Viscoelastic droplet impact on flexible superhydrophobic mesh beams: coupled fluid-structure dynamics

Viscoelastic droplet impact on permeable surfaces is relevant to both natural systems (e.g., permeable leaves) and industrial applications such as mesh-based droplet/particle capture. Literature has demonstrated that, for water droplets, the dynamics of the beam during impact, especially cavity collapse and the detachment of liquid penetrating the mesh, significantly affect the impact force and subsequent beam motion [28]. However, this behavior markedly differs for viscoelastic droplets. The viscoelastic ligaments formed by penetration of the liquid into the mesh do not detach, altering momentum transfer, droplet evolution, and interactions with flexible substrates. We hypothesize that this non-detaching ligament dynamics and beam flexibility lead to a different coupled droplet-beam response, which remains unexplored.

We performed viscoelastic droplet impact experiments on flexible, permeable mesh structures. The effects of droplet (polymer concentration, impact velocity) and mesh (opening size) parameters, as well as the impact point from the fixed end, on the coupled droplet-beam and ligament dynamics were studied. The coupled dynamics are modeled by a two and three-degree-of-freedom (DOF) spring-damper system.

The interaction between the PEO liquid and the mesh surface reduced the recoil force induced by the impact of the rims on the mesh. Moreover, the ligament dynamics, including their retraction and impact on the mesh surface, reduced the beam's energy and deflection compared to water cases. Spray formation in water droplet cases reduced the impact force at high impact velocities, resulting in greater beam deflection in PEO cases. The novel 3DOF model captured the higher modes of beam vibration well.