Mode Analysis of NMR Relaxation in a Polymer Melt

Hofmann, M.

doi:10.1021/acs.macromol.8b01189

Cited by 3 publications

(2 citation statements)

References 62 publications

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“…To obtain an overview of the diffusional behavior, we also calculated the dynamics (diffusion) [ 100 , 103 ] of the PDMS chains (from the MSD of all atoms in a chain) for all the systems studied and depicted in Figure 7 . It is worth noting that the calculated PDMS diffusion coefficient in the neutral melt, for

(

3 k), is

/s at 375 K, which is of the same order as the experimentally measured, by the pulse field gradient-NMR technique, diffusion coefficient of PDMS chains (

3.5 k),

/s at 323 K [ 44 ]. It is also noted that the ionic charges, on the polymer chain, hinder the PDMS chain dynamics (and thus diffusion); thus the chains, at all temperatures, in the neutral melt diffuse faster.…”

Section: Resultsmentioning

confidence: 76%

“…In particular, end-linked PDMS melts, using carboxyl ionomers [ 43 , 44 , 45 ], reinforced with gallium trivalent cationic counterions have been studied with respect to their mechanical behavior and swelling properties [ 11 ]. The morphology and rheology of PDMS ionomers with a varying number of ions per chain, and as a function of the cation type, have been investigated by means of small angle X-ray scattering and scanning electron microscopy techniques.…”

Section: Introductionmentioning

confidence: 99%

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Structure and Diffusion of Ionic PDMS Melts

2022

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Ionic polymers exhibit mechanical properties that can be widely tuned upon selectively charging them. However, the correlated structural and dynamical properties underlying the microscopic mechanism remain largely unexplored. Here, we investigate, for the first time, the structure and diffusion of randomly and end-functionalized ionic poly(dimethylsiloxane) (PDMS) melts with negatively charged bromide counterions, by means of atomistic molecular dynamics using a united atom model. In particular, we find that the density of the ionic PDMS melts exceeds the one of their neutral counterpart and increases as the charge density increases. The counterions are condensed to the cationic part of end-functionalized cationic PDMS chains, especially for the higher molecular weights, leading to a slow diffusion inside the melt; the counterions are also correlated more strongly to each other for the end-functionalized PDMS. Temperature has a weak effect on the counterion structure and leads to an Arrhenius type of behavior for the counterion diffusion coefficient. In addition, the charge density of PDMS chains enhances the diffusion of counterions especially at higher temperatures, but hinders PDMS chain dynamics. Neutral PDMS chains are shown to exhibit faster dynamics (diffusion) than ionic PDMS chains. These findings contribute to the theoretical description of the correlations between structure and dynamical properties of ion-containing polymers.

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(

3 k), is

/s at 375 K, which is of the same order as the experimentally measured, by the pulse field gradient-NMR technique, diffusion coefficient of PDMS chains (

3.5 k),

Section: Resultsmentioning

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Structure and Diffusion of Ionic PDMS Melts

2022

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Nuclear spin relaxation

Kowalewski¹

2020

Nuclear Magnetic Resonance

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The review covers the progress in the field of NMR relaxation in fluids primarily during 2019. Since the topic is returning to this volume SPR after a break of a few years, some highlights of the relaxation literature from the period 2014–18 are mentioned. The emphasis is on comparatively simple liquids and solutions of physico-chemical and chemical interest, as in previous periods, but selected biophysics-related topics (including some work on relaxation in solid biomaterials) and relaxation-related studies on more complex systems (macromolecular solutions, liquid crystalline systems, glassy and porous materials) are also covered. Section 2 of the chapter is concerned with general, physical and experimental aspects of nuclear spin relaxation, while Section 3 is concentrated on applications.

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Dynamics of Polymer Systems Studied by NMR Field-cycling Relaxometry

Hofmann

Flämig

Rössler

2019

NMR Methods for Characterization of Synthetic and Natural Polymers

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With the availability of commercial field-cycling (FC) relaxometers together with progress of home-built instruments, NMR relaxometry has gained new impetus as a method of investigating the dynamics in polymer systems. The FC method provides the dispersion of the spin–lattice relaxation rate. Transforming the relaxation data to the susceptibility representation and assuming frequency-temperature superposition master curves are constructed from individual relaxation spectra measured at different temperatures. Thereby, relaxation spectra covering up to ten decades in amplitude and frequency are obtained, which allow transformation into time correlation functions. In the case of protons, due to the intra- and intermolecular origin of dipolar interactions, spin–lattice relaxation dispersion reflects segmental rotation as well as translation. The latter displays a universal low frequencies dispersion law, which allows determining the diffusion coefficient in addition to the reorientational time constant. By singling out the intermolecular relaxation via isotope dilution experiments, sub-diffusive translation in terms of the mean-square displacement as a function of time is accessed. Likewise, information on reorientational dynamics is provided by the intramolecular relaxation. The results complement those of neutron scattering and rheological experiments. All in all, thorough testing of current polymer theories becomes possible and FC NMR relaxometry may become a method of molecular rheology.

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Mode Analysis of NMR Relaxation in a Polymer Melt

Cited by 3 publications

References 62 publications

Structure and Diffusion of Ionic PDMS Melts

Structure and Diffusion of Ionic PDMS Melts

Nuclear spin relaxation

Dynamics of Polymer Systems Studied by NMR Field-cycling Relaxometry

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