Orientational ordering from molecular polarizabilities and an odd-even effect in nCB homologous series

The molecular polarizabilities of the homologous series of cyano-alkyl-biphenyl (C _n H_2n+1.φφ.CN for n = 5 to 9) have been calculated using two different internal field models. From these values the orientational order parameters have been obtained. The orientational ordering exhibits an odd-even alteration along the series. The variations of different parameters with the increase of alkyl chain length are discussed. The relative stabilities of the alkyl-cyano-biphenyls are also discussed in terms of the molecular parameters.     

1H and 2H NMR studies of benzene confined in porous solids: melting point depression and pore size distribution

The pore size distributions of four controlled pore glasses and three silica gels with nominal diameters in the range 4-24 nm were determined by measuring the 1H and 2H NMR signals from the non-frozen fraction of confined benzene and perdeuterated benzene as a function of temperature, in steps of ca. 0.1-1 K. The liquid and solid components of the adsorbate were distinguished, on the basis of the spin-spin relaxation time T2, by employing a spin-echo sequence. The experimental intensity curves of the liquid component are well represented by a sum of two error functions. The mean melting point depression of benzene and perdeuterated benzene confined in the four controlled pore glasses, with pore radius R, follows the simplified Gibbs-Thompson equation DeltaT=kp/R with a kp value of 44 K nm. As expected, the kp value mainly determines the position of the pore size distribution curve, i.e., the mean pore radius, while the transition width determines the shape of the pore size distribution curve. The excellent agreement between the results from the 1H and 2H measurements shows that the effect of the background absorption from protons in physisorbed water and silanol groups is negligible under the experimental conditions used. The overall pore size distributions determined by NMR are in reasonable agreement with the results specified by the manufacturer, or measured by us using the N2 sorption technique. The NMR method, which is complementary to the conventional gas sorption method, is particularly appropriate for studying pore sizes in the mesoporous range.     

Motional narrowing of H NMR in annealed a-Si:H prepared by glow discharge

NMR measurements were made at 77 K and 4.2 K for hydrogenated amorphous Si films prepared by glow discharge decomposition on room temperature substrate and annealed up to 500°C. It is found that the narrow component line in the NMR signal observed at 77 K or above for films annealed above 400 °C is motionally narrowed one.     

Orientational ordering in solid orto-H2 and para-D2

Orientational ordering in rigid fcc orto-H₂ and para-D₂ is described in terms of the bifurcation of the solution of a system of nonlinear integral equations.     

H and C NMR studies of molecular orientation and dynamics in liquid crystal 6BA

The dynamics and orientation of dimers accompanying the formation and destruction of hydrogen bonds in the nematic phases of 4-n-hexylbenzoic acid (6BA) were studied by ¹³C and ²H NMR. The orientational order parameter S in the nematic phase was estimated from the quadrupole splitting of the ²H NMR spectrum. The intermolecular interaction energy for the molecular order in the nematic phase decreased with increasing temperature. The flexibility of dimers due to the destruction of the hydrogen bond is closely related to a decrease in the intermolecular interaction energy. The proportion of ²H NMR spin-lattice relaxation time (T₁) to S, which reveals the coupling of the orientational fluctuations with the hydrogen bonding processes, was observed.     

2H T2rho relaxation dynamics and double-quantum filtered NMR studies

In this study 2H T2rho DQF NMR spectra of water in MCM-41 were measured. The T2rho double-quantum filtered (DQF) NMR signal is generated by applying a radio frequency (RF) field for various durations and then observed after a monitor RF pulse. It was found that the transfer between different quantum coherences by the couplings during long-duration RF fields (i.e., soft pulses) and that residual quadrupolar interaction dominates the signal decay. Knowledge of coherence transfer during long-RF pulses has special significance for the development of sophisticated multi-quantum NMR experiments especially multi-quantum MRI applications.     

Orientational ordering and the effect of dimerization in wall-adjacent liquid layers

Comparative investigations of electronic-vibrational absorption spectra of thin layers of nonmesogenic liquids formed on dielectric and conductive substrates were carried out. Results are interpreted within the framework of Mayer–Saupe theory that takes into account the dispersion and the dipole–dipole interaction between molecules and molecular associates, and the influence of the field of surface forces as well.     

Orientational ordering in polymer composites with nanofillers: the osmotic pressure effect

Phase behavior of short double-stranded DNA molecules dissolved in the water-containing polymer matrix is considered theoretically. Flexible-chain polymer molecules are assumed to be neutral. The phase behavior of DNA fragments is shown to be governed by the effective attraction, occurring due to polyvalent cations dissolved in water, and the osmotic pressure of the flexible-chain polymer.     

Photo-induced degradation of a-Si: H diodes with an nin structure

Diodes with an nin structure consisting of hydrogenated amorphous silicon (a-Si:H) exhibit space-charge-limited currents. We subjected some diodes to both illumination and voltage stresses. Only the illumination treatment led to a degradation of the I(U)-characteristics. The degradation is reversible by annealing. We deduce from these findings that metastable traps are created by recombining photocarriers rather than by single-carrier trapping. The reversible diode degradation is consistent with the Staebler-Wronski effect.     

1H NMR studies on molecular motions of 4-aminopyridinium and pyrrolidinium cations in new ferroics

The aim of the study was to check the effect of the cation on the molecular dynamics of the anion, which is not directly observed, in different phases of the following compounds: (C4H8NH2)SbCl6(C4H8NH2)Cl, (C4H8NH2)SbCl6 and (4-apyH)ClO4, (4-apyH)SbCl4.     

1H and 13C NMR studies of molecular dynamics in the biocopolymer of glycolide and epsilon-caprolactone

Copolymers of glycolide and epsilon-caprolactone were studied using differential scanning calorimetry and solid-state NMR. The variation of the T1 relaxation time with temperature reflects local disorder and can be quantified in terms of the distribution of correlation times predicted by the Davidson-Cole model. T, relaxation is dominated by trans-gauche isomerisation, with an activation energy of 34-35 kJ mol(-1).