F. G. Carvalho

SANS Study of Zirconia-Silica and Titania-Silica Hybrid Materials

New silica-based hybrid materials have been produced by the sol-gel process. Samples with compositions xMO2·(100 − x)SiO2 (with M = Zr, Ti and x ≤ 10 mol%) were prepared with polydimethylsiloxane, silanol terminated, with different molecular weights. In the present work the microstructure of samples prepared with a volume ratio organic/inorganic of 2/3 was investigated by Small Angle Neutron Scattering. The results show that a rather homogeneous hybrid material can be obtained. It is observed that the polymer is well distributed in the inorganic matrix and that the addition of MO2 perturbs its local conformation when it has low molecular weight. The inorganic oxide network in the hybrid was found to develop as in pure inorganic dried gels.

Investigation of Organic-Inorganic Hybrid Materials Prepared by Irradiation

New silica-based hybrid materials have been produced by gamma irradiation of the precursors using a 60Co source. An inorganic mixture of tetraethylorthosilicate with addition of Zirconium propoxide (PrZr) (x = 0, 5 and 10 mol%) was used together with polydimethylsiloxane (PDMS) silanol terminated. Samples with volume ratios organic/inorganic of 4/1, 3/2, 1/1, 2/3 and 1/4 were prepared. The irradiation dose for gel point was observed to depend on the PDMS/ INORG. volume ratio, as expected. That dose increases with decreasing volume ratio. Samples with PDMS/ INORG = 2/3 were irradiated to several irradiation doses above that corresponding to the gel point, which becomes higher for higher fraction of PrZr added. The resulting samples are homogeneous, transparent and flexible being able of swelling in a good solvent of the polymer. The microstructure of the samples was investigated by Small Angle Neutron Scattering. Samples were measured as prepared, and immersed in deuterated cyclohexane. Results indicate the presence of oxide dense clusters interconnected by polymer structures. The addition of PrZr in the preparation stage increases the density of the clusters and decreases their size.

Solving the problem of SANS instrument optimization

The problem of the optimization of small-angle neutron scattering instruments installed at steady neutron sources is discussed. The optimum solution is shown to be that in which full use is made of either the available luminous area of the source or the available hall space and not necessarily that corresponding to the equal-flight-paths design. Design criteria and their implementation are discussed taking into account space constraints on the instruments layout. It is shown that the performance of currently operating SANS facilities can be substantially improved by following the optimization procedure proposed by the authors.

Design optimization of a small angle neutron scattering spectrometer

Abstract Optimized design parameters of a small angle neutron scattering spectrometer are discussed. It is shown that the detector count rate can be optimized for constant angular resolution and a fixed neutron source area — the maximum luminous area available. This leads to a detector count rate higher than that obtained with a spectrometer optimized for fixed total flight path length and the same angular resolution. The relative gain in intensity depends upon the size of the neutron emitting surface available to the spectrometer. When optimization is hindered by space constraints the gain compared to the conventional design can still be relevant.

Optimization of a small angle neutron scattering spectrometer using a fixed collimation path

Abstract SANS spectrometer design optimization is discussed. It is shown that a fixed collimation path length properly chosen leads to higher count rates than the conventional design of equal source-sample and sample-detector flight paths. Results are applied to an actual situation using no guide tubes.

A contribution to the practical implementation of a variable-geometry converging multichannel collimator for SANS

The feasibility of constructing a variable-geometry converging multichannel collimator consisting of interlaced planes of thin neutron-absorbing strips is discussed. A process is reported for producing strips of a composite material incorporating gadolinium oxide as the neutron absorber with the required mechanical and neutron-absorbing properties.

Multichannel collimation for SANS instruments

Abstract An analytical study of converging multichannel collimation on the performance of a SANS instrument is presented. The results indicate that, for the usual resolution required in SANS measurements, this kind of collimation can provide count rate gains of one order of magnitude, relative to single-channel collimation.

Intensity and resolution effects in converging multichannel collimators for SANS by Monte Carlo simulation

A study of the contribution of the individual channels of a converging multichannel collimator to the operation of the device is carried out by means of a Monte Carlo computer simulation. The simulation shows that the coupling between the divergence of the incident neutron beam and the inclination of the individual CMC channel axis relative to the beam direction modulates the channel performance as far as intensity and resolution of the transmitted neutrons are concerned. While this does not impair in any significant way the usefulness of the device, the results are helpful to the designer.