Comparison of superhydrophobic biodegradable PLA films with fluorine-free hexamethyldisilazane grafted silica and mesoporous silica particles

Abstract

This study reports the surface coating of fluorine-free hexamethyldisilazane (HMDS) on non-porous silica particles (SPs) and mesoporous silica particles (MSPs), with nanopores arranged in the straight channels, and compares the degree of superhydrophobicity by coating them on biodegradable PLA film by gravure process. The particle sizes of SPs and MSPs are 50 nm and 800 nm, and the amount of HMDS grafted onto SPs and MSPs is 0.5% and 9.5%, respectively. The superhydrophobicity of these particles is confirmed by the measurement of water contact angle (WCA) as a function of HMDS concentration for SPs and MSPs from 0 to 1.6 M, respectively. The WCA of HMDS@SPs and HMDS@MSPs grafted with 1.6 M of HMDS is 152° and 151° (WCA of unmodified SPs and MSPs is 13.85° and 27.65°). To apply superhydrophobic PLA film coating, 5 wt% of HMDS@SPs and HMDS@MSPs were mixed with gravure solution and then coated on biodegradable polylactic acid (PLA) film. The results showed that the WCA of PLA film with HMDS@SPs and HMDS@MSPs were 98.40° and 152.31°, respectively. This remarkable difference in WCA is due to the dissociation of HMDS molecules grafted on the surface of SPs and MSPs, which are easily separated by the gravure solvent. For MSPs materials composed of many nanopores, the dissociated HMDS molecules are initially released into the solution but are retained within the nanopores. Therefore, the residual amount of HMDS molecules dissociated by the gravure solution is much higher in HMDS@MSPs than in HMDS@SPs.

Keywords

• Superhydrophobicity
• Hexamethyldisilazane
• Fluorine-free
• Mesoporous silica
• Contact angles
• PLA film