3.4. CA measurements
Contact angle (CA) measurements were conducted to investigate the wettability of RP, AP and SP. Images of water and oil contact angles were shown in Fig. 3. It was found that RP exhibited low CA of 82.2° (Fig. 3(a)), while the CAs of AP and SP were up to 120.6° (Fig. 3(b)) and 128.1° (Fig. 3(c)). In addition, an oil droplet could rapidly penetrate into the SP in less than 1 s, and the oil contact angle was 0° (Fig. 3(d)–(f)), which indicated SP shows hydrophobic and oleophilic characteristics. The oil sorption by SP was ascribed to van der Waals forces, and the penetration of oil may be due to capillary action (Chu & Pan, 2012). Generally, roughness and low surface energy contributed to the superhydrophobicity. So the surface roughness of RP increased by acetylation method or coating with PS polymer.