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Title: Dynamic spatially resolved unilateral NMR measurements of liquid ingress and vapour adsorption and desorption in heterogeneous layered fabrics
Author: Adriaensen, H.
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2010
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This thesis presents investigations of liquid ingress and vapour uptake in different porous media including textile fabrics and activated carbons, monitored by means of a unilateral NMR instrument. The aim of this work is to assess protective materials which prevent toxic liquid ingress and toxic vapour uptake from contaminating materials and personnel. A high performance fabric made of a combination of coated and not coated fibres can provide extremely high protection against toxic liquids. By incorporating an adsorbent layer between two highly repellent layers, an “intelligent” fabric that can prevent complete penetration through the composite system by toxic vapours can be constructed. This project was undertaken with a low-field unilateral profile NMR Mouse® (MObile Universal Surface Explorer) which can collect signal from a thin and flat sensitive volume (ca. 1.5 cm x 1.5 cm x 0.6 mm) up to 10 mm above it, and in a non-invasive manner. The instrument uses a strong inherent magnetic field gradient (11.38 T.m-1) in conjunction with pulsed radio frequency waves. The method makes use of Fourier Transformed NMR in order to spatially resolve 1D vertical profiles for each measurement over a field of view exceeding 500 µm and with a spatial resolution of 15 µm. One system investigated was a laminate heterogeneous layered fabric, made of a horizontal stack of three individual layers, each 70 μm thick, constructed from entangled fibres of 10 µm in diameter. The top and bottom layers are strongly repellent to the oil used as a model that represents a simulant for a toxic liquid, whilst the middle layer is non-repellent and allows oil to absorb inside. The ability of the liquid challenge (source of hydrogen-containing molecules in the form of a droplet) to penetrate the textile structure depends on the external pressure applied to the droplet; the effect of this pressure is extensively investigated in this work. In further experiments, the middle layer of the fabric was replaced by an activated carbon cloth textile layer (200 μm thick) made of woven fibres. Activated carbon is an extremely powerful adsorbent into which one or more challenge(s) can be adsorbed at a time and has therefore a great aptitude to contribute to the effectiveness of protective textiles. In this work it is demonstrated that the ingress of liquids as a function of pressure vertically applied to the top of the sample can be dynamically monitored via a vertical stack of 1D NMR profiles. It was possible to non-invasively and non-destructively quantify the amount of liquid penetrating into the middle non-repellent layer (or activated carbon cloth layer) as a function of pressure. The ability of unilateral NMR to monitor the adsorption process of vapours onto activated carbons cloths was also explored. The monitoring technique was extended to other types of activated carbons including monoliths and composites. Spatially resolved one dimensional profiles of both the transverse NMR relaxation rate (R2) and the absolute quantity of adsorbate present at a given position across the selected slice were obtained for three different activated carbons (monolith, composite and cloth) which are challenging samples from the point of view of their electrical conductivity. The NMR amplitude is shown to strongly correlate with T2 and, when calibrated, the NMR amplitude is shown to reveal the saturation level. The NMR relaxation rate reveals subtle information about pore filling, which allows quantitative assessment of the system’s saturation level, without the need for calibration, provided that the molecule under investigation is known. Differing dynamic variations in R2 are seen for one adsorbate to another. For the case of ingress into textile cloth layer, the data suggests that the bigger pores are filled before the smaller pores.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available