2014 cover competition runners up Dario Donnarumma and colleagues discuss their winning image.

Explore more winning images, that will be featured on the 2016 covers of the Materials Today journal.

Cotton is the most common textile material, frequently used in clothes making but also in medical and industrial applications; it is light, soft, and has a high water absorption capacity. Its special properties make cotton widely used also in combination with other textile materials to form artificial fibers [1, 2]. Cotton fabrics can be defined as fibrous porous materials. All fabrics are in fact porous media having a hierarchical structure with different characteristic scales, starting from the nanopores present in each cotton fiber. Larger pores, in the range of microns, are found between the fibers, which are twisted together to form a yarn. Finally, even larger porosity, on the scale of 100 microns, can be seen between individual woven yarns. This porosity can be changed depending on the way the fabrics are knitted and strongly influences textile characteristics such as mass, thickness, draping ability or air permeability [3, 4]. Despite its common use, and involvement in relevant application, the role played by cotton fabrics microstructure in its properties is still not fully elucidated. An advanced investigation of this system, based on modern experimental technologies, such as advanced microscopy, would result in a valuable advancement in many fields. There are few systematic investigations of quantitative relations between constitutive parameters, fabrics topography and tissue wettability. The basic understanding of knitted cotton structure and its correlation with liquid adsorption properties represent an important issue in tissue functionalization, a field that arose in the last decade [1, 5].

Focus on apparel complexity: Cotton fabric topography by CLSM

As reported in our recent work[6], the adsorption/desorption properties of cotton fabrics can be investigated by dynamic vapour sorption (DVS) technique to correlate the water transport properties inside fabrics to its porous structure. This investigation can be associated with a characterization of cotton porosity at different length-scale by confocal laser scanning microscopy (CLSM), which allows to image structures in the focal plane while suppressing out-of-focus components. The scanning of the focal plane through the object being imaged enables the collection of three-dimensional microscopic image data sets, also known as z-stacks. The image on this issue's cover of Materials Today shows a 100% cotton fabrics with a plain wave knitting imaged through a confocal microscope (Zeiss LSM 5 PASCAL). The fabric was preliminarily soaked in an aqueous solution of a fluorescent marker (Rhodamine B, concentration 1 µg/ml) in order to highlight the textile structure. A z-stack consisting in 65 optical slices at a distance of 5 μm from each other along the z axis (total height=325 μm) was acquired with a low magnification optics (10x objective). A HeNe laser at 543 nm was used to excite the sample and the emitted light was recorded at 600 nm by a photomultiplier tube. After image acquisition, a 3D processing of the z-stack was performed by an extended depth of focus algorithm implemented by a commercial image analysis software (Image Pro Plus 7). The algorithm selects in each image of the z-stack the pixels in focus and then merges them together in a single resulting image. An example of the latter is shown in the cover image (size: 744 μm x 744 μm).

3D reconstructions such as the one in the cover image can be used to evaluate geometrical properties of the fabrics, such as the porosity at the micron scale. In turn, this information can provide some insight on the distribution of water inside the fabrics, which is relevant for investigating both water penetration, such as in tissue functionalization, and evaporation, such as in fabrics drying. Concerning the latter, evaporation from porous media is a topic of growing interest in view of its industrial relevance and of the multiple spatial scales present in the problem. Common, not fully elucidated features of evaporation from porous media are a constant drying rate phase followed by a falling drying rate phase. In our work [6], we use cotton fabric as a model porous medium and study the effects of additives such as salts and surfactants on the evaporation of water. One of the main results is that these additives affect the constant, but not the falling rate phase of the drying process. Furthermore, taking distilled water as the reference, the constant drying rate of wet fabrics was found to increase for the surfactant solution and for aqueous salt solutions up to some hardness value, in contrast to the bulk behavior. All these results point to the role played by topography and wettability of cotton materials in determining water distribution and evaporation.

D. Donnarumma1, *, S. Caserta1, 2 and S. Guido1, 2
1 Laboratory of Chemical Engineering @ the Interface, Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università degli Studi di Napoli Federico II, P.le V. Tecchio 80, 80125 Napoli, Italy.
2 Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), UdR INSTM Napoli Federico II, P.le Tecchio, 80, 80125 Naples, Italy.

* Corresponding author: Donnarumma, D. (dario.donnarumma.ita@gmail.com)

Further reading

  1. Hinestroza, J.P., Can nanotechnology be fashionable? Materials Today, 2007. 10(9): p. 64.
  2. Smith, J. and S. Bhatia, Natural fibers raise social issues. Materials Today, 2005. 8(11): p. 72.
  3. Kumpikaite, E. and A. Olšauskiene, Influence of fabric structure on some technological and end-use properties. Fibres & Textiles in Eastern Europe, 2003. 11(2): p. 41.
  4. Englund, K., Tribology of natural fiber polymer composites. Materials Today, 2009. 12(3): p. 45.
  5. Alongi, J., et al., A new era for flame retardant materials? Materials Today, 2014. 17(4): p. 152-153.
  6. Donnarumma, D., et al., Water evaporation from porous media by Dynamic Vapor Sorption. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2015. 480: p. 159-164.