Coating of polymethylmethacrylate with transparent SiO2 thin films by a sol-gel method

In order to improve the surface characteristics of polymethylmethacrylate (PMMA), oxide thin-film coatings were applied using the sol-gel dip-coating technique. Si(OC2H5)4 (TEOS), CH3Si(OC2H5)3 (MTES) OR Ti(O-i-C3H7)4 (TIP) was used as a starting material for SiO2 or TiO2 coating. The hardness of the alkoxy-derived oxide-coated PMMA was increased from 200 MPa for non-coated PMMA with increasing film thickness. By optimising the heating conditions and the hydrolysis conditions, and by repeating the dip-coating/heating processes, a hardness as high as 325 MPa was achieved for PMMA triply coated with the TEOS-derived SiO2 film using the withdrawal velocity of 0.30 mm/s and heat treatment at 80 C. The increase in hardness with the thickness of coating film was saturated before reaching that of bulk silica-dried gel (about 500 MPa), which may be due to the increased porous nature of the thick films. 11 refs.