We investigate wicking in textiles using neutron radiography on fabrics of two types, woven and simple jersey knit, and made of yarns of four different materials: cotton, polyethylene terephthalate, polyamide and polypropylene. Moisture distribution in the samples is quantified from the images, and the total mass is compared with gravimetric measurements for validation. The position of the front versus time is obtained from segmented neutron images and backlight images, with good agreement between the two measurement methods. Using a power law to fit the height versus time curves, values for the wicking ratio are found to depart substantially from the 0.5 predicted by the Lucas-Washburn equation. The sharp front approximation is found to be a good approximation for slow wicking fabrics but is an incomplete description of the moisture on high absorbing fabrics such as cotton. The variation of yarn material is the main contributor to the difference of wicking ratio among samples. Finally, neutron moisture profiles complemented with X-ray tomography allow to differentiate two regions in cotton wetted by wicking: intra-yarn wetting and wetting covering the yarns and the inter-yarn voids.

This review covers imaging techniques of wicking in textiles ranging from visible light to synchrotron x-ray. First, the wicking phenomenon and its relevance are exposed. Then, the main wicking experimental setups, namely the strip test and the spot test, are described. Next, the imaging techniques are described together with the relevant studies applied to wicking. Finally, the analysis of wicking measurements is presented. The conclusion presents imaging techniques applied to wicking in a historical perspective and highlights areas where further development is desirable.

With synchrotron X-ray phase-contrast computed tomography, we document the wicking process at the fiber scale in cotton, polyethylene terephthalate and polypropylene yarns. A new segmentation procedure is developed, allowing a clear separation of the water and the fiber in the reconstructed images. From the water configurations, we obtain moisture content profiles over the height of the yarn and time-resolved three-dimensional visualization of the wicking process. The water filling over the height of the yarn is highly non-uniform, since the available pore space varies strongly along the yarn due to the twisting of the yarn. For the first time, a wicking in two stages is observed: an initial fast unsaturated wetting along the fiber direction followed by a main saturated flow characterized by large jumps in moisture content at discrete time steps. These jumps occur when large pore segments become filled suddenly from multiple entry points through small size throats connecting different pore segments.