Intermolecular Spin Relaxation and Translation Diffusion in Liquids and Polymer Melts: Insight from Field‐Cycling¹H NMR Relaxometry

Abstract

With the advent of commercial field-cycling (FC) spectrometers, NMR relaxometry has gained new momentum as a method of investigating dynamics in liquids and polymers. The outcome of FC NMR experiments is spin-lattice relaxation time versus frequency (relaxation dispersion). In the case of protons, due to the intra- and intermolecular origin of dipolar interactions, the relaxation dispersion reflects rotational as well as translational dynamics. The latter shows a universal dispersion law at low frequencies, which allows determination of the diffusion coefficient D(T) in addition to the rotational correlation time τ(rot)(T), that is, FC (1)H NMR becomes an alternative to field-gradient NMR spectroscopy. Subdiffusive translation found in polymers can be accessed by singling out the intermolecular relaxation through isotope dilution experiments, and the mean square displacement can then be revealed as a function of time, thus complementing neutron scattering experiments. Likewise, information on reorientational dynamics is provided by the intramolecular relaxation. Assuming frequency-temperature superposition the corresponding correlation functions can be monitored up to eight decades in amplitude and time, which allows thorough testing of current polymer theories.

Proton spin dynamics in polymer melts: New perspectives for experimental investigations of polymer dynamics

“…Indeed, as anticipated above, it has been shown that the intermolecular contribution to R 1 (ω) must not be ignored suggesting that the exponent α might also be influenced by the intermolecular relaxation [13,16,17,25]. Moreover, the intermolecular relaxation is an important source of information regarding translational dynamics in polymer melts.…”

“…As a continuation of the pioneering work of Kimmich and collaborators [7] the dynamics of linear polymers such as 1,4-polybutadiene (PB) with different M has been studied by field-cycling (FC) 1 H NMR relaxometry [13,15,19,24,[55][56]. Transforming the measured relaxation rates Applying FTS the correlation loss is probed over nine decades in time and eight in amplitude.…”

“…The dynamics of the investigated systems is mainly reflected through characteristic features of nuclear spin relaxations. Important findings of recent years [7,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], affecting the understanding of the proton spin dynamics in polymer melts are the subject of discussion of this paper.…”

Translational dynamics of ionic liquid imidazolium cations at solid/liquid interface in gel polymer electrolyte

“…The pulsed and static field gradient NMR techniques can be classified as direct ones because the diffusion coefficients are determined directly from the NMR signal attenuation, recorded as a function of the magnetic field gradient strength and/or the time at which the diffusion is followed. Recently, the fast field-cycling (FFC) NMR relaxometry technique has been also successfully used for characterization of the translational diffusion, especially in liquid and soft systems [4,26,27,31,32]. This indirect and non-gradient method gives the possibility to determine the diffusion coefficient from measured frequency dependency (dispersion profile) of spin-lattice relaxation time by applying a suitable theoretical model describing the dynamics of the molecules (ions).…”

“…Translational dynamics of particles (molecules or ions) has fundamental meaning for all important transport processes occurring in micro-scale in nature and therefore is extensively explored in different molecular systems [1][2][3][4]. For ionic liquids (ILs), the translational modes of the molecular dynamics of ions potentially provide the information on interionic interactions or molecular rearrangements reflecting complex diffusion processes associated, among others, directly with ionic conductivity [5][6][7].…”