title: (1)H NMR Relaxometric Study of Molecular Dynamics in a "de Vries" Liquid Crystal.
abstract: Liquid crystals that exhibit de Vries smectic A phases are promising materials for new generations of ferroelectric liquid crystal displays and other electro-optical devices. We investigated the molecular dynamic properties of a rod-like de Vries liquid crystal compound, namely the 9HL, a (S)-hexyl lactate derivative, in the whole mesophasic range. This is the first molecular dynamics' investigation on a de Vries phase, and the interest of this system is related to the understanding of the structural and supramolecular organization of de Vries SmA phases, which has been a subject of a broad scientific debate in the last years. Proton NMR spin-lattice relaxation times, T1, were measured in the range 100 MHz to 5 kHz, thus covering a very wide range of motional regimes. (1)H NMR dispersion curves and temperature-dependent relaxation rates were analyzed with a global minimum target fitting approach and the main molecular motions, namely reorientational diffusion, translational self-diffusion, layer undulation, and tilting director fluctuations were fully characterized. The molecular dynamics' behavior observed across the SmA-SmC* phase transitions of 9HL was consistent with the proposed cluster diffuse cone model for the de Vries SmA phase.
authors.affiliation: Jožef Stefan Institute , Jamova 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Anton
authors.initials: A
authors.lastname: Gradišek
authors.affiliation: Dipartimento di Chimica e Chimica Industriale , via Moruzzi 13, 56124 Pisa, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Domenici
authors.affiliation: Jožef Stefan Institute , Jamova 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Tomaž
authors.initials: T
authors.lastname: Apih
authors.affiliation: Institute of Physics, Academy of Sciences of the Czech Republic , Na Slovance 2, 182 21 Prague, Czech Republic.
authors.forename: Vladimíra
authors.initials: V
authors.lastname: Novotná
authors.affiliation: Center of Physics and Engineering of Advanced Materials, Instituto Superior Técnico, Universidade de Lisboa , Av. Rovisco Pais, 1049-001 Lisboa, Portugal.|Department of Physics, Instituto Superior Técnico, Universidade de Lisboa , Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Sebastião