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Optical surface plasmon resonance (SPR) excitation can be theoretically depicted and discussed using Fresnel’s equations. However, Fresnel’s equations cannot explicitly give expressions to reflect the characteristics of SPR systems, especially in SPR optical waveguide and fibre-optic sensors. In this paper a mathematical model based on the approximation proposed by Kretschmann in bulk optics is presented to describe the characteristics of SPR optical waveguide and fibre-optic sensors. The results show that the model keeps high accuracy when used in the area close to the minimum reflection, at which the resonance condition is achieved. This model can be used to analytically estimate the performance of SPR optical waveguide sensors, and SPR fibre-optic sensors in meridional rays approximation. [ABSTRACT FROM AUTHOR]

The use of validated computational models to predict liquid spreading in fibrous materials is an important tool for understanding and optimising the function of absorbent products. The aim of this paper is to review these modelling strategies and their limitations. Experimental methods to find the closure relationships required as an input into Richards' equation (which describes the fluid transport in porous materials) are discussed. The computational models are validated against the detailed laboratory experiments of the flow of fluid from sources on inclined or horizontal homogeneous fibrous sheets, and are extended to inhomogeneous layered structures. Recent progress towards modelling simple incontinence products is described. [ABSTRACT FROM AUTHOR]

The use of nuclear magnetic resonance to make quantitative measurements of the absorption processes occurring in the constituent materials of disposable incontinence pads was investigated. Modern incontinence pads often have a layered structure with the absorbent layer principally consisting of superabsorbent polymer (SAP) grains distributed in fluffed wood pulp. T 2-weighted and magnetisation transfer contrast (MTC) measurements were made using samples of SAP, fluffed wood pulp, and a mixture of 50% SAP and 50% fluffed wood pulp following the addition of water and NaCl solutions. The T 2-weighted signal always decreased on mixing the liquid and material samples, with SAP showing the smallest magnitude of signal decline. The MTC change was minimal for SAP, but increased for the other samples. The small changes in the T 2-weighted signals and the MTC observed when adding water to SAP indicate that water is not principally being tightly bound by the polymer. The absorption time-course was further evaluated by acquiring proton-density-weighted 1D profiles after the addition of water to the samples. In SAP, the fitted time constant was comparable to the activation energy measured by other methods. The relaxation times both declined on mixing the liquids with samples of SAP and fluffed wood pulp. The reduction in spin?spin relaxation is sufficient to account for the T 2-weighted signal changes. [ABSTRACT FROM AUTHOR]

In homogeneous fibrous materials are used in many absorbent applications. Such materials often consist of multiple layers, where each layer may play a different role in absorbing liquid (for example, rapid acquisition compared with long-term storage). Simple functional-closure relationships for describing flow in multi-layered materials are developed on the basis of solutions to steady-state vertical upwards and downwards infiltration. These relationships enable multiple-layered structures to he accurately modelled as homogeneous materials. Full numerical calculations confirm that these bulk-closure relations predict steady flows in multilayered materials. The bulk models of infiltration are tested for unsteady horizontal infiltration against full numerical calculations and shown to predict the length of the wetted region and the moisture distribution, except near the front of the capillary fringe. Some consequences for the design of absorbent products are discussed. [ABSTRACT FROM AUTHOR]

Water diffusion and the concentration profile within the skin significantly affect the surrounding chemical absorption and molecular synthesis. Occluding the skin causes water to accumulate in the top layer of the skin (the stratum corneum [SC]) and also affects the water diffusivity. Scar treatments such as silicone gel and silicone sheets make use of occlusion to increase skin hydration. However with existing techniques, it is not possible to quantitatively measure the diffusivity of the water during occlusion: current methods determine water diffusivity by measuring the water evaporated through the skin and thus require the skin to breathe. In this work, we use the high sensitivity of terahertz light to water to study how the water content in the SC changes upon occlusion. From our measurements, we can solve the diffusion equations in the SC to deduce the water concentration profile in occluded skin and subsequently to determine the diffusivity. To our knowledge, this is the first work showing how the diffusivity of human skin can be measured during occlusion and we envisage this paper as being used as a guide for non‐invasively determining the diffusivity of occluded human skin in vivo. By exploiting in vivo terahertz reflection spectroscopy and skin models, this work develops a method to determine water diffusivity in occluded human skin for the first time. Dynamic water concentration and stratum corneum thickness changes upon occlusion are also tracked quantitatively. This work helps study the barrier function of the stratum corneum and will provide a new quantitative measure for use in skin studies. [ABSTRACT FROM AUTHOR]