U Tracht | PubMed Health

PubMed1999

Combined reduced 4D 13C exchange and 1H spin diffusion experiment for determining the length scale of dynamic heterogeneities.

A multidimensional static solid-state NMR experiment is described that combines 13C exchange sequences with 1H spin diffusion. It realizes a spatial correlation of different reorientation rates. By means of this experiment the length scale of dynamic heterogeneities can be measured directly. The pulse sequence and phase cycle as well as the experimental setup procedure and data analysis are described in detail. It complements the previous letter on this subject where a brief report of the main results were presented (U. Tracht et al., 1998, Phys. Rev. Lett. 81, 2727). Application of this experiment to an amorphous polymer in the supercooled state yields a length scale of immobile regions of about 3 nm.

Magnetic Resonance Spectroscopy↗

PubMed1998

2D CP/MAS 13C isotropic chemical shift correlation established by 1H spin diffusion.

A new 2D solid-state CP/MAS 13C NMR exchange experiment for through-space isotropic chemical shift correlation is proposed and demonstrated. Through-space correlation is established via a second cross polarization from 13C to 1H and subsequent 1H spin diffusion. A third cross polarization results in the final 13C-13C isotropic chemical shift correlation. The 1H spin diffusion time is a variable parameter allowing different mean square magnetization displacements to be probed. Experimental results on mixtures of differently 13C-labeled alanine and polyethylene indicate that this site-selective 2D technique can be used to characterize domain sizes and proximities over a wide range of length scales (1-200 nm) in solids such as polymers or biological materials.

Alanine↗

PubMed1998

Erratum to "23Na solid state MAS NMR of sodium halides occluded in zeolites".

Occlusion of sodium chloride and sodium bromide in zeolitic pores was performed by heating mixtures of the salts with zeolites NaY and NaA under high vacuum conditions. The obtained samples were subjected to various further pretreatments like washing with water and zinc-exchange, and were investigated spectroscopically with the 23Na MAS NMR technique at various Zeeman field strengths. In the case of NaY, the halides are occluded in both types of cages of the faujasite structure. About 90% of the sodalite cages are shown to have incorporated salt which is concluded to be part of [Na4Hal]3+ clusters as in the case of sodalite type materials.

Bromides↗

PubMed1997

23Na solid state MAS NMR of sodium halides occluded in zeolites.

Occlusion of sodium chloride and sodium bromide in zeolitic pores was performed by heating mixtures of the salts with zeolites NaY and NaA under high vacuum conditions. The obtained samples were subjected to various further pretreatments like washing with water and zinc-exchange, and were investigated spectroscopically with the 23Na MAS NMR technique at various Zeeman field strengths. In the case of NaY, the halides are occluded in both types of cages of the faujasite structure. About 90% of the sodalite cages are shown to have incorporated salt which is concluded to be part of [Na4Hal]3+ clusters as in the case of sodalite type materials.

Bromides↗