In order to simplify the complex application process of traditional multi-layer coatings, the work aims to optimize solvent combinations and resin ratios, enabling the coating to spontaneously stratify after a single application. This drives silicone resin migration to the surface layer while polyurea resin migrates to the underlying layer, which allows coatings to possess hydrophobic properties and anti-algae adhesion, and maintain mechanical strength, meeting the requirements for environmental sustainability and high-performance efficiency in shipbuilding and related industrial applications. The KH330-modified silicone resin and polyurea resin were dissolved in a mixed solvent via a one-pot method. Curing agents and catalysts were then added, followed by uniform stirring and brushing onto the substrate. The coating was cured at room temperature to form a stratified layer. The delamination behavior of the coating was characterized by resin solubility parameter analysis, dynamic mechanical analysis (DMA), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). The performance and mechanical properties of the coating were evaluated via contact angle measurements and surface energy calculations, seawater immersion testing, inhibition of diatom adhesion, and adhesion tests. Through analysis with the Hansen Solubility Parameters (HSP) method and interfacial energy theory, it was confirmed that the silicone and polyurea resins exhibited significant differences in solubility, compatibility, and surface energy, satisfying the conditions for stratification. Optimal coating delamination was achieved in a mixed solvent system of butyl acetate and xylene at a 1∶1 mass ratio. This solvent system demonstrated a moderate evaporation rate, ensuring that phase separation was completed prior to gelation. The self-stratifying coating consistently showed contact angles exceeding 100° with surface free energy between 20-30 mJ/m2. After immersion in artificial seawater, the contact angles and surface roughness of the coating remained stable with no observed swelling or delamination. In the anti-algae adhesion experiments, the Silicone-PUa-x coatings demonstrated progressively higher inhibition rates against algae as the silicone content increased. Specifically, Silicone-PUa-10 exhibited an anti-adhesion rate of 24.6% against Chlorella after immersion for 24 h, while Silicone-PUa-40 achieved a significantly higher rate of 61.6%. Similarly, the test with Navicula showed that the anti-adhesion rates for Silicone-PUa-10 and Silicone-PUa-40 were 9.8% and 66.2% after 24 h immersion, respectively. Adhesion tests indicated that the incorporation of polyurea resin significantly enhanced the coating's bonding strength (>3.0 MPa). In the silicone/polyurea self-stratifying coating system, the solvent evaporation rate plays a critical role in regulating the microphase separation process. Therefore, the solvent evaporation rate should be optimized, because high surface energy resins require highly polar/volatile solvents, while low surface energy resins demand the opposite. However, the solvent evaporation rate should not be excessively high. If evaporation occurs too rapidly, it may lead to premature cross-linking of the system before complete formation of the heterogeneous structure and phase separation, resulting in insufficient stratification or even non-layered phenomena. Therefore, the mixed solvent system of butyl acetate and xylene (1∶1 ratio) with its moderate evaporation rate achieves the optimal stratification. As for performance, it is found that increasing the silicone content reduces the coating's surface free energy and enhances hydrophobicity, thereby improving anti-algae adhesion properties. Simultaneously, the incorporation of polyurea resin significantly strengthens the adhesion between the coating and the substrate, ensuring long-term stability.
Key words
self-stratifying coating /
silicone resin /
polyurea resin /
solvent /
anti-algae adhesion performance
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Funding
Major scientific and technological projects in Xiamen (3502Z20231049)
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