Cluster cooperative motion

All protic solvents undergo multiple relaxation processes due to the presence of hydrogen bonding. In the case of water and formamide (F), the data can be described in terms of two Debye relaxations. For the alcohols and A-methyl-formamide (NMF), three Debye relaxations are required for the description. In all of these solvents, the low-frequency process involves the cooperative motion of hydrogen-bonded clusters. In the case of water and the alcohols the high-frequency process involves the formation and breaking of hydrogen bonds. The intermediate process in the alcohols is ascribed to rotational diffusion of monomers. Studies of dielectric relaxation in these systems have been carried out for the -alkyl alcohols up to dodecanol [8]. Values of the relaxation parameters for water and the lower alcohols are summarized in table 4.5. 

F and NMF are also highly structured solvents as a result of hydrogen bonding. The low-frequency relaxation process in these systems can be attributed to the cooperative motion of hydrogen-bonded clusters. The process at the highest frequencies has a similar relaxation time to those observed in DMF and DMA. Thus, it is probably due to intramolecular rotation about the C-N bond in the monomer. The intermediate relaxation observed in NMF is attributed to rotational diffusion of a monomer. Relaxation parameters for F and NMF are also summarized in table 4.5. 

The normal explanation for specific heat deviation above Tg as effect of crystallization or melting can not be used here. A possible explanation of the observed data could Involