Type A versus Type B Glass Formers:  NMR Relaxation in Bulk and Confining Geometry

Lusceac, S. A.; Koplin, Christof; Medick, P.; Vogel, Michael; Brodie–Linder, Nancy; LeQuellec, C.; Alba-Simionesco, C.; Rössler, E. A.

doi:10.1021/jp040376p

Cited by 44 publications

(45 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…͑8͒, we obtain a stretching parameter ␤ = 0.48 ͑see Fig. 30,47 In the literature, 30,46 it was demonstrated that nonexponential 2 H spin-lattice relaxation is due to a distribution of spin-lattice relaxation times, V͑T 1 ͒. For the studied polymer electrolytes PPO-LiClO 4 , including the compositions 15:1 and 30:1, which were measured at a Larmor frequency 0 / ͑2͒ = 76.8 MHz, we find stretching parameters in the range of 0.4ഛ ␤ ഛ 0.6 at temperatures somewhat above T g .…”

Section: -4mentioning

confidence: 99%

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis

Vogel

Torbrügge

2006

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

We investigate ion and polymer dynamics in polymer electrolytes PPO-LiClO4 performing 2H and 7Li NMR line-shape analysis. Comparison of temperature dependent 7Li and 2H NMR spectra gives evidence for a coupling of ion and polymer dynamics. 2H NMR spectra for various salt concentrations reveal a strong slowdown of the polymer segmental motion when the salt content is increased. The 2H NMR line shape further indicates that the segmental motion is governed by dynamical heterogeneities. While the width of the distribution of correlation times G(log tau) is moderate for low and high salt content, an extremely broad distribution exists for an intermediate salt concentration of 15:1 PPO-LiClO4. For the latter composition, a weighted superposition of two spectral components, reflecting the fast and the slow polymer segments of the distribution, describes the 2H NMR line shape over a broad temperature range. Analysis of the temperature dependent relative intensity of both spectral components indicates the existence of a continuous rather than a discontinuous distribution G(log tau). Such continuous distribution is consistent with gradual fluctuations of the local salt concentration and, hence, of the local environments of the polymer segments, whereas it is at variance with the existence of large salt-depleted and salt-rich domains featuring fast and slow polymer dynamics, respectively. Finally, for all studied PPO-LiClO4 mixtures, the 2H NMR line shape strongly depends on the echo delay in the applied echo-pulse sequence, indicating that the structural relaxation of the polymer segments involves successive rotational jumps about small angles gamma < 20 degrees .

show abstract

Section: -4mentioning

confidence: 99%

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis

Vogel

Torbrügge

2006

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

show abstract

“…2 In addition to a shift in T g , the distribution of correlation times, G(ln τ), is significantly broadened. [3][4][5] Hence, one wonders if discussing some global or averaged property like T g or a single correlation time is an appropriate way to describe the change of the dynamics occurring in confinement. Addressing this problem, most detailed information has been gained from molecular dynamics (MD) simulations.…”

Section: Introductionmentioning

confidence: 99%

Glassy Dynamics in Nanoconfinement as Revealed by ³¹P NMR

2009

Self Cite

View full text Add to dashboard Cite

We investigated the glass former m-tricresyl-phosphate confined in different nanoporous silica matrices with defined pore radii from 2-150 nm. While applying different 31P NMR techniques, we were able to detect the extremely stretched correlation functions extending over 7-8 decades in time and reflecting strong dynamic heterogeneities. The experimental results were explained by a topological model for which the broad distribution of correlation times G(ln tau) becomes inhomogeneous in space; that is, the "local" dynamics given by a correlation time tau(r) depend on the distance from the pore center. As tau(r) changes with temperature, we were able to reintroduce the idea of a dynamic correlation length.

