Preparation of WPU-based super-amphiphobic coatings functionalized by <i>in situ</i> modified SiO_<i>x</i> particles and their anti-biofilm mechanism

Abstract

Fabrication of anti-wetting coatings with anti-biofouling and anti-biofilm properties has become a hot spot of attention in recent years. However, the anti-biofilm mechanism of anti-bacterial adhesion coatings with different wet resistance properties has not been explored in detail. In this work, SiO_<i>x</i> micro-nano particles were prepared by the Stöber method and were <i>in situ</i> modified. The SiO_<i>x</i>/waterborne polyurethane (WPU) coatings were prepared by the drop coating method, and the coatings with different hydrophobic and oleophobic properties were constructed by modifying the process conditions using SiO_<i>x</i> micro-nano particles as the roughness construction factor. Taking the dominant spoilage bacteria of aquatic products, <i>Shewanella putrefaciens</i> as the object, the anti-bacterial adhesion properties and anti-biofilm mechanism of the SiO_<i>x</i>/WPU coatings were investigated. The results show that, with the unmodified SiO_<i>x</i> particles increasing from 1.2% (w/V) to 4.0% (w/V), the hydrophobicity and thermal stability of the SiO_<i>x</i>/WPU coatings are significantly enhanced, but the oil repellency becomes worse due to the mesoporous structure. After SiO_<i>x</i> micro-nano particles are modified with 1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-perfluorooctyl trichlorosilane (PFOTS), the surface energy of the SiO_<i>x</i>/WPU coatings is decreased, the liquid repellency is improved, and the surfaces are rough with the appearance of fluorocarbon compounds, but the thermal stabilities are slightly reduced. Among them, after the secondary modification of SiO_<i>x</i> micro-nano particles, the SiO_<i>x</i>/WPU coatings showed excellent oil repellency, lower surface energies and higher fluorocarbon content on the surface. Particularly, SiO_<i>x</i>/WPU coatings exhibited super-amphiphobicity after adjusting the amount of concentrated ammonia added during the secondary modification process. Meanwhile, we found that for the hydrophobic SiO_<i>x</i>/WPU coatings, the stronger the oleophobic property, the greater the anti-bacterial adhesion ability is, while the anti-bacterial adhesion ability of hydrophobic and selectively oleophobic or superhydrophobic and oleophobic SiO_<i>x</i>/WPU coatings is poor than that of amphiphilic SiO_<i>x</i>/WPU coatings. However, because the super-amphiphobic SiO_<i>x</i>/WPU coatings can be in the Cassie state with the bacterial solution for a long time, it can "capture" enough air to inhibit the irreversible adhesion of the bacteria. More importantly, the coatings can also inhibit the metabolic activity, secretion of extracellular polysaccharides, and activities of ATPase and AKP of the adherent bacteria, so it has a better anti-biofilm property. The anti-biofilm coatings can be used as food packaging materials or coated on the inner surface of packaging boxes to prevent the microbial infection.