Excellent moisture barrier performance of silicon-doped diamond-like carbon coating for highly hygroscopic polymers

Abstract

Numerous hydrophilic polymer films are not suitable for the deposition of inorganic coating at high temperature to enhance their moisture barrier capabilities due to the risk of deformation and degradation. To address this issue, hollow cathode plasma immersion ion implantation (HCPIII) was employed to deposit both undoped and silicon-doped diamond-like carbon (Si-DLC) coatings onto polymer substrates at temperatures close to ambient. The Si-DLC coating demonstrates significantly improved hydrophobicity, density and reduced internal stress, and superior moisture barrier performance compared to undoped DLC film. The water vapor transmission rate (WVTR) tests revealed that Si-DLC coating achieved a minimum moisture permeability of 3.3 g/m²/day, which was up to 16 times lower than that of polyurethane substrate. Additionally, Si-DLC coating showed excellent adhesive property and abrasion resistance, with no significant loss in moisture barrier even after rigorous abrasion tests. Meanwhile, the barrier performance of Si-DLC remained was almost unaffected after exposure to various corrosive liquids. To further understand the mechanism of water vapor barrier of the materials, molecular dynamics simulation and density functional theory calculations calculation were carried out to verify the number of water molecules adsorptions, adsorption energy, and interaction force between water molecules on different materials. This strategy was finally proved to be highly versatile, applicable to a wide range of hydrophilic polymer substrates, including polymer foam. Given these attributes, Si-DLC coating obtained by HCPIII is poised to offer a promising solution for enhancing the moisture barrier properties of hydrophilic polymer films that are otherwise vulnerable to high-temperature conditions.