Chemical analysis of a cornstarch film surface modified by SF6 plasma treatment

SF6 plasmas were employed to improve the water repellency of cornstarch films by producing physical as well as chemical modifications of the film surface. Samples were placed in the cathode of a capacitively coupled plasma enhanced chemical vapor deposition (PECVD) reactor. Local surface modifications resulting from SF6 plasma treatment were evaluated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Photoelectron spectroscopy (XPS) and Raman spectroscopy were used to characterize sulfur and fluoride incorporation on the surface as well as changes in the chemical state of carbon. The results indicate that fluoride and sulfur incorporation is dependent on the self bias, and fluoride is preferentially incorporated at self-biases higher than 100 V. The carbon chemical state changed, and an amorphous-like layer was formed upon treatment. Surface reticulation was observed, indicated by the formation of a structure that resembled starch recrystallization. Optimized treatment conditions led to water contact angles over 120°.