Modern Polymer Spect..

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Figure 3-59. Time-dependent infrared spectruni in the 960-900 cm-’ range showing the Pi5 component
of the CHz rocking progression band of n-CrlH44 and the P17 component of n-Cr3HdZ.
Evolution with annealing time. Annealing temperature 30T, A(t = 0); B (t = I hr); C (t = 2 h); D
(t = 4 h); E (t = 6 h). At t = 0 the sample consists of a mechanical mixture of the two materials. At
t = 0 both solids are crystalline orthorhombic as shown by the correlation field splitting doublet. By
increasing the time of annealing both doublets coalesce into a singlet indicating that chains have
migrated and formed a mixed crystal.
Figure 3-60 shows the kinds of kinetic studies of the mixing process which have
been made.
Conclusion no. 6
In the a phase chains move longitudinally and are ‘squeezed out of the lamella’; the
onset of such motion occurs near the solid-solid transition temperature.
This is in agreement with recent measurements of quasi-elastic neutron scattering
by Gullaume et al. on C19 at 300°K who determined the existence of translational
longitudinal diffusion with discrete steps of one or two CH2 units with a measured
diffusion coefficient D = 6 x lop6 cm’s-l [157]. Statistical thermodynamics calculations
give theoretical support to this kind of phenomenon [ 1581. These conclusions
find a striking support by the calculations of molecular dynamics by Klein [159]
which describe precisely all the details that we have found from spectroscopy.
Moreover, recent experiments of temperature-dependent scanning tunnelling microscopy
by Rabe et al. [160] give just ‘photographic’ support at the molecular level of
the process as described by spectroscopy, namely: (i) first the chains organized in
an ordered lattice; (ii) then the onset of longitudinal diffusion which generates