Effects of Radiation-Induced Cross-Links on the Low-Temperature Thermal Properties of Polystyrene

Abstract
Measurements of the thermal conductivity and heat capacity in the liquid‐helium temperature range of polystyrene which was cross linked by exposure to an 80‐MeV electron beam are reported. The measurements were performed over a range of cross‐linking coefficient from 0 to 12. No significant change in the thermal conductivity was observed, but about a 25% reduction in the heat capacity occurred. The thermal conductivity results are compatible with the existing theory of the thermal conductivity of amorphous polymers, while the heat capacity result is taken to indicate a significant reduction in the ``excess heat capacity'' associated with nonacoustic, low‐frequency modes.

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