Perhaps you should try some spelling variations:
22optical materials » optical material, acoustical materials, optics materials
critical materials » chemical materials, artificial materials, frictional materials
optic materials » basic materials, ionic materials, organic materials

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: %((((22optical materials) OR (optic materials))) OR (((critical materials) OR (optical materials))))%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%((((22optical materials) OR (optic materials))) or (((critical materials) or (optical materials))))%22".
• Adding a wildcard symbol may retrieve word variants: %((((22optical materials) OR (optic materials))) or (((critical materials) or (optical materials))))%22*.