Effect of concentration and ionic strength on the lower critical solution temperature of poly(N-isopropylacrylamide) investigated by small-angle X-ray scattering

Bence Fehér*, Imre Varga, Jan Skov Pedersen

*Corresponding author for this work

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review

Abstract

Thermoresponsive polymers, with special emphasis on poly(N-isopropylacrylamide) (PNIPAAM) have been the focus of several investigations due to its potential applications in many fields of physical and polymer chemistry. PNIPAAM has a “lower critical solution temperature” at 32°C. The LCST can be finely tuned by copolymerization with hydrophobic or hydrophilic comonomers, and with a change of physical chemical parameters, such as ionic strength of the solution. We investigated the effect of polymer concentration on the LCST in two different solution environment, in pure water and in 50 mM NaCl solution with small-angle X-ray scattering (SAXS) of relatively low molecular mass polymers. We showed that the radius of gyration of the pNIPAAM chains increases with the addition of NaCl to the system due to the low level of specific adsorption of chloride ions on the polymer, whilst increasing the temperature causes a shrinkage of the polymer chains. Furthermore, by increasing the temperature the attractive interaction between the individual polymer chains is enhanced which turns into aggregation at the LCST.

Original languageEnglish
JournalSoft Materials
Volume20
IssueS1
Pages (from-to)S10-S18
Number of pages9
ISSN1539-445X
DOIs
Publication statusPublished - 2022

Keywords

  • LCST
  • PNIPAAM
  • SAXS

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