Moulding hydrodynamic 2D-crystals upon parametric Faraday waves in shear-functionalized water surfaces

Faraday waves, or surface waves oscillating at half of the natural frequency when a liquid is vertically vibrated, are archetypes of ordering transitions on liquid surfaces. Although unbounded Faraday waves patterns sustained upon bulk frictional stresses have been reported in highly viscous fluids, the role of surface rigidity has not been investigated so far. Here, we demonstrate that dynamically frozen Faraday waves-that we call 2D-hydrodynamic crystals-do appear as ordered patterns of nonlinear gravity-capillary modes in water surfaces functionalized with soluble (bio)surfactants endowing in-plane shear stiffness. The phase coherence in conjunction with the increased surface rigidity bears the Faraday waves ordering transition, upon which the hydrodynamic crystals were reversibly molded under parametric control of their degree of order, unit cell size and symmetry. The hydrodynamic crystals here discovered could be exploited in touchless strategies of soft matter and biological scaffolding ameliorated under external control of Faraday waves coherence. There is a renewed interest in Faraday waves patterns in the field of nonlinear metamaterials due to their tunable templating capacity. Kharbedia et al. show that free-standing water surfaces with ordered patterns can be generated and controlled by the Faraday waves with help of stiffening surfactants.

Automated summary

The study demonstrates that dynamically frozen Faraday waves, called 2D hydrodynamic crystals, appear as ordered patterns of nonlinear gravity-capillary modes on water surfaces functionalized with soluble surfactants. The phase coherence and increased surface rigidity lead to the Faraday waves ordering transition, allowing for reversible control of the hydrodynamic crystals' degree of order, unit cell size, and symmetry. These newly discovered hydrodynamic crystals could be utilized in touchless strategies for soft matter and biological scaffolding, enhanced under external control of Faraday waves coherence.