Effect of plastics substrate on phase separation behavior and adhesion for RSi(OC2H5)3–Si(OC2H5)4 coatings prepared by sol–gel process

Three functional siliconalkoxides (RSi(OC2H5)3, RTES), phenyltriethoxysilane (PhTES), methyltriethoxysilane (MeTES), and 1,4-bis(triethoxysilyl)benzene (BTEB)–tetraethoxysilane (Si(OC2H5)4, TEOS) coatings [xA−(100−x)TEOS (x=0–80, mol%), A=PhTES, MeTES, BTEB] were prepared by sol–gel process, and the effects of plastics substrates on both the distribution of organic component in the coatings and its adhesion on plastics substrates were discussed. Polyethylene terephthalate (PET) and polycarbonate (PC) with phenyl group and polyethylene (PE), polypropylene (PP) and polyvinylchloride (PVC) without phenyl group were employed as plastics substrates. The distribution of organic component was monitored by total reflection (ATR) fourier transform infrared (FTIR) measurements. Before the solidification of the coating sol, the organic component for good adhesion migrated on coatings/substrate interface side by the interaction between organic component and substrate. This interaction may be caused by π/π electron interaction, CH3/π electron interaction and CH3/CH3 van der Waals interaction. The migration of phenyl group on plastics substrate with phenyl group was larger than that on plastics substrate without phenyl group, while the migration of methyl group on plastics substrate without phenyl group was larger than that on plastics' substrates with phenyl group. Thus, the chemical structure of substrate affected phase separation behavior in the coatings. Adhesion of PhTES–TEOS and BTEB–TEOS coatings on PET and PC increased drastically at larger than x=60. On the other hand, no adhesion was observed for all the MeTES–TEOS coatings.