Accession Number : ADA263737


Title :   Molecular Dynamics of Physical Aging Processes in Polymer Glasses


Descriptive Note : Final rept. Jan 1990-Dec 1992


Corporate Author : CASE WESTERN RESERVE UNIV CLEVELAND OH


Personal Author(s) : McGervey, J D


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a263737.pdf


Report Date : 23 Feb 1993


Pagination or Media Count : 3


Abstract : We have used the positron as a microscopic probe to clarify the connection between the microscopic properties (e.g., free volume distributions) and macroscopic properties (pressure, volume, and temperature relations) of polymers in the glassy state. Measurements of the positron lifetime distribution in the polymer as a function of temperature, aging, and applied strain have shown that positrons are sensitive to the distribution of free volume elements. However, we have also found that refinements in data analysis are necessary, and that we are far from obtaining an unambiguous free-volume distribution from the current results. Theoretical models are being tested to see if they are consistent with the results. We have also generated simulated positron lifetime distributions to test the validity of our curve-fitting methods, and we have discovered that these methods break down when the instrumental resolution curve exceeds approximately 250 nanoseconds, in width.


Descriptors :   *AGING(MATERIALS) , *DYNAMICS , *GLASS , *MOLECULAR PROPERTIES , *POLYMERS , ANNIHILATION RADIATION , CURVE FITTING , DISTRIBUTION , FITTINGS , FUNCTIONS , MEASUREMENT , MODELS , POSITRONS , PRESSURE , PROBES , RESOLUTION , STRAIN(MECHANICS) , TEMPERATURE , TEST AND EVALUATION , VOLUME , WIDTH


Subject Categories : Polymer Chemistry
      Atomic and Molecular Physics and Spectroscopy
      Nuclear Physics & Elementary Particle Physics
      Mechanics


Distribution Statement : APPROVED FOR PUBLIC RELEASE