LIQUID CRYSTALS AS A NONDESTRUCTIVE INSPECTION TOOL, FEASIBILITY STUDY

LIQUID CRYSTALS SHARE PROPERTIES OF BOTH LIQUIDS AND CRYSTALS. MECHANICALLY, THEY RESEMBLE LIQUIDS WITH VISCOSITIES RANGING FROM GLUE TO "SOLID" GLASS. OPTICALLY, THEY EXHIBIT MANY OF THE PROPERTIES OF CRYSTALS AND ALL LIQUID CRYSTALS EXHIBIT BIREFRINGENCE. THE MOLECULAR STRUCTURE OF A CHOLESTERIC LIQUID CRYSTAL IS VERY DELICATELY BALANCED AND CAN BE EASILY UPSET. IN THE CHOLESTERIC LIQUID CRYSTALS THE MOLECULES ARE ARRANGED IN VERY THIN LAYERS. WITH EACH LAYER THE LONG AXES OF THE MOLECULES ARE PARALLED TO THE PLANE OF THE LAYER. THE MOST STRIKING OPTICAL TRANSFORMATION THAT OCCURS IN A CHOLESTERIC SUBSTANCE IN RESPONSE TO SUDDEN CHANGES IN ENVIRONMENT IS THE VARIATION OF COLOR WITH TEMPERATURE. IT IS THIS COLOR RESPONSE OR CHANGE OVER TO THE VISIBLE SPECTRUM WITH TEMPERATURE THAT HAS AROUSED INTEREST IN CHOLESTERIC LIQUID CRYSTALS AS A POSSIBLE NON-DESTRUCTIVE INSPECTION TOOL. AT A GIVEN TEMPERATURE, A GIVEN MATERIAL OR COMBINATION OF CHOLESTERIC MATERIALS WILL ALWAYS EXHIBIT THE SAME COLOR. THE RATE OF CHANGE FROM COLOR TO COLOR AS WELL AS THE EXACT TEMPERATURE AT WHICH A SPECIFIC COLOR OCCURS ARE INVARIABLE. THIS FEASIBILITY STUDY CONSISTED OF A LITERATURE SURVEY AND VISITS TO ACTIVITIES USING LIQUID CRYSTALS. LIQUID CRYSTALS WERE FOUND TO HAVE A DEFINITE PLACE IN NON-DESTRUCTIVE INSPECTION OF AIRCRAFT PARTS, PROVIDED THERMAL CONDUCTIVITY OR THE LACK OF IT CAN BE EMPLOYED FOR INSPECTION PURPOSES. CHEMICAL VAPORS DEVELOP THE COLOR RESPONSE IN LIQUID CRYSTALS SIMILAR TO THAT PRODUCED BY TEMPERATURE. MECHANICAL STRESS CAN ALTER THE MOLECULAR STRUCTURE OF CHOLESTERIC MATERIALS AND HENCE THE COLOR-REFLECTING PROPERTIES. ELECTROMAGNETIC RADIATION CAN ALSO AFFECT THE CHOLESTERIC LIQUID CRYSTALLINE STRUCTURE TO PRODUCE COLOR CHANGES AND OFTEN UNIQUE TEXTURAL PATTERNS.

• Supplemental Notes:
  • Rept No NaeC-AML-2634, 16 PP, FIGS, 8 REF
• Corporate Authors:

  Naval Air Engineering Center /US

  ,    
• Authors:
  • Erthal, J F
• Publication Date: 1967-6

Subject/Index Terms

• TRT Terms: Color; Electromagnetic waves; Liquids; Molecular structure; Nondestructive tests; Optical properties; Refraction; Reviews; Rock crystals; Temperature; Thermal conductivity
• Uncontrolled Terms: Change
• Old TRIS Terms: Birefringence; Cholesteric materials
• Subject Areas: Geotechnology; Highways; Materials;

Filing Info

• Accession Number: 00217020
• Record Type: Publication
• Files: TRIS
• Created Date: Oct 19 1970 12:00AM