Modifying hydrophilic properties of polyurethane acryl paint substrates by atomic layer deposition and self-assembled monolayers

A process of atomic layer deposition (ALD) combined with self-assembled monolayers (SAMs) was used to investigate the possible modification of the wetting properties of polyurethane (PUR) paint surfaces without altering their original hue. First, we used an ALD process to produce thin and uniform Al₂O₃coatings of these surfaces at temperatures as low as 80 °C. We then successfully achieved the addition of 16-phosphono-hexadecanoic acid (16-PHA) SAMs to the Al₂O₃-coated paint samples. Given initial hydrophobicity, which however was not stable over time, Al₂O₃coatings reduced the contact angle of the PUR surfaces from 110 to 10°. Addition of SAMs on the Al₂O₃coatings induced a sustained reduction in their contact angles to 60-70°, and aging of the samples revealed a further decrease to 25-40°. Testing of the Al₂O₃/16-PHA coating in a Weather-Ometer (WOM) revealed its durability even under harsh outdoor conditions. These experimental results show that by combining ALD with SAMs it is possible to produce durable coatings with modified hydrophilic/hydrophobic properties that are stable over time. The use of SAMs with different end-groups may allow fine-tuning of the coating's wetting properties.