U. Keiderling

On the structure of an asymmetric carbon membrane with a novolac resin precursor

An asymmetric tubular carbon membrane, appropriate for gas separation applications, was made through carbonization at 800°C of a precursor structure containing two phenol-formaldehyde resins, a partially cured novolac resin in 30–60 μm grains (bulk material), and a resole resin (membrane skin material). A replica of the skin material was deposited separately on a stainless steel substrate. The samples were analyzed by nitrogen adsorption, small-angle neutron scattering, and scanning electron microscopy (SEM). The basic structural entities of both skin and the bulk part were low-aspect-ratio carbon domains with a characteristic dimension in the 4.0–4.5 nm range. Further, the materials were characterized by microporosity in the 0.30–0.50 range with isotropic pores having a 1.3 nm diameter. The results are discussed with the help of a systematic survey of possible carbon structures with an intermediate level of microporosity.

Neutron scattering from water adsorbed on an alumina membrane

Abstract The pore structure of an alumina membrane was studied by adsorption in conjunction with small-angle neutron scattering (SANS). The effect of an incomplete contrast matching was investigated and simple formulae allowing the calculation of the amount of water adsorbed and the film areas, at various relative pressures, were derived for the ternary system. In the vicinity of the contrast matching point, however, incomplete contrast matching does not introduce a substantial complication to data analysis. The adsorption isotherm was reconstructed from the SANS data and agrees well with the experimental adsorption isotherm. For the alumina membrane, a coordination number of ≈10 was estimated from the SANS determined areas.

Nanostructures of the montmorillonite-derived restructured clays K10®, HMO and the Mg2+ exchanged analogue Mg-HMO. A SANS, N2 sorption and XRPD study

Small angle neutron scattering (SANS) of the montmorillonite (MO)-derived acid-restructured clays K10®, HMO and the Mg2+ exchanged congener of the latter, Mg-HMO, has been investigated. K10® is a strong acid-treated clay, HMO a new, mild-acid treated material with different X-ray powder diffraction (XRPD) characteristics and Mg-HMO a Mg2+ exchanged derivative; the scattering curve of the latter exhibits a peak at Q = 5.46 nm−1 ascribed to intra-layer Mg2+–Mg2+ distances. Analysis of the mid-Q region (0.2–2.6 nm−1) of the curves demonstrates that K10® and HMO differ in nanostructure. In particular, the solid matrix of K10® exhibits a mass fractal dimension, Dm = 2.53 which is absent from HMO but which is characteristic for sepiolites prepared via prolonged acid treatment. For Mg-HMO, recently found to be an efficient base catalyst for fine chemicals production, both XRPD and SANS point to a more ordered “parallel-plate in primary particle” shape. This is ascribed to both intercalation of Mg2+ between aluminosilicate sheets and enhanced correlation between platelets due to surface Mg2+ cations acting to bind clay platelet packets together face to face in agreement with the high Mg2+ loading level of HMO (10% w/w). The presence of the Mg2+ cations reduces the surface roughness and results in an increase of the length of the platelet packets in line with this enhanced ordering.

On the morphology and surface geometry of Vycor

Abstract A Vycor porous glass is examined by adsorption of H2O/D2O as well as CH2Br2 in conjunction with small-angle scattering of neutrons and X-rays, respectively. For dry samples, the data indicates a fractal surface with a fractal dimension D ∼ 2.6. After the deposition of an adsorbed film, defractalization is observed. However, this procedure is different for H2O and CH2Br2. It is suggested that H2O yields a soft hydrogel on the Vycor surface. Theoretical considerations on the morphology of the pore structure as well as the surface geometry are given in terms of two-dimensional fractal configurations.

Characterisation of pillared clays by contrast-matching small-angle neutron scattering

The contrast-matching SANS technique has been utilised to determine inter-pillar distances (and surface texture) in montmorillonite and beidellite pillared smectite clays; they lie in the range 1.40-1.80 nm, reflecting different inter-pillar orderings.

Investigation of lipid organization on stratum corneum by water absorption in conjunction with neutron scattering

Abstract The lipid arrangement of stratum corneum (SC) was investigated by water absorption in conjunction with small-angle neutron scattering (SANS). The SANS spectra are in reasonable agreement with previous SAXS measurements. In the lower Q region, however, there is an indication of the presence of a lipid phase with a periodicity of 32.2 nm. The position of the shoulder does not change upon hydration indicating that no swelling occurs.

Characterization of an alumina membrane by neutron scattering and other techniques

Abstract An alumina membrane was studied by three methods: adsorption, adsorption in conjunction with small-angle neutron scattering (SANS), and relative permeability (PR). The predictions of the Brunauer-Emmett-Teller and the Kelvin equations were found to be in accordance with the SANS results. Film areas and pore size distributions were calculated. For the alumina membrane, a coordination number of ∼ 10 was estimated from the SANS areas. Analysis on PR data was performed and a connectivity number of ∼ 8 was computed.