Evidence for NMR Relaxation Enhancement in a Protic Ionic Liquid by the Movement of Protons Independent of the Translational Diffusion of Cations.

The molecular dynamics, thermal stability, and ionic conductivity were studied in the protic ionic liquid 1-methylimidazolium bis(trifluoromethylsulfonyl)imide ([MIm][TFSI]). The relaxation of the 1H spin-lattice of cations in the measured frequency range (10 kHz to 20 MHz) and temperature (298 to 343 K) is sensitive mainly to slow processes occurring in the molecular dynamics of protic ionic liquid and dominated by the contribution of intermolecular translational diffusion. Molecular rotations give only a constant contribution and become significant in the higher frequency range. An interesting feature is the observed enhancement of the 1H spin-lattice relaxation below 0.03 MHz attributed to the exchange of protons (order of 10-5 s) between imidazolium cations. The measurements of the self-diffusion coefficient of hydrogen atoms of cation from 298 to 343 K additionally confirm the observed phenomenon. The coefficient for exchangeable protons -NH is higher than for the cation. The nuclear magnetic resonance (NMR) experiments provide unambiguous evidence for proton transport decoupled from molecular diffusion of ions and support the conclusion that the charge transport mechanism in the studied PIL includes contributions from both the vehicular and Grotthus mechanisms. The protic ionic liquid is thermally stable to about 573 K as shown by thermogravimetric analysis and its electrical conductivity is 5 × 10-2 S/cm at 423 K.

Detection of Authenticity and Quality of the Turkish Delights (Lokum) by Means of Conventional and Fast Field Cycling Nuclear Magnetic Resonance Relaxometry.

Turkish delights (lokum) are traditional confectionery products that contain mainly sucrose as the sugar source and starch as the gelling agent. However, manufacturers sometimes might prefer to use corn syrup instead of sucrose to decrease the cost. This jeopardizes the originality of Turkish delights and leads to production of adulterated samples. In this study, Turkish delights were formulated using sucrose (original sample) and different types of corn syrups (SBF10, SCG40, and SCG60). Results clearly indicated that corn-syrup-containing samples had improved textural properties and were less prone to crystallization. However, this case affected authenticity of the products negatively. Both time domain nuclear magnetic resonance (TD NMR) and fast field cycling nuclear magnetic resonance (FFC NMR) techniques were found to be effective to discriminate the original samples from the corn-syrup-containing samples. In addition, quantitative analysis of FFC NMR showed that, apart from the rotational motions, molecules in Turkish delights (mainly water and also sugar molecules) undergo two types of translational dynamics.

NMR studies of molecular ordering and molecular dynamics in a chiral liquid crystal with the SmC_{α}

Molecular dynamics of the antiferroelectric liquid crystal 4'-(octyloxy)biphenyl-4-carboxylate2-fluoro-4-[(octyl-2-yloxy)carbonyl]phenyl (abbreviated as D16) was investigated using different nuclear magnetic resonance (NMR) techniques. D16 molecules form a smectic-C_{α}^{*} phase (SmC_{α}^{*}) in an extremely wide temperature range (∼10 °C). Due to a small tilt of the molecules, this phase is characterized by short switching times, important for new photonic applications. The proton spin-lattice relaxation times were measured in isotropic (Iso), smectic-A (SmA), and SmC_{α}^{*} phases over a wide frequency range of five decades, with conventional and fast field-cycling NMR techniques. This approach allowed a comparison of the essential processes of molecular dynamics taking place in these phases. On the basis of NMR relaxometry measurements, we present a description of the motional behavior of liquid crystal molecules forming SmC_{α}^{*}. Pretransitional effects were observed in wide temperature ranges in both the isotropic and SmA phases in D16. The ^{1}H fast field-cycling NMR measurements were supplemented with NMR diffusometry and ^{19}F NMR spectroscopy.

Effect of polymer network on thermodynamic stability and switching behavior of the smectic-C_{α}

A polymer-stabilized liquid crystal based on 4^{'}-(octyloxy)biphenyl-4-carboxylate 2-fluoro-4-((octyl-2-yloxy)carbonyl)phenyl (D16) and 1,6 hexanediol diacrylate as a monomer was prepared by in situ photopolymerization. The selected antiferroelectric liquid crystal contains a fast-switching smectic C_{α}^{*} phase (SmC_{α}^{*}), and the influence of the polymer network on the thermodynamic stability of this phase and its switching behavior under applying time-dependent electric field were studied. Using dielectric spectroscopy and polarizing microscopy, the liquid crystal materials were characterized, and subsequently with the use of the reversal current method (RCM) the current response, especially from the SmC_{α}^{*} phase was carefully analyzed. The current response is complex and also depends on the neighboring liquid crystal phases. In the liquid crystal-polymer system, as well as in the liquid crystal-monomer mixture, a significant shift of the temperature range of the SmC_{α}^{*} phase toward lower temperatures was observed; however, the thermodynamic instability related to the transformation to the crystalline phase was also noted and characterized. Because of the fuzzy phase transitions detected in the liquid crystal-polymer system by dielectric spectroscopy and also because of the lack of the characteristic dielectric signature of SmC_{α}^{*} after polymerization, we proposed the use of the RCM, as a complementary one, to identify the SmC_{α}^{*} phase even in such complex materials.