Solid-State NMR and Impedance Spectroscopy Study of Spin Dynamics in Proton-Conducting Polymers: An Application of Anisotropic Relaxing Model

Abstract

The 1 H− 13 C cross-polarization (CP) kinetics in poly [2-(methacryloyloxy)ethyltrimethylammonium chloride] (PME-TAC) was studied under moderate (10 kHz) magic-angle spinning (MAS). To elucidate the role of adsorbed water in spin diffusion and proton conductivity, PMETAC was degassed under vacuum. The CP MAS results were processed by applying the anisotropic Naito and McDowell spin dynamics model, which includes the complete scheme of the rotating frame spin−lattice relaxation pathways. Some earlier studied proton-conducting and nonconducting polymers were added to the analysis in order to prove the capability of the used approach and to get more general conclusions. The spin-diffusion rate constant, which describes the damping of the coherences, was found to be strongly depending on the dipolar I−S coupling constant (D IS ). The spin diffusion, associated with the incoherent thermal equilibration with the bath, was found to be most probably independent of D IS . It was deduced that the drying scarcely influences the spin-diffusion rates; however, it significantly (1 order of magnitude) reduces the rotating frame spin−lattice relaxation times. The drying causes the polymer hardening that reflects the changes of the local order parameters. The impedance spectroscopy was applied to study proton conductivity. The activation energies for dielectric relaxation and proton conductivity were determined, and the vehicle-type conductivity mechanism was accepted. The spin-diffusion processes occur on the microsecond scale and are one order faster than the dielectric relaxation. The possibility to determine the proton location in the H-bonded structures in powders using CP MAS technique is discussed.

Step-by-step from amorphous phosphate to nano-structured calcium hydroxyapatite: monitoring by solid-state 1H and 31P NMR and spin dynamics

“…The slowdown of the relaxation of 31 P spins (T S 1r -N) is seen in the composite sample and nano-CaHA (Table 1). This behavior of the spin-lattice relaxation times in the rotating frame (T I 1r and T S 1r ) is very similar to that observed in some polymers 40 -the higher content of structured water (Fig. 5), i.e.…”

Solid-state NMR study of spin dynamics and local disorder in smart polymers: PDMAEMA

“…( 6)). obtained for PDMAEMA were compared with those for PMETAC, which is the quaternized derivative of PDMAEMA [8].…”

“…Unfortunately, there are strong overlaps of the CH 2 main chain signal with the neighbouring N-CH 2 peak in PDMAEMA (57 and 59 ppm, respectively (Fig. 1)) and that with the quaternary carbon (q) peak in PMETAC (46.5 and 45 ppm, see [8]). The signals can be separated applying the standard computing routines.…”

“…4). Note that the local order around the N + -CH 2 site in PMETAC is characterized by S = 0.91 that is intrinsic for quite rigid molecular systems [8,[33][34][35]. Hereby it is intriguing to compare the dynamic behaviour and disorder of the main chains.…”

“…the consideration of the time evolution (contact time) of communication between spins, provides the rates of spin-diffusion and spin-lattice relaxation, the profiles of distribution of dipolar coupling and some other parameters accounting for the effective sizes of spin clusters [4][5][6]. Hence, it is a powerful method studying fine structural details and dynamics in advanced complex materials and polymers among those [7][8][9][10].…”