Alpha, Beta and Gamma Transitions

In the dynamic mechanical loss spectra of polymers, the transitions that are related to different molecular motions within polymers are called a, 3 and y transitions. 

The a transition involves long segments of the polymer chain where the movement causes other chain segments to move out of the way. These cooperative main-chain motions are increasingly prevalent at the Tg and can be used to define the Tg of a material. 

The P transition involves chain segments that are shorter than those in a transitions. For that reason, they occur below the Tg of the material. 

The motion producing the y transition involves short chain segments. In many polymeric systems, the y transition is caused by the crankshaft rotation of the methylene (-CH2-) groups on a long polymer chain. Since the y transition involves those molecular segments, it occurs helow the a and P transitions. 

Six techniques have been used to detect transitions other than Tg in polymers. These include DTA, DMA, DETA, infrared (IR) spectroscopy, DSC and TMA. 

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Figure 13.4 Shear storage modulus - temperature plot for semi-crystalline 6,6 Nylon demonstrating alpha, beta and gamma transitions. Source Author s own files)...

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