In-situ thin coating of silica micro/nano-particles on polymeric films and their anti-fogging application

Polymeric films, e.g., polyethylene (PE), coated with a thin layer of silica micro/nano-particles (SiO2 M/NPs) were prepared using a modified Stöber method in the presence of corona treated and non-treated PE films. The obtained films were washed of excess reagents and non-bonded (free) SiO2 M/NPs and dried. Only the corona-treated PE films were coated with a thin layer of SiO2 M/NPs while the non-treated films were almost empty of bound SiO2 particles. PE films composed of bound mesoporous silica NPs were similarly prepared with the addition of cetyltrimethylammonium bromide (CTAB) in the polymerization process. The effect of various polymerization parameters, e.g., tetraethylorthosilicate (TEOS) concentration, ammonium hydroxide concentration and the volume ratio [ethanol]/[water], on the diameter and diameter distribution of the free and surface bound particles were elucidated. Characterization of the SiO2 coated films was accomplished by routine methods such as DLS, HRSEM, water contact angle measurements, AFM and FIB. The SiO2 M/NP coatings on the PE films were found to be durable and did not significantly affect the optical properties of the film. Among the different types of SiO2 coated PE films prepared in our lab only those prepared with CTAB were found to be highly suitable for anti-fogging use. This process of SiO2 coating may be used for many other polymeric films, e.g., PET, PP, PMMA, PC, PVC, etc. as well as for various applications such as superhydrophobic, antimicrobial or UV blocking coatings. This can be done by binding long hydrophobic silane compounds (e.g., octadodecyl trichlorosilane), a positively charged silane compound or a UV absorbing silane, respectively, to the bound SiO2 particle surfaces.