Study On The Preparation And Properties Of Hydrophilic Anti-fogging PVA Coating

Fogging on transparent solid surfaces is a common phenomenon in life and manufacture, which is quite disturbing and may even cause great loss. Accordingly, means for eliminating such a disadvantage are urgently required and attempts such as physical heating, coating hydrophilic or hydrophobic component to the surface have been made to impart the anti-fogging property.We developed stepwise surface reactions to graft poly vinyl alcohol to the target surface, which has great adherence and transparency.3-amino-propyl-triethoxy-silane(APTS) was used to prepare an amino-terminated SAM on solid surface(silicon wafer and glass slide), following by successive coatings of PEMA and PVA. Analysis through ATR-FTIR and contact angle goniometry shows successful reactions and grafting in each step. The topography, film thickness and transmittance were characterized using SEM and spectrophotometer. In water durability test, PEMA/PVA coating demonstrates excellent ability to resistant water, which is also a valid proof for the great adherence of the coating.The anti-fogging property of the film was evaluated by several tests under different environmental conditions. Coatings with PEMA and PVA concentration of0.5%,1%and0.5%,1%were found to have better anti-fogging property than others.Anti-fogging time test shows that part of PEMA/PVA(0.5%1%) coating becomes foggy after56seconds being put into moist condition, and209seconds later, all of the coating loses transparency. After adjusting PEMA to0.5%, the partial and complete foggy time becomes78, and393seconds respectively, which indicates great influence of PEMA and PVA concentration on anti-fogging time.Moist air condensation provided direct evidence that the excellent anti-fogging capabilities of the coating was associated with the formation of water sheets as opposed to light-scattering water droplets observed on glass slides. It can be concluded that fogging is indeed the result of the formation of a densely packed collection of water droplets of sufficient size to scatter visible light.Experiments on droplets impacting different surfaces indicated that compared with glass sides, spreading on antifogging coating was greater and as a result less influence to transmittance. This effect is more and more obvious with growing impacting height.