Acoustically Stimulated NMR Relaxometry Studies in Thermotropic Liquid Crystals

E. ANOARDO; F. BONETTO; J. A. REVELLI; R. KIMMICH

Torino, Italia

Conferencia; 4th Conference on Field Cycling NMR relaxometry; 2005

Universidad de Torino, Italia

The study of NMR relaxation in the presence of sonication can be used to display new features of the underlying molecular dynamics. In this context, liquid crystals are particularly interesting due to their relative molecular simplicity and observable couplings between the director and acoustic fields [1-3]. A strong coupling between the sonic field and order director fluctuations (ODF) exist trough density modulation across the sample volume [4]. The frequency spectrum of the hydrodynamic modes corresponding to the collective dynamics can be modified through the ultrasonic field, while the observation of these processes can be conveniently performed in a broad dynamical range. This experiment can conveniently be implemented through field-cycling NMR relaxometry [1,5-8], thus allowing to extend the study into the kHz Larmor frequency range, where ODF´s can be better observed through the proton spin-lattice relaxation time T1 [9]. The topic will be revisited and new physical insights will be discussed. REFERENCES 1- F. Bonetto, E. Anoardo and R. Kimmich, Chem. Phys. Lett. 361, 237 (2002).  2- J. V. Selinger, M. S. Spector, V. A. Greanya, B. T. Weslowski, D. K. Shenov and R.Shashidhar, Phys. Rev. E66, 051708 (2002). 3- A. P. Malanoski, V. A. Greanya, B. T. Weslowski, M. S. Spector, J. V. Selinger and R. Shashidhar, Phys. Rev. E69, 021705 (2004). 4- S. Nagai, P. Martinoty and S. Candau, J. Phys. 37, 769 (1976).  5- F. Bonetto, E. Anoardo and R. Kimmich, J. Chem. Phys. 118, 9037 (2003). 6- E. Anoardo, F. Bonetto and R. Kimmich, Phys. Rev. E68, 022701 (2003). 7- F. Bonetto and E. Anoardo, Phys. Rev. E68, 021703 (2003). 8- F. Bonetto and E. Anoardo, J. Phys. Chem. 121, 554 (2004). 9- W. Wölfel, F. Noack, M. Stohrer, Z. Naturforsh. 30a, 437 (1975).