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