Effect of self-bias voltage on the nanoscale morphological properties of corn starch-based films modified by hexamethyldisiloxane plasma

Abstract

Thermoplastic starch (TPS) films underwent casting and plasma coating with Hexamethyldisiloxane (HMDSO) gas at various self-bias voltages. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) imaging revealed slight swelling and grain structures in untreated TPS films due to starch dissolution. However, the HMDSO plasma treatment had minimal impact, with swollen grains still present beneath a layer of small granules. Contact angle measurements demonstrated that untreated films had an initial water contact angle of 32°, gradually decreasing over time. Conversely, HMDSO-coated films exhibited stable hydrophobic behavior, with contact angles exceeding 100°. Statistical analysis confirmed TPS films’ lower average roughness, while modified films showed no significant difference in height parameters. Higher self-bias voltages correlated with larger grain sizes. Notably, experimental treatments decreased long-range spatial correlations, as indicated by Hurst's exponent.