Diffusion spectrum of polymer melt measured by varying magnetic field gradient pulse width in PGSE NMR

Mohorič, Aleš (author), Lahajnar, Gojmir (author), Stepišnik, Janez (author)

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.

• Language: English
• Keywords: nuclear magnetic resonance, diffusion, polymer melts, PGSE method, NMR, Rouse, reptation
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FMF - Faculty of Mathematics and Physics
• Publication status: Published
• Publication version: Version of Record
• Year: 2020
• Number of pages: 10 str.
• Numbering: Vol. 25, iss. 24, art. 5813
• PID: 20.500.12556/RUL-134851
• UDC: 543.429.23
• ISSN on article: 1420-3049
• DOI: 10.3390/molecules25245813
• COBISS.SI-ID: 42641411
• Publication date in RUL: 04.02.2022

Record is a part of a journal

• Title: Molecules
• Shortened title: Molecules
• Publisher: MDPI
• ISSN: 1420-3049
• COBISS.SI-ID: 18462981

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.
• Licensing start date: 09.12.2020

Secondary language

• Language: Slovenian
• Keywords: jedrska magnetna resonanca, difuzija, taline polimerov, metoda PGSE

Projects

• Funder: ARRS - Slovenian Research Agency
• Project number: P1-0060
• Name: Eksperimentalna biofizika kompleksnih sistemov in slikanje v biomedicini