20.500.12556/RUL-134851 Diffusion spectrum of polymer melt measured by varying magnetic field gradient pulse width in PGSE NMR The translational motion of polymers is a complex process and has a big impact on polymer structure and chemical reactivity. The process can be described by the segment velocity autocorrelation function or its diffusion spectrum, which exhibit several characteristic features depending on the observational time scale—from the Brownian delta function on a large time scale, to complex details in a very short range. Several stepwise, more-complex models of translational dynamics thus exist—from the Rouse regime over reptation motion to a combination of reptation and tube-Rouse motion. Accordingly, different methods of measurement are applicable, from neutron scattering for very short times to optical methods for very long times. In the intermediate regime, nuclear magnetic resonance (NMR) is applicable—for microseconds, relaxometry, and for milliseconds, diffusometry. We used a variation of the established diffusometric method of pulsed gradient spin-echo NMR to measure the diffusion spectrum of a linear polyethylene melt by varying the gradient pulse width. We were able to determine the characteristic relaxation time of the first mode of the tube-Rouse motion. This result is a deviation from a Rouse model of polymer chain displacement at the crossover from a square-root to linear time dependence, indicating a new long-term diffusion regime in which the dynamics of the tube are also described by the Rouse model. nuclear magnetic resonance diffusion polymer melts PGSE method NMR Rouse reptation jedrska magnetna resonanca difuzija taline polimerov metoda PGSE true false true Angleški jezik Slovenski jezik Članek v reviji 2022-02-04 12:14:19 2022-02-04 12:14:22 2022-09-14 04:10:19 0000-00-00 00:00:00 2020 0 0 10 str. iss. 24, art. 5813 Vol. 25 Dec. 2020 0000-00-00 Zaloznikova Objavljeno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 543.429.23 1420-3049 10.3390/molecules25245813 42641411 RAZ_Mohoric_Ales_2020.pdf RAZ_Mohoric_Ales_2020.pdf 1 D2402BB155DD2F345710F8D02CFECF1D 44c25721bb91bbaadac71961f65e2880df9913d8a29d8dcaa006dff23106e72a 2d0d0e6e-85ad-11ec-abdb-00155dcfd717 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=153550 https://www.mdpi.com/1420-3049/25/24/5813 0 d3bb3415-85ab-11ec-abdb-00155dcfd717 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=153549 Fakulteta za matematiko in fiziko 0 0 0