Temperature- and pH-responsive micelles with collapsible poly(n -isopropylacrylamide) headgroups

Paul A. Fitzgerald, Sushen Gupta, Kathleen Wood, Sebastien Perrier, Gregory G. Warr

Research output: Contribution to journalArticleResearchpeer-review

27 Citations (Scopus)

Abstract

We have studied the micelle formation and phase behavior of a series of temperature- and pH-responsive surfactants prepared by controlled radical (RAFT) polymerization. These C12NIPAMm surfactants consist of a dodecyl tail, a poly(N-isopropylacrylamide) (polyNIPAM) headgroup with average degrees of polymerization of between 7 and 96, and an ionizable carboxylate group. In the un-ionized state, these surfactants phase separate on warming toward a lower critical solution temperature (LCST), which decreases as the length of the NIPAM group is decreased. This is in agreement with the behavior of conventional nonionic poly(ethylene oxide)-based surfactants but is very different from that of polyNIPAM oligomer solutions. Small angle neutron scattering (SANS) shows that these surfactants self-assemble into micelles consisting of a nearly spherical hydrophobic core surrounded by a "hairy" polyNIPAM shell far below their LCST. Upon warming, the micelles undergo a sphere-to-rod transition induced by the collapse of the polyNIPAM shell, causing a reduction in the headgroup area. In the un-ionized state the demixing follows at the LCST, but a single charge on the free polymer end completely suppresses phase separation, allowing micelles to undergo a shape change but remain dissolved. 

Original languageEnglish
Pages (from-to)7986-7992
Number of pages7
JournalLangmuir
Volume30
Issue number27
DOIs
Publication statusPublished - 15 Jul 2014
Externally publishedYes

Cite this

Fitzgerald, P. A., Gupta, S., Wood, K., Perrier, S., & Warr, G. G. (2014). Temperature- and pH-responsive micelles with collapsible poly(n -isopropylacrylamide) headgroups. Langmuir, 30(27), 7986-7992. https://doi.org/10.1021/la501861t