Multiscale structure of poly(ionic liquid)s in bulk and solutions by small angle neutron scattering

TL;DR

This study uses small angle neutron scattering to explore the multiscale nanostructure of poly(ionic liquid)s in bulk and solutions, revealing how side-chain length influences chain conformation and interdigitation, impacting their dynamic properties.

Contribution

It provides the first detailed analysis of how nanostructure affects polymer chain conformation in PILs using SANS, highlighting the role of side-chain length and electrostatic screening.

Findings

Radii of gyration increase with side-chain length in solutions.

Non-monotonic chain size evolution in bulk indicates changes in flexibility.

Evidence of alkyl side-chain interdigitation from structural measurements.

Abstract

Poly(ionic liquid)s (PILs), similar to their ionic liquid (IL) analogues, present a nanostructure arising from local interactions. The influence of this nanostructure on the macromolecular conformation of polymer chains is investigated for the first time by means of an extensive use of small angle neutron scattering on a series of poly(1-vinyl-3-alkylimidazolium)s with varying alkyl side-chain length and counter-anion both in bulk and in dilute solutions. Radii of gyration are found to increase with the side-chain length in solution as a consequence of crowding interactions between neighboring monomers. In bulk, however, a non monotonic evolution of the radius of gyration reflects a change in chain flexibility and a potential screening of electrostatic interactions. Additionally at smaller scale, SANS provides an experimental estimation of both the chain diameter and the correlation length between neighboring chains, comparison of which unveils clear evidence of interdigitation of the alkyl side-chains. These structural features bring precious insights in the understanding of the dynamic properties of PILs.