Modified conformation and physical properties in conducting polymers due to varying conjugation and solvent interactions

Abstract

Small angle X-ray scattering (SAXS) studies in poly[2-methoxy-5-(2 ' -ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with varying conjugation, and polyethylene dioxythiophene complexed with polystyrene sulfonate (PEDOT-PSS) in different solvents have shown the important role of -electron conjugation and solvent-chain interactions in controlling the chain conformation and assembly. In MEH-PPV, by increasing the extent of conjugation from 30 to 100 %, the persistence length (l p ) increases from 20 to 66 Å. Moreover, a pronounced second peak in the pair distribution function has been observed in fully conjugated chain, at larger length scales. This feature indicates that the chain segments tend to self-assemble as the conjugation along the chain increases. In case of PEDOT-PSS, the chains undergo solvent induced expansion and enhanced chain organization. The clusters formed by chains are better correlated in dimethyl sulfoxide (DMSO) solution than water, as observed in the scattered intensity profiles. The values of radius of gyration and the exponent (water: 2.6, DMSO: 2.31) of * Electronic address: s_paramita@physics.iisc.ernet.in Fax: +91-80-2360 2602 Tel: +91-80-2293 2859power-law decay, obtained from the unified scattering function (Beaucage) analysis, give evidence for chain expansion from compact (in water) to extended coil in DMSO solutions, which is consistent with the Kratky plot analysis. The mechanism of this transition and the increase in dc conductivity of PEDOT-PSS in DMSO solution are discussed. The onset frequency for the increase in ac conduction as well as its temperature dependence probes the extent of connectivity in PEDOT-PSS system. The enhanced charge transport in PEDOT-PSS in DMSO is attributed to the extended chain conformation as observed in SAXS results.

Entanglements in P3HT and their influence on thin‐film mechanical properties: Insights from molecular dynamics simulations

“…This is larger, however, than the persistence length measured experimentally (5 to 7 monomers, 2 to 2.5 nm) . Recall, however, that persistence length is dependent on solvent conditions and regioregularity . As a point of comparison, the persistence length of poly‐methylmethacrylate (PMMA), a widely used commercial polymer, is 0.3 nm, which is an order of magnitude smaller than that of P3HT and reveals the comparatively stronger rigidity of the P3HT conjugated backbone.…”

Structural and Conformational Chemistry from Electrochemical Molecular Machines. Replicating Biological Functions. A Review

“…The number of positive charges on every chain of the conducting polymer and the concentration of solvent and counterions inside the film is changing. Experimental results indicate that, for some polymer‐counterion systems, by changing the solvent or the salt the driving electrochemical reaction can change . Bending and linear artificial muscles translate ionic exchanges to macroscopic movements: they are useful tools to identify and quantify reaction‐driven ionic exchanges under different experimental conditions.…”

Thermoelectric Materials: A Brief Historical Survey from Metal Junctions and Inorganic Semiconductors to Organic Polymers

“…Hence the dispersions are believed to consist of phase‐segregated grains of highly conducting and hydrophobic regions rich in PEDOT surrounded by a shell formed by excess hydrophilic and insulating PSS 106. In aqueous solution, the chains are suggested to have a coil‐like structure, and in the presence of conductivity‐boosting additives it has been proposed that these compact coils expand, facilitating connectivity between grains in the final films 107…”