ABSENCE OF ANNEALING EFFECT IN THE VIBRATIONAL DENSITY-OF-STATES IN AGLASSFORMING POLYMER

We describe experiments devised to detect a possible effect of anneali ng on the vibrational density of states (DOS) in a glassforming polyme r with high accuracy from inelastic incoherent neutron scattering. Suc h an effect could be expected from the argument that annealing changes the behavior of many measured quantities, especially the specific hea t c(p)(T). For the experiment polybutadiene was chosen because the eff ect on c(p)(T) as well as the optimal conditions of annealing are well known for this material. Contrary to our expectations an annealing ef fect could be detected neither in the inelastic spectra taken on IN6 n or in the elastic scans performed on IN16 at ILL, Grenoble. From this we conclude that the observed annealing effect on c(p)(T) does not ori ginate from a difference in the DOS but rather from other sources, e.g , a change of configurational entropy. This result is in agreement wit h a theory of DiMarzio which gives a good prediction of the step Delta c(p) at the glass transition in the case of polybutadiene and attribu tes only 8%-10% of it to vibrational terms. (C) 1998 American Institut e of Physics.