Ordering in a nematic side-chain polymer. A proton and deuterium nuclear magnetic resonance study

 The aim of this work is to study in detail the orientational structure of liquid-crystalline polymers with different molecular weight. The advantage of our approach is the use of broad-band ¹H and ²H NMR spectroscopy for the analysis of the orientational order of the main-chain and mesogenic groups in conjunction with small-angle neutron scattering results. Investigations of a series of partially deuterated side-chain polymers with methoxybenzylbenzoate mesogenic groups have been carried out. The deuteration of the main chain enables separate access to order and orientation effects of the side chain and the main chain. The molecular orientation of the substances investigated can be frozen in its nematic phase below the glass-transition temperature. It is independent of the molecular weight, whereas the dynamics of the director reorientation (rotational viscosity) in the nematic phase strongly depends on the molecular weight. The main-chain deuterons provide powder spectra after orientation of the polymer in magnetic fields, indicating a very weak or lacking orientational anisotropy. A complete decoupling of the main and the side group can be deduced. Received: 15 September 1999 Accepted: 7 February 2000     

Probabilistic error bounds on constraint violation for empirical-analytical Lagrangian models of motion

Nonlinear Dynamics - In contrast to many systems studied in the field of classical mechanics, models of animal motion are often distinguished in that they are both highly uncertain and evolve in a...     

Impact related changes in mineral properties: Ti-magnetite from basaltic rocks at Lonar crater, India

Samples from vesicular Lonar impactite have been investigated by Mössbauer spectroscopy and SEM in combination with elemental analysis. Observation reveal the new-formation of oxide minerals have occurred with nucleation in particular at the walls of the vesicles interpreted as having formed from condensation of the gas phase having caused the vesicles to form in the first place. Elemental analysis of Ti-magnetites gives very similar compositions irrespective of the oxides grains being vesicle or matrix associated (Fe/Ti ratios approximately 3). The room temperature spectra of the oxides show magnetically ordered components due to A, B, and C sites in the substituted spinel. The occurrence of these ordered components are not in accordance with expectations from the bulk chemical compositions, suggesting the presence of fine scaled intergrowth of Ti-oxide and Ti-magnetite.     

Maghemite in basalt studied by Mössbauer spectroscopy in external magnetic field

In the present study, we investigate the feasibility of detecting and determining the presence of maghemite in rock samples, by obtaining Mössbauer spectra in an external magnetic field of 1.6 T at room temperature. The interaction of the external magnetic field and the magnetic moments of the sublattices will induce differential shifts in the peak positions. By this method, we can assign some lower limit of the amount of maghemite in the sample. The results are compared with a model for a mixture of maghemite and stoichiometric magnetite.     

Nanocrystallinity induced by heating

Samples of akaganeite (β-FeOOH) and goethite (α-FeOOH) have been studied after heating at various temperatures up to 800 °C. X-ray diffraction and Mössbauer spectroscopy measurements showed that slightly below the temperatures at which the samples transform to hematite (α-Fe₂O₃) the oxyhydroxide phases become nanocrystalline.     

Formation and microstructure of cubic metastable iron silicides synthesized during pulsed laser annealing

Hyperfine Interactions - The phase formation and crystallization processes of metastable [CsCl]Fe1?x Si phases were investigated by irradiating?-FeSi/Si(111) thin films with a pulsed...