Preparation of Nano TiO2 Superhydrophobic Coating Based on Palmitic Acid Modification

Several methods are available for preparing superhydrophobic surfaces. However, their practical applications are limited owing to imperfections in their modification and hydrophobicity mechanisms. Therefore, investigating the mechanisms underlying the formation of superhydrophobic surfaces is crucial. Additionally, the preparation method and material selection for superhydrophobic surfaces have a significant impact on cost and environmental considerations. In this study, we chose palmitic acid (PA)-modified titanium dioxide (TiO2), which has a low surface energy and is environmentally friendly and cost-effective. Our objective was to prepare a highly efficient superhydrophobic surface using this material and analyze its modification and hydrophobicity mechanisms. Experimentally, we prepared suspensions with varying modification ratios and applied them to polished aluminum surfaces using a two-step spraying method. The chemical reactions between TiO2 nanoparticles and PA were analyzed using a Fourier infrared spectrometer. Scanning electron microscopy was used to characterize the morphologies of the superhydrophobic surfaces. A contact angle meter was used to evaluate the wetting performance of the samples by measuring their surface contact and rolling angles. To further investigate the modification mechanism and effect of different modification ratios on the surface wetting behavior, we utilized a molecular dynamics simulation method. Different models consisting of varying numbers of molecule-modified nano-TiO2 (101), were constructed. Additionally, various surface-wetting models have been developed to simulate different wettabilities. The COMPASS II force field was then employed for molecular dynamics simulations to analyze and study the modification mechanism and microscopic wetting behavior through system configuration. The root-mean-square displacement and radial distribution functions were calculated to obtain meaningful results. Overall, this research aims to elucidate of the mechanism underlying superhydrophobic surface modification and provide insights into the influence of different modification ratios on the wetting behavior at the molecular level. Validation using macroscopic experiments and microscopic molecular dynamics simulations confirmed that different modification ratios result in distinct micro-nanostructures with significant impact on surface wettability. Through characterization tests, the optimal modification ratio was identified to be 0.2 g of the PA weight and 1 g of TiO(2 )weight. At this ratio, a superhydrophobic surface was successfully prepared, exhibiting a contact angle of 164.4 degrees and a rolling angle of 2 degrees. Meticulous analysis revealed that bonding between PA and nano-TiO2 occurred via hydrogen bonding, followed by subsequent dehydration condensation reactions that culminated in the formation of ester bonds. When the head of the PA molecules is grafted onto the TiO2 surface, the tail is expelled and oscillates in a swaying motion. This unique adsorption mechanism creates a hydrophobic film composed predominantly of alkyl chains, which effectively transforms the inherent hydrophilic properties of the surface. Notably, the optimal modification ratios not only yield surfaces with low surface energy but also facilitate the development of a hierarchical micro-nanostructured surface, thereby augmenting the superhydrophobic characteristics. By combining macroscopic experiments and microscopic molecular dynamics simulations, this study analyzed the mechanism of PA-modified nano-TiO2 along with the impact of different modification ratios on surface wettability and hydrophobicity. These findings further refine our understanding of superhydrophobic surfaces, which hold immense significance for their preparation and research. Nevertheless, one limitation became apparent in this study, primarily concerning the opaque white appearance of the coating derived from PA-modified TiO2. Unfortunately, this monochromatic attribute significantly restricts extensive application. Consequently, the development of a coating with the ability to assume a diverse range of colors or achieve transparency would undoubtedly yield substantial benefits, facilitating a more versatile utilization of superhydrophobic surfaces. This aspect should be further explored in future studies to enhance the applicability of these surfaces in various practical settings.