Studies of polymer crystal morphology using the raman active longitudinal acoustical mode

In the more than 35 years since the first observation1 of a low frequency Raman-active vibration in short trans chain malkanes whose frequency varied inversely with chain length, there has been a growing interest in the establishment of the longitudinal acoustical mode (LAM) to routinely characterize polymer structure and morphology. When the existence of LAM in polyethylene (PE) was first reported2,3 it became apparent that the fold surface of lamellar crystals (shown in Figure 1) was sufficiently disordered such as to decouple adjacent crystalline stems allowing them to vibrate as independent finite length chain segments. This has given rise to the origin of the acronym LAM, as these accordion modes are referred to in the literature.