J. Godward et al., GELATION OF AQUEOUS-SOLUTIONS OF DIBLOCK AND TRIBLOCK COPOLYMERS OF ETHYLENE-OXIDE AND 1,5-BUTYLENE OXIDE STUDIED BY H-1 NUCLEAR MAGNETIC-RELAXATION, Journal of the Chemical Society. Faraday transactions, 91(19), 1995, pp. 3461-3468
Citations number
23
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
H-1 NMR longitudinal and transverse relaxation times have been measure
d as a function of temperature at 300 and 500 MHz for aqueous solution
s of diblock and triblock copolymers of ethylene oxide (E) and 1,2-but
ylene oxide (B), encompassing micellar sol and gel phases. At the phas
e transitions from a micelle to a gel structure, transitions were obse
rved in the relaxation times of the E block, consistent with gel forma
tion by close packing of micelles at a spacing determined by the therm
odynamic radius rather than the hydrodynamic radius. Transient nuclear
Overhauser effects indicated that in the micelles there was considera
ble interpenetration of the E and B blocks at the core/fringe boundary
. The relaxation times were analysed using a two-step correlation func
tion. For the E block, the fast correlation time representing local se
gmental motions was little affected by gelation, whereas the slow corr
elation time representing larger-scale motions was much more affected.
Towards the lowest temperatures studied (<10 degrees C), the relaxati
on times of the B block indicated incipient micelle dissociation.