorbed polymers exhibit an excellent agreement with the experimental images, allowing us to extend the characterization of the polymers to the atomic scale. Our results prove that, similarly to their alkylated counterparts, glycolated polymers assemble through interdigitation of their side chains, although significant differences are found in their conformation and interaction patterns. A model is proposed that identifies the driving force for the polymer assembly in the tendency of the side chains to adopt the conformation of their free analogues, i.e., polyethylene and polyethylene glycol, for alkyl or ethylene glycol side chains, respectively. For both classes of polymers, it is also demonstrated that the backbone conformation is determined to a higher degree by the interaction between the side chains rather than by the backbone torsional potential energy. The generalization of these findings from two-dimensional (2D) monolayers to three-dimensional thin films is discussed, together with the opportunity to use this type of 2D study to gain so far inaccessible, subnm-scale information on the microstructure of conjugated polymers.

Side-Chain-Assisted Transition of Conjugated Polymers from a Semiconductor to Conductor and Comparison of Their NO2 Sensing Characteristics

“…The distinct electrical properties of PTQ-TEG , compared to PTQ-T, could be due to the contribution of EG-based side chains because both CPs have the same conjugated framework. To ascertain the effect of the EG-based side chain on the electrical properties of PTQ-TEG , the film morphologies and chain assembly features of both CPs were characterized using AFM and 2D-GIXRD, respectively, because the electrical properties of CPs are known to be sensitively affected by the degree of chain aggregation and assembly [ 49 , 50 ]. As shown in Figure 3 a,b, both CPs exhibited featureless smooth surfaces with root-mean-square (RMS) roughness values of 0.478 nm and 0.355 nm for PTQ-T and PTQ-TEG , respectively.…”

Investigation of the Effect of Poly[poly(ethylene glycol) methyl ether methacrylate] Addition on the Electrochemical Performance of Cellulose-Based Solid- and Gel-Polymer Electrolytes in Lithium-Ion Batteries

“…However, at higher PEGMA concentrations, the increased density of PEGMA chains within the electrolyte can lead to stronger polymer–polymer interactions. These interactions can hinder the absorption and retention of solvent molecules, reducing the swelling ratio . Moreover, the formation of a more interconnected polymer network may occur, resulting in a reduced free volume and limited space for solvent absorption.…”

Low-Regioregularity Polythiophene for a Highly Sensitive and Stretchable Gas Sensor

“…Conjugated polymers have many advantageous properties that make them suitable for use as active layers in optoelectronics; in particular, they can be fabricated at low cost in solution via a simple process. − Their good processing properties in solution are the result of the presence of side chains on the polymer backbone and facilitate the fabrication of affordable large-area devices on plastic substrates. − The side chains of the conjugated polymer also strongly influence the molecular order and device performance. − Asymmetrically arranged alkyl substituents attached to the polymer backbone give rise to two different regioregularities: head-to-tail (HT) and head-to-head (HH). − The regioregularities of polymers are important in that they affect various physical properties of the polymer, such as solubility, modulus, viscoelasticity, thermal behavior, and molecular order. Regioregular side chains enable the molecules to engage in strong van der Waals interactions, which facilitate crystallization. − Therefore, the solution becomes more viscous as the regioregularity increases, and the viscosity of the solution increases with the film thickness. − In particular, as the regioregularity of the polymer molecule increases, the free volume in the polymer decreases, resulting in poor mechanical properties. − A few studies have examined the effects of the positions of alkyl side chains on the molecular order in polymer films; however, the influence of regioregularities on the free volume and the resulting gas adsorption properties remains the subject of extensive discussion.…”