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