NMR relaxation in supercooled di-methyl phthalate

Abstract

Spin-lattice relaxation times and nuclear Overhauser enhancement factors (NOE) for the individual ring carbons in di-methyl phthalate (DMF) were measured over a wide range of temperatures. The results show that the reorientational correlation function corresponding to the global dynamics in supercooled liquid can be well described by a Davidson-Cole distribution. The viscosity dependence of the reorientational correlation time derived is analysed to investigate the adequacy of the modified Debye equation to description of the microscopic behaviour of supercooled systems.

Nuclear magnetic relaxation study of carbon-13 in di-pentyl phthalate

“…The sample studied was custom synthesized. Its purity was checked using 1 H and 13 C high-resolution NMR spectra. The sample investigated was degassed by the freeze-pump-thaw technique and sealed under vacuum in a Pyrex tube which, then, was placed in a Wilmard 10 mm o.d.…”

“…The problem of side-chain dynamics has been the focus of considerable attention [1][2][3], and measurements of 13 C spin-lattice relaxation times and nuclear Overhauser enhancement (NOE) factors have proved to provide the basis of a versatile method for studying this problem for a variety of molecular systems, such as supercooled liquids, glasses, biomolecules, micelles, and polymers [4][5][6][7]. The understanding of global and local dynamical properties of these complex systems is of great relevance to basic aspects of theory and to many branches of materials sciences.…”

“…The understanding of global and local dynamical properties of these complex systems is of great relevance to basic aspects of theory and to many branches of materials sciences. In the present paper we use 13 C NMR techniques to study di-pentyl phthalate. The selection of the compound for the study was motivated by the fact that its simple molecular structure may allow us to understand how the transition from a fluid to a solid glass, which occurs gradually as a liquid is supercooled, affects different reorientational degrees of freedom.…”

“…While many NMR studies performed on supercooled liquids examine the coupling between translational and rotational motion [8], such studies on internal reorientations in flexible molecules are limited. We have studied the spin-lattice relaxation times T 1 and the NOE factors for DPP covering a temperature range between 227 and 356.8 K. When analysing the results obtained, we used the general expressions for the 13 C T 1 and NOE, which hold for the intramolecular dipolar relaxation mechanism on condition of complete proton decoupling [9]:…”

“…Although this simple model is successful in explaining the dynamics in non-viscous liquids, it usually does not account for experimental observations for more complex systems, where the dynamics cannot be described by an exponential correlation function or in terms of a single correlation time [12,13]. Therefore, when analysing the experimental results, we have also considered the spectral density functions assuming a distribution of reorientational correlation times of the form…”