Self-diffusion in the isotropic and mesomorphic states of the lanthanide-containing system based on nonionic surfactant according to the NMR data

Abstract

Molecular self organization in a system based on lanthanum nitrate and the nonionogenic surfactant, viz., decaethylene glycol monododecyl ether, was studied in an aqueous solution and in the liquid crystalline state. Molecular motion and phase transitions in the system were characterized by the high resolution pulsed gradient spin echo 1 H NMR method.Considerable attention is presently given to studies of the structural and phase properties of lyotropic liquid crystals (LLC). 1-5 Metal containing LLC are widely used in the template synthesis of nanomaterials, as well as in biotechnology, nanocatalysis, and molecular optoelec tronics. 6-12 Lanthanides having unique physical proper ties are of special significance among the metals under study. 13 The Eu 3+ , Tr 3+ , and Tm 3+ ions manifest intense photo and electroluminescence in different spectral re gions. Inclusion of these ions in the structure of a liquid crystal (LC) allows the ions to be potentially used in LC displays as luminescent materials. 14 Some trivalent lan thanide ions are paramagnetics possessing high magnetic moments and magnetic susceptibility anisotropy, which provides their orientation in magnetic field. 15 In some systems, lanthanide ions exhibit strong catalytic ef fects. 16,17 However, despite increased interest in lyotro pic metallomesogens, the number of works devoted to the lanthanide containing lyotropic systems is rather re stricted. 18-21Considerable part of mesomorphic lyophases repre sent supramolecular associates based on spherical, cylin drical, or plate like micelles formed by surfactant (Surf) molecules. Their phase state and behavior are determined to a great extent by the structure of these structural units. Therefore, in the context of studying the properties of LLC, certain attention is given to the examination of micellar self organization of surfactant molecules. 22-24 The NMR method in different modifications is very informative for investigation of the structure and phase transformations of micellar systems and meso phases. 25-28 We have earlier 21 determined the critical micelle concentrations (CMC), identified the hexagonal type of the mesophase, and constructed the isobaric phase diagrams for binary (C 12 EO 10 -H 2 O) and ternary (C 12 EO 10 -Lа(NO 3 ) 3 •6H 2 O-H 2 O) systems containing decaethylene glycol monododecyl ether (C 12 EO 10 ). This work continues the studies of the lanthanide containing LLC and is devoted to the study of molecular motion in a micellar solution and in the LC state by high resolution pulsed gradient spin echo 1 H NMR spectroscopy. ExperimentalCommercial decaethylene glycol monododecyl ether C 12 H 25 O(CH 2 CH 2 O) 10 H (C 12 EO 10 ) and lanthanum nitrate hexa hydrate Lа(NO 3 ) 3 •6H 2 O (La III ) (Aldrich) were used. Mi cellar solutions were prepared using bidistilled water, and the C 12 EO 10 -Ln(NO 3 ) 3 •6H 2 O molar ratio was maintained constant and equal to 0.5. The micellar solutions were studied in a concen tration range of 10 -5 -10 -1 mol L -1 at the temperature 298 K. A С 12 EO ...

Lyotropic La-containing lamellar liquid crystals: phase behaviour, thermal and structural properties

“…Despite increased interest in lyotropic metallomesogens, there is rather limited number of studies dedicated to lanthanidecontaining lyotropic phases. [24][25][26][27][28] The present study continues our research on the synthesis and characterization of lanthanidecontaining lyotropic liquid crystals based on oxyethylated surfactants. This work is aimed at finding a correlation between the molecular structure of amphiphilic molecules and supramolecular organization in the mesophases containing a lanthanide ion.…”

Mesogenic and Luminescent Properties of Lyotropic Liquid Crystals Containing Eu(III) and Tb(III) Ions

“…In our earlier papers, we first discussed synthesis of lanthanide containing LLC systems, based on nonionic surfactants made up of decaethylene glycol monododecyl ether and tetraethylene glycol monododecyl ether, which are stable over a wide range of temperatures (including room temperature) and concentrations. Self-organizing processes in solutions and mesophases were investigated. − It was shown that the luminescence efficiency depends on the liquid crystal phase orientation. The luminescence efficiency demonstrated a 7-fold increase when a transition from unoriented samples to oriented samples occurred .…”