Non-fluorinated superhydrophobic Al7075 aerospace alloy by ps laser processing

Abstract

The metallic surfaces with low affinity or high repellence towards water molecules are extremely desirable. The present investigation reports the development of non-fluorinated super or ultrahydrophobic aerospace aluminum alloy (Al7075) surface by laser patterning and high vacuum process for 4 h. Lamellar and lotus leaf papillae like structures covered with nanoscale protrusions are found to be formed depends on the laser fluence and spatial shifts of laser scans. The fresh laser processed hydrophilic surface was vacuum processed to create layer of hydrocarbon to reduce the surface free energy for the wetting property transformation. The analysis of the results shows the synergistic effect of hierarchical structures and dominant presence of non-polar elements is critical for superhydrophobic property. The surface geometry is primarily responsible for the wetting property transformation by entrapping μ-volume of air to generate a composite interface of solid-gas-liquid. Micro and nanoscale (dual scale) surface structures are essential for the durable and consistent superhydrophobic property with high degree of water repellence for bigger volume of water droplets. Further, sole presence of nanoscale structures on inherent hydrophilic aluminum alloy surface with predominant presence of non-polar elements can yield only near superhydrophobic surface due to random spacing of nanoscale protrusions.