show abstract

“…[25][26][27][28] Traditionally, 2 H NMR spectroscopy is used as a powerful technique for the study of dynamics in glassy systems, liquid crystals, and polymers, with the emphasis being on structural phase and glass transitions of essentially amorphous systems. 25,26,[29][30][31][32][33][34][35] In addition, 2 H NMR in conjunction with neutron scattering afforded a better understanding of the cross-link between structural and dynamic phenomena and provided new insights into relaxation and tunneling processes [36][37][38][39] in simple crystalline salts, among which ammonium compounds such as NH 4 Cl 40-43 or (NH 4 ) 2 SO 4 play a prominent role. Accordingly, applying the 2 H NMR technique to the in situ study of the topochemical transformation of ammonium dicyanamide into dicyandiamide seems to be a straightforward issue, which will be discussed in some detail in the present work.…”

Section: Introductionmentioning

confidence: 99%

Reorientational Dynamics and Solid-Phase Transformation of Ammonium Dicyanamide into Dicyandiamide: A ²H Solid-State NMR Study

et al. 2007

View full text Add to dashboard Cite

The reorientational dynamics of ammonium dicyanamide ND 4 [N(CtN) 2 ] and the kinetics as well as the mechanism of the solid-state isomerization reaction from ammonium dicyanamide into dicyandiamide (Nt CsNdC(NH 2 ) 2 ) was studied by means of 2 H and 14 N solid-state NMR spectroscopy in a temperature range between 38 and 390 K. Whereas in previous investigations the mechanism of the solid-state transformation was investigated by means of vibrational and magic angle spinning solid-state NMR spectroscopy as well as neutron diffraction, we here present a comprehensive 2 H study of the ammonium ion dynamics prior to and during the course of the reaction, thereby highlighting possible cross correlations between dynamics and reactivity involving the ammonium ion. The ND 4 + group was found to undergo thermally activated random jumps in a tetrahedral potential, which is increasingly distorted with increasing temperature, giving rise to an asymmetrically compressed or elongated tetrahedron with deviations from the tetrahedral angle of up to 6°. The correlation time follows an Arrhenius law with an activation energy of E a ) 25.8(2) kJ mol -1 and an attempt frequency of τ 0 -1 ) 440(80) THz. The spin-lattice relaxation times were fitted according to a simple Bloembergen-Purcell-Pound type model with a T 1 minimum of 4 ms at 230 K. Temperature-dependent librational amplitudes were extracted by line-shape simulations between 38 and 390 K and contrasted with those obtained by neutron diffraction, their values ranging between 5 and 28°. The onset and progress of the solid-phase transformation were followed in situ at temperatures above 372 K and could be classified as a strongly temperature-dependent, heterogeneous two-step reaction proceeding with rapid evolution of ammonia and comparatively slow subsequent reintegration into the solid. On the microscopic level, this correlates with a rapid proton transferspossibly triggered by a coupling between the ammonium ion dynamics and phonon modes on the terahertz time scalesand an essentially decoupled nucleophilic attack of ammonia at the nitrile carbon, giving rise to significantly differing time constants for the two processes.

show abstract

Type A versus Type B Glass Formers: NMR Relaxation in Bulk and Confining Geometry

Cited by 44 publications

References 25 publications

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis

Glassy Dynamics in Nanoconfinement as Revealed by ³¹P NMR

Reorientational Dynamics and Solid-Phase Transformation of Ammonium Dicyanamide into Dicyandiamide: A ²H Solid-State NMR Study

Contact Info

Product

Resources

About

Type A versus Type B Glass Formers: NMR Relaxation in Bulk and Confining Geometry

Cited by 44 publications

References 25 publications

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis

Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis

Glassy Dynamics in Nanoconfinement as Revealed by 31P NMR

Reorientational Dynamics and Solid-Phase Transformation of Ammonium Dicyanamide into Dicyandiamide: A 2H Solid-State NMR Study

Contact Info

Product

Resources

About

Glassy Dynamics in Nanoconfinement as Revealed by ³¹P NMR

Reorientational Dynamics and Solid-Phase Transformation of Ammonium Dicyanamide into Dicyandiamide: A ²H Solid-State NMR Study