Investigations of homologous disaccharides by elastic incoherent neutron scattering and wavelet multiresolution analysis

Self-assembly Processes in Hydrated Montmorillonite by FTIR Investigations

Experimental findings obtained by FTIR and Raman spectroscopies on montmorillonite-water mixtures at three concentration values are presented. To get some insight into the hydrogen bond network of water within the montmorillonite network, FTIR and Raman spectra have been collected as a function of time and then analyzed following two complementary approaches: An analysis of the intramolecular OH stretching mode in the spectral range of 2700–3900 cm⁻¹ in terms of two Gaussian components, and an analysis of the same OH stretching mode by wavelet cross-correlation. The FTIR and Raman investigations have been carried as a function of time for a montmorillonite-water weight composition (wt%) of 20–80%, 25–75%, and 35–65%, until the dehydrated state where the samples appear as a homogeneous rigid layer of clay. In particular, for both the FTIR and Raman spectra, the decomposition of the OH stretching band into a “closed” and an “open” contribution and the spectral wavelet analysis allow us to extract quantitative information on the time behavior of the system water content. It emerges that, the total water contribution inside the montmorillonite structure decreases as a function of time. However, the relative weight of the ordered water contribution diminishes more rapidly while the relative weight of the disordered water contribution increases, indicating that a residual water content, characterized by a highly structural disorder, rests entrapped in the montmorillonite layer structure for a longer time. From the present study, it can be inferred that the montmorillonite dehydration process promotes the layer self-assembly.

Resolution-elastic neutron scattering by correlation techniques

Neutron scattering applications often require discriminating the elastic contribution from the inelastic contribution. For this purpose, correlation spectroscopy offers an effective tool with both pulsed and continuous neutron sources as well as several advantages: the analysis of the neutron velocity distribution can be carried out with a duty factor of 50%, independently on the resolution value; the best statistical accuracy for spectra where the elastic part encompasses most of the integrated intensity is provided. Depending on the statistical chopper position, correlation analysis can be used for both incoming and outgoing neutron velocity determination. Moreover, the correlation technique is very profitable for investigating weak signals in the presence of high background, which is often the case for small samples. To provide instrument flexibility and versatility, an innovative approach comprising tuning resolution by variable Resolution-Elastic Neutron Scattering (RENS) is proposed, offering further benefits by enabling systematic trading of intensity for resolution and vice versa. This study puts into evidence the advantages offered by the use of statistical chopper and of correlation technique for RENS in choosing the best compromise between resolution and beam intensity.

Ethylene Glycol - Polyethylene Glycol (EG-PEG) Mixtures: Infrared Spectra Wavelet Cross-Correlation Analysis

Infrared spectra were collected on mixtures of ethylene glycol (EG) and polyethylene glycol 600 (PEG600) as a function of weight fraction from pure EG to pure PEG600. In this paper, it will be shown that while the OH vibrational contribution drastically reduces its center frequency from 3450 cm^-1 to 3300 cm^-1 in the weight fraction range 0-25%, the displacement of the mixture spectral features of the mixtures from ideal behavior, i.e., in the absence of interaction, shows the presence of a non-ideal mixing process. Furthermore, wavelet cross-correlation analysis of the registered pairs of spectra and of the intramolecular O-H stretching contributions reveals how the addition of a small amount of pure EG to PEG600 dramatically influences the structural properties of the polymeric matrix, owing to an increase the intermolecular connectivity. In particular, the wavelet cross-correlation parameters, evaluated between each pair of the registered data as a function of weight fraction, in a linear-logarithmic plot, reveals an inflection point for a weight fraction of about 25% of EG, which confirms that, within the three-dimensional networks of hydrogen-bonded EG-PEG600 molecules, a key role is played by EG in determining an increase in the hydrogen-bond network density.

New generation non-stationary portable neutron generators for biophysical applications of Neutron Activation Analysis

BACKGROUND

Neutron sources are increasingly employed in a wide range of research fields. For some specific purposes an alternative to existing large-scale neutron scattering facilities, can be offered by the new generation of portable neutron devices.

SCOPE OF REVIEW

This review reports an overview for such recently available neutron generators mainly addressed to biophysics applications with specific reference to portable non-stationary neutron generators applied in Neutron Activation Analysis (NAA).

MAJOR CONCLUSIONS

The review reports a description of a typical portable neutron generator set-up addressed to biophysics applications.

GENERAL SIGNIFICANCE

New generation portable neutron devices, for some specific applications, can constitute an alternative to existing large-scale neutron scattering facilities. Deuterium-Deuterium pulsed neutron sources able to generate 2.5MeV neutrons, with a neutron yield of 1.0×10⁶n/s, a pulse rate of 250Hz to 20kHz and a duty factor varying from 5% to 100%, when combined with solid-state photon detectors, show that this kind of compact devices allow rapid and user-friendly elemental analysis. "This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo".