Influence of fluid viscosity on elastocapillary coiling*

A typical spider web is composed of different types of silk, each with a specific purpose. The capture thread is a soft, extensible silk decorated with sticky glue droplets, which capture prey. Elastocapillary interactions cause the silk thread to buckle and then coil within the glue droplets as the thread is compressed. The surface tension of the droplets pulls on the fiber, keeping it taut. This means that a capture thread decorated with glue droplets can be compressed and remain taut, far beyond the length at which an uncoated fiber would begin to sag. It is hypothesized that this feature evolved to prevent the web from tangling with itself during wind loading or insect impact. We expand upon previous studies by exploring the effects of droplet viscosity on the dynamic response of the drop on the fiber system. We use a model system composed of polymer fiber and silicone oil droplets and measure the sub-micro newton tension in the thread during coiling using micropipette force sensing. The results of this study provide a deeper understanding of how spider webs work and could be used to create solid-liquid hybrid metamaterials.