Kinetics of demixing and remixing transitions in aqueous solutions of poly(N-isopropylacrylamide): A temperature-jump H-1 NMR study
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
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.
Aggregation, Miscibility, NMR, Temperature jump, Turbidity
IdentifiersURN: urn:nbn:se:kth:diva-5533DOI: 10.1002/macp.200600394ISI: 000242249500008ScopusID: 2-s2.0-33751082937OAI: oai:DiVA.org:kth-5533DiVA: diva2:9929
QC 20100921. Uppdaterad från Submitted till Published (20100921).2006-04-052006-04-052010-09-21Bibliographically approved