Enhanced scattering induced by electrostatic correlations in concentrated solutions of salt-free dipolar and ionic polymers

Rajeev Kumar, Bradley Lokitz, Timothy Edward Long, Bobby G. Sumpter

Research output: Contribution to journalArticle

Abstract

We present a generalized theory for studying the static monomer density-density correlation function (structure factor) in concentrated solutions and melts of dipolar as well as ionic polymers. The theory captures effects of electrostatic fluctuations on the structure factor and provides insights into the origin of experimentally observed enhanced scattering at ultralow wavevectors in salt-free ionic polymers. It is shown that the enhanced scattering can originate from a coupling between the fluctuations of electric polarization and monomer density. Local and non-local effects of the polarization resulting from finite sized permanent dipoles and ion-pairs in dipolar and charge regulating ionic polymers, respectively, are considered. Theoretical calculations reveal that, similar to the salt-free ionic polymers, the structure factor for dipolar polymers can also exhibit a peak at a finite wavevector and enhanced scattering at ultralow wavevectors. Although consideration of dipolar interactions leads to attractive interactions between monomers, the enhanced scattering at ultralow wavevectors is predicted solely on the basis of the electrostatics of weakly inhomogeneous dipolar and ionic polymers without considering the effects of any aggregates or phase separation. Thus, we conclude that neither aggregation nor phase separation is necessary for observing the enhanced scattering at ultralow wavevectors in salt-free dipolar and ionic polymers. For charge regulating ionic polymers, it is shown that electrostatic interactions between charged monomers get screened with a screening length, which depends not only on the concentration of "free" counterions and coions, but also on the concentration of "adsorbed" ions on the polymer chains. Qualitative comparisons with the experimental scattering curves for ionic and dipolar polymer melts are presented using the theory developed in this work.

Original languageEnglish
Article number163336
JournalJournal of Chemical Physics
Volume149
Issue number16
DOIs
Publication statusPublished - 2018 Oct 28
Externally publishedYes

Fingerprint

Electrostatics
Polymers
Salts
Scattering
electrostatics
salts
polymers
scattering
Monomers
monomers
Phase separation
Ions
Polarization
capture effect
Polymer melts
Coulomb interactions
interactions
polarization
Screening
Agglomeration

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Enhanced scattering induced by electrostatic correlations in concentrated solutions of salt-free dipolar and ionic polymers. / Kumar, Rajeev; Lokitz, Bradley; Long, Timothy Edward; Sumpter, Bobby G.

In: Journal of Chemical Physics, Vol. 149, No. 16, 163336, 28.10.2018.

Research output: Contribution to journalArticle

Kumar, Rajeev ; Lokitz, Bradley ; Long, Timothy Edward ; Sumpter, Bobby G. / Enhanced scattering induced by electrostatic correlations in concentrated solutions of salt-free dipolar and ionic polymers. In: Journal of Chemical Physics. 2018 ; Vol. 149, No. 16.
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