Molecular Dynamics of Physical Aging Processes in Polymer Glasses

摘要

We have used the positron as a microscopic probe to clarify the connectionbetween 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.