Effect of fabric texture and coating nature on water repellency

Water-repellent properties allow clothing and outdoor equipments to protect us from being wet and the textile industry still focuses on the design of clothes showing such properties. Well-established types of coatings using long chain perfluorinated compounds (C6 an C8) were used so far by the textile industry. However, because of the environmental issues these coatings cause and the risks they present for human health, several regulatory actions were taken to forbid the usage of PFAOS. Therefore, alternative solutions must be found to replace the coatings using these chemicals. This study compares the performances of three types of alternative chemicals that can be used to provide water-repellent properties to fabrics. In addition, we studied the effect of surface texture on the resulting hydrophobic properties of the coated fabrics. To do so, the three different coatings were prepared from commercial formulations. The prepared coatings were deposited on seven different fabrics with different surface roughness. We used the roughness factor $r$ defined by Wenzel among all the parameters available to describe the surface roughness. To determine the roughness factor of the uncoated and coated fabrics, we used stylus profilometry and Atomic Force Microscopy (AFM). Stylus profilometry measurements showed that the fabrics have a macroscale roughness ranging from $r=1.16$ to $r=1.86$. On the other hand, the scans performed by AFM showed that the fibers do not contribute to the surface roughness of the fabrics since the fibers appeared to have roughness factor equal to one. The assessment of the water-repellent properties of the coated fabrics was performed by measuring the contact angle, the static roll-off angle and the dynamic roll-off angle for each sample. These measurements revealed that rougher samples are more hydrophobic, i.e., an increasing roughness results in increasing water-repellent properties. Moreover, the high contact angle measured for rougher samples ($\sim$\ang{140}) showed that only the choice of an appropriate weave pattern with a defined roughness is enough to provide desired hydrophobic properties to fabrics (after being coated). Finally, these measurements revealed that the coating nature reduces or increases the static and dynamic roll-off of the fabrics. Indeed, one coating showed lower static and dynamic roll-off angles for all the studied fabrics compared to two other coatings.