I want to have a thin coating (a few microns) of titanium dioxide on a plastic plate, to make high refractive index surface. Assuming titanium dioxide is in powder form, can I mix the powder with some liquid resin to apply on the plate?
Is there any ready-to-apply titanium dioxide in  liquid form?  Thanks.
       Peter
        

Titanium dioxide powder applied in liquid resin = white paint.

You will need to use a Physical Vapor Deposition (PVD) process requiring a vaccum system. Evaporation is easiest, but requires a minimum substrate temperature of 250^oC for optical coatings. http://www.cerac.com/pubs/proddata/tio.htm
 
Since this temperature is too high for most plastics, you may need to deposit via sputtering.  Find a vacuum coatings vendor.

Some more info.  This is possible with the right nano particles of titanium dioxide.  
Colorscience uses TiO₂ particles ~50 nanometers (0.05 micron) in a clear sunscreen 'Sunforgettable' and cosmetics. The supplier & technical details, such as the the degree of opacity of the particles prior to wetting by the carrier liquid, are not disclosed.
http://www.colorescience.com/800x600/flash/index.html

A scientific abstract mentions TiO₂ nano particles coated with a film of silica:  http://nanodot.org/article.pl?sid=02/08/02/0752217
The supplier is Shenzhen Chengyin Technology http://www.chengying.com/product-nme.htm
It seems that the TiO₂ particles (available in av. sizes 50 & 25 nm) are white, but the liquid, perhaps with the aid of the silica film coating, makes the overall dispersion appearance 'Liliquoid.'

Not your ordinary TiO₂ particles! Seems worth investigating.  Good luck, and please post any results.
Ken

Thanks for the information. For my application the white paint may be good enough.