Glass relaxation process correlation

Relaxation Process Correlation by Glass Transition Temperature... 

Due to the dead time, the correlation functions Fcos,sin(rm rp) for short tp cannot be measured with three-pulse sequences, but a further pulse is necessary to refocus the stimulated echo, leading to four-pulse sequences such as (tc/2)x — tp — (n/2) x - tm - (n/2)x - A - (rc/2)y, where the echo forms at a time tp + A after the last pulse.6,102 So far, we assumed x > tp so that molecular dynamics during the evolution time can be neglected. In the studies of relaxation processes in glasses, this assumption is not justified since very broad distributions of correlation times G( 1 n x) exist. Then, it is necessary to explicitly calculate the phases (h, tf) according to Eq. (8) so that, in general, correlation functions resulting from the above four-pulse sequence can be written as... 

They are collective coordinates and, therefore, provide a way to describe phenomena which may show high collectivity like solvation" or vibrational relaxation processes. Collective velocity correlation functions, e.g., have been discussed as indicators for the onset of glass formation. ... 

Hardness measurements such as Rockwell or Vicker s indentation properties are time-dependent as a result of the viscoelastic flow and relaxation processes (236) (see Hardness). Microhardness measurements have been used to correlate with other properties such as Yoimg s modulus and compressive yield stress in polyethylenes (237) and glass-transition temperature of amorphous plastics (238). Scratch resistance in polyproplyene studies was found to have shear yielding as the main cause of plastic flow scratch pattern with tensile tear effects on the surface and shear-induced fracture on the subsurface (239). 

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