Determination of critical surface tension of wetting of textured water-repellent surfaces

The object of study is aluminum textured with a femtosecond laser and modified with silanes to reduce surface energy. The presence of a special texture on the surface, such as protrusions or hairs, and the inherently low surface energy of the material allow maximizing the water repellency properties. The determination of the critical wetting surface tension by the Zisman method has a pronounced wetting transition point, but the coordinates of this point cannot be accurately predicted. In this work, the Zisman method is considered as a tool for comparing the effectiveness of modifiers for femtosecond laser-textured surfaces. In this work, periodic structures were created by laser ablation on the surface of aluminum, the surface was modified to achieve the Cassie state when wetted with water, and the critical surface tension of wetting was determined by the Zisman method. As a result, it is shown that the Zisman method in combination with the data on the water contact angle values is an effective tool for characterizing the quality of surface modification of textured samples. It is shown that for textured aluminum surfaces, the most effective modifier is silane, which maintains the Cassie wetting state, with a contact angle increased from 155 to 160°. Paraffin has been shown to be a less effective modifier with an implicit wetting plateau and a transition in the range of 30 to 40 mN/m. It is shown that the textures that have acquired water repellency in the course of spontaneous hydrophobization are very unstable to the action of liquids with reduced polarity, although they have high values of the water contact angle. In practice, the creation of water-repellent coatings on aluminum is a promising substrate due to their widespread use in the aviation, automotive, and energy industries due to their high mechanical strength, lightness, and stability of properties.