This study examines the structural transition between plasma-polymerized silicon-oxide (SiOx) and silicon-organic (SiOCH) coatings with varying organic content. Using comprehensive characterization techniques on 13 samples with systematically varied oxygen-to-hexamethyldisiloxane ratios and energy densities, we found that SiOx barrier coatings unexpectedly exhibited higher porosity than SiOCH coatings. This suggests chemical composition impacts barrier performance more than nanopore structure. The transition from SiOCH to SiOx involves molecular-level structural reorganization, likely due to absent Si-C bonds in SiOx coatings, creating a more rigid SiO₂-like cage structure. These findings provide crucial insights into structure-property relationships of silicon-based plasma coatings, essential for optimizing gas barrier functionality in applications like food packaging.
Franke et al. (Wed,) studied this question.