Pulsed-Field-Gradient NMR Study of Anisotropic Molecular Translational Diffusion in nOCB Liquid Crystals
2013 (English)In: Applied Magnetic Resonance, ISSN 0937-9347, Vol. 44, no 1-2, 169-180 p.Article in journal (Refereed) Published
Pulsed-field-gradient nuclear magnetic resonance (NMR) combined with magic echo decoupling is applied to study anisotropic diffusion in samples with strong static dipolar spin interactions. The approach, due to its moderate demands on the NMR hardware, can be implemented on standard commercial equipment for routine diffusion studies of liquid crystals. Using a microimaging probe, measurement of diffusion in arbitrary spatial direction is possible. Hence, the principal components of the diffusion tensor are directly obtained. Anisotropic diffusion is investigated in the thermotropic mesophases of a homologous series of nOCB liquid crystals and an analogous compound with hydroxyl groups. The geometric average diffusion coefficient changes continuously at the isotropic-nematic phase transition. Experimental data are described in terms of the molecular translation models in the nematic phase and for the second-order nematic-smectic A phase transition. The diffusion anisotropy is higher for the sample with terminal hydroxyl groups suggesting significant molecular association via hydrogen bonding.
Place, publisher, year, edition, pages
2013. Vol. 44, no 1-2, 169-180 p.
Nuclear-Magnetic-Resonance, Solid-State Nmr, Self-Diffusion, Pgse Nmr, Pfg Nmr, Dynamics, Phase, Echo, Polysiloxane, Coefficients
IdentifiersURN: urn:nbn:se:kth:diva-117830DOI: 10.1007/s00723-012-0390-1ISI: 000313796500016ScopusID: 2-s2.0-84872672019OAI: oai:DiVA.org:kth-117830DiVA: diva2:603856
FunderSwedish Research Council
QC 201302072013-02-072013-02-052013-02-25Bibliographically approved