Surface fogging induced degradation has been a bottleneck problem in potassium dihydrogen phosphate (KDP) crystals due to they are grown from aqueous solution. In this paper, we developed a facile method to prepare a double-layer antireflective coating with moisture-proof and laser damage resistant properties for KDP crystals. The bottom layer was a poly siloxane coating with dense structure and silanol side groups, while the top layer was a hexamethyl-disilazane (HMDS) modified nanoporous SiO coating. Both of the sols were nonalkaline and nonaqueous to make sure those are harmless to KDP crystals. The double-layer coated KDP crystal exhibited a maximum transmittance of 99.9% with an average increase of transmitted light of 6-7% over the wavelength range between 351 and 1053 nm. After exposure in a 55% relative humidity environment for 6 months, the double-layer HMDS_SiO/PS coating coated KDP crystal displayed nearly the same optical transmittance as the original one, whereas the single-layer HMDS_SiO coated KDP crystal had a transmittance loss of ∼5%. Moreover, the laser-induced damage threshold of the double-layer coating on KDP crystal reached 11.5 J/cm (355 nm, 3 ns). This multifunctional antireflective coating not only can be used for KDP crystals, but also can be applied to thermal-sensitive polymeric substrates.
Mechanical and contamination-resistant
properties are the most crucial and challenging issues that impede
the practical applications of sol–gel antireflective (AR) coating.
In this paper, we report a low-temperature vapor surface treatment
strategy for the partial embedding and surface functionalization of
silica nanoparticles (SNPs) on flexible polymeric glass substrates.
SNPs, which were synthesized via the Stöber method, were partially
embedded into the polymeric glass substrates by vapor-phase surface
treatment using volatile chloroform. Further vapor-phase surface treatments
by water and hexamethyldisilazane (HMDS) were applied successively
to achieve high trimethylsilyl coverage of the SNPs. The HMDS modification
could convert the polar surface of SNPs to a nonpolar surface for
contamination resistance, while ammonia, as a byproduct generated,
could help to cross-link the SNPs via self-condensation of silanol
groups, thus hardening the coating. The SNP-CWH coated polymethylmethacrylate
(PMMA) substrate shows an average transmittance of 98.62% in the wavelength
region of 400–800 nm, which is 6.32% higher than that of the
uncoated bare PMMA. The AR performance of SNP-CWH coated PMMA shows
almost no degradation after 100 times of rubbing or bending, indicating
the greatly enhanced abrasion resistance and flexibility. Furthermore,
the SNP-CWH coating exhibits superior contamination-resistant property,
where the transmittance curve of the coated substrate displays a barely
noticeable change after exposure to a “dirty” environment
with water and organic contaminants for 6 months. This work paves
a new way for developing mechanically robust and contamination-resistant
AR coating for polymeric substrates.
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