Effects of Wicking Characteristics on the Accuracy of Wearable Nylon Sensors

SweatID wearable sensors consist of electrically spun nylon fabric that is treated and then functionalized to become sodium selective. The functionalized nylon is then assembled into a wearable fabric sensor (WFS), used with a corresponding electronic device, to monitor sweat sodium concentration during exercise. The monitoring is based on a resistance reading measured from the device through the WFS. It is crucial that these nylon sensors are accurate and precise, so quality control measures are needed at multiple stages. One of these measures consists of monitoring the wicking characteristics of the nylon mat at each stage. This ensures that each stage proceeds uniformly and helps to determine the orientation of the functionalized nylon during the assembly process. A modified drop test was used to determine the horizontal wicking speed and water absorbance capacity (WAC) of the nylon through its three stages in the treatment process: nylon, post-treatment pre-functionalization, and post-treatment post-functionalization. These characteristics help determine if adjustments need to be made within the process or if the nylon mats fail the quality check and a new nylon mat just be used. As the nylon mat is being processed during the treatment stage, one of the materials used during this stage is carbon nanotubes (CNT). An effect of this material is that the nylon mat has a distinctive color variation on either side of the mat due to the dispersion of the CNTs. From the wicking data gathered, further alterations can be done on fully assembled WFS, determining which side of the nylon mat is more sensitive to the resistance reading due to the color variation. The third stage in the process is the functionalization stage, where calixarene is used to functionalize the treated nylon post-CNT. The calixarene coats the mat, causing a significant change to the wicking properties of the nylon. A quality control measure can be implemented through the change in properties to ensure a consistent distribution of calixarene over the treated nylon mat. This change is validated through standard in-lab calibration testing and repeat in-person testing on indoor cycles. The future of these WFSs hopes to continue into the eventual integration into fabric athletic apparel, so as more data is acquired about these wicking characteristics, the better the integration of better fabrics can be achieved and the closer these sensors can reach these expectations.