Superhydrophobic PTFE/MWCNT coatings fabricated by supercritical fluid processing with controlled wettability

Superhydrophobic PTFE/MWCNT composite coatings were fabricated via supercritical fluid processing followed by air-spray deposition to control hierarchical surface architectures. The composites were prepared at PTFE: MWCNT mass ratios (w/w) of 10:1, 10:2, and 10:3 (corresponding to ~ 9.1-23.1 wt% MWCNT) to conduct a more systematic evaluation of the influence of nanotube loading on surface morphology and wettability. Structural and chemical analyses (Raman, FTIR, XRD) confirmed the successful incorporation of MWCNTs without compromising the integrity of the PTFE matrix. Morphological characterization (FESEM, HRTEM, and AFM) confirmed the formation of interconnected micro-nano hierarchical features governed by nanotube dispersion and concentration. All coatings demonstrated superhydrophobic characteristics, with the highest water contact angle measuring 156.3° observed at the optimal 10:2 (w/w) composition. This performance is attributed to an optimal balance between surface roughness, uniform nanotube dispersion, and effective air entrapment within the hierarchical structure. The modulation of wettability was extended to the number of spray passes, with the second coating cycle being the most effective in surface architecture. Such observed behavior is supported by a structure-wettability correlation based on a hierarchical morphology and air fraction. These results demonstrate that supercritical fluid processing enables a coherent control of the nanotube dispersion, scalable fabrication of PTFE-based superhydrophobic coatings, and a robust processing-structure-property paradigm for designing advanced water-repellent surfaces.