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Dynamic Mechanical Analysis of Cryogenic Target Materials

Adhesive strength is of critical importance for cryogenic laser-fusion targets when bonding the plasma-polymerized polystyrene copolymer plastic target shell to the support stalk (a narrow-diameter fiber of silicon carbide or Zylon PBO). Norland 68 and Dymax 921 gel, two rapid-curing, low-to-medium viscosity UV curable adhesives, are currently used for target fabrication depending on which fiber material is employed. Neither of these adhesives is rated for operation at cryogenic temperatures, and the interfacial bonding strength of these adhesives to the target shell has not been thoroughly characterized, other than through in-use testing. To compare the interfacial strengths of these two adhesives, a sample preparation method involving a polystyrene loop glued to a polystyrene strip was developed and tested with a Perkin Elmer DMA8000 dynamic mechanical analyzer. This instrument is capable of determining mechanical properties over a wide range of temperatures and dynamic loads. Although results showed some scatter in adhesive-strength data points for both Norland 68 and Dymax 921 gel at cryogenic temperatures, test runs revealed that a decrease in temperature resulted in an increase in interfacial bond strength between the adhesives and the polystyrene. Further research in sample preparation could lead to more consistent results.