Superhydrophilic and Antireflective Properties of Silica Nanoparticle Coatings Fabricated via Layer-by-Layer Assembly and Postcalcination

Superhydrophilic and antireflective coatings were fabricated from silica nanoparticles of 30 nm (S-30) and 150 nm (S-150) and polyelectrolytes of poly(diallyldimethylammonium) chloride (PDDA) and sodium poly(4-styrenesulfonate) (PSS) via layer-by-layer assembly and postcalcination. The time for a droplet to spread flat decreases to as short as 0.28 s by applying a coating of (PDDA/S-150)(3)/(PDDA/S-30)(2) while the maximum transmittance reaches as high as 98.5% by applying a coating of (PDDA/S-30)s. Factors that affect the superhydrophilic and antireflective properties of coatings, such as the number of deposition cycles, size of nanoparticles and surface toughness, were investigated in details by observing their surface morphologies and by measuring their water contact angles, water spreading time, and transmittances. Systematic investigation gave an optimal structure of calcinated (PDDA/S-30)(8)/(PDDA/S-150)(2)/(PDDA/S-30)(2) for the superhydrophilic and antireflective coating. Its maximum transmittance and the time for a droplet to spread flat reached 97.1% and <0.5 s, respectively, indicating that both antireflective and superhydrophilic properties were achieved by a single coating. Finally, the roles of S-30 and S-150 nanoparticles in enhancing the superhydrophilic antireflective properties were discussed.