Perhaps you should try some spelling variations:
22optical materialss » optical material, optic materials, optics materials
acoustical materials » acoustic materials, acoustic material, classical materials
critical materials » chemical materials, artificial materials, frictional 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 materialss) OR (optical materials))) OR (((acoustical materials) OR (critical materials))))%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%((((22optical materialss) or (optical materials))) or (((acoustical materials) OR (critical materials))))%22".
• Adding a wildcard symbol may retrieve word variants: %((((22optical materialss) or (optical materials))) or (((acoustical materials) OR (critical materials))))%22*.