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Kinetics of demixing and remixing transitions in aqueous solutions of poly(N-isopropylacrylamide):  A temperature-jump H-1 NMR study
KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.ORCID iD: 0000-0002-0231-3970
2006 (English)In: Macromolecular Chemistry and Physics, ISSN 1022-1352, E-ISSN 1521-3935, Vol. 207, no 21, 1972-1979 p.Article in journal (Refereed) Published
Abstract [en]

The time course of the coil-to-globule collapse and intermolecular aggregation of poly(N-isopropylacrylamide) in aqueous solution upon exceeding the lower critical solution temperature (LCST) are investigated by temperature-jump 1H NMR spectroscopy. After the temperature jump, we record the time dependences of (i) the mobile fraction of the polymer chain as revealed by the intensity of the liquid-like NMR signal, (ii) the local mobility of those chains as revealed by the transverse relaxation time T2, and (iii) their self-diffusion coefficient D. The same data are also reported at their temperature-dependent long-time limits. The results suggest a sudden, faster than one second, collapse and intermolecular aggregation into globules and a slower reorganization/redistribution of the individual chains among and within the globular and mobile states. We found that all molecular changes are reversible if the temperature remains less than ca. 6-8 K above the LCST for less than a few minutes; under those conditions, experiments upon sudden temperature quench below the LCST show that the aggregates disintegrate and swell into coils in less than a few seconds.

Place, publisher, year, edition, pages
2006. Vol. 207, no 21, 1972-1979 p.
Keyword [en]
Aggregation, Miscibility, NMR, Temperature jump, Turbidity
National Category
Physical Chemistry
URN: urn:nbn:se:kth:diva-5533DOI: 10.1002/macp.200600394ISI: 000242249500008ScopusID: 2-s2.0-33751082937OAI: diva2:9929
QC 20100921. Uppdaterad från Submitted till Published (20100921).Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2010-09-21Bibliographically approved
In thesis
1. NMR Studies of Colloidal Systems in and out of Equilibrium
Open this publication in new window or tab >>NMR Studies of Colloidal Systems in and out of Equilibrium
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The Thesis describes (i) the development of add-on instrumentation extending the capabilities of conventional NMR spectrometers and (ii) the application of the designed equipments and techniques for investigating various colloidal systems. The new equipments are:

Novel designs of stopped-flow and temperature–jump inserts intended for conventional Bruker wide-bore superconductive magnets. Both inserts are loaded directly from above into the probe space and can be used together with any 10 mm NMR probe with no need for any auxiliary instruments.

A set of 5 mm and 10 mm 1H – 19F – 2H NMR probes designed for heteronuclear 1H – 19F cross-relaxation experiments in Bruker DMX 200, AMX 300 and DMX 500 spectrometers, respectively.

A two–stage low-pass filter intended for suppressing RF noise in electrophoretic NMR experiments.

The kinetics of micellar dissolution and transformation in aqueous solutions of sodium perfluorooctanoate (NaPFO) is investigated using the stopped-flow NMR instrument. The sensitivity of NMR as detection tool for kinetic processes in micellar solutions is clarified and possible artefacts are analysed. In the NaPFO system, the micellar dissolution is found to proceed faster than 100 ms while surfactant precipitation occurs on the time scale of seconds-to-minutes. The kinetics of the coil-to–globule transition and intermolecular aggregation in a poly (Nisopropylacrylamide) solution are investigated by the temperature-jump NMR instrument. As revealed by the time evolution of the 1H spectrum, the T2 relaxation time and the self-diffusion coefficient D, large (>10 nm) and compact aggregates form in less than 1 second upon fast temperature increase and dissolve in less than 3 seconds upon fast temperature decrease.

The intermolecular 1H – 19F dipole-dipole cross-relaxation between the solvent and solute molecules, whose fast rotational diffusion is in the extreme narrowing limit, is investigated. The solutes are perfluorooctanoate ions either in monomeric or in micellar form and trifluoroacetic acid and the solvent is water. The obtained cross-relaxation rates are frequency-dependent which clearly proves that there is no extreme narrowing regime for intermolecular dipole-dipole relaxation. The data provide strong constraints for the dynamic retardation of solvent by the solute.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 55 p.
Trita-FYK, 0601
stopped-flow NMR, temperature-jump NMR, crossrelaxation, NMR, NMR probe, fluorosurfactant, micellar kinetics, micellar structure
National Category
Physical Chemistry
urn:nbn:se:kth:diva-3898 (URN)91-7178-310-5 (ISBN)
Public defence
2006-04-20, Sal F3, Lindstedtsvägen 26, 10:00
QC 20100929Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2010-09-29Bibliographically approved

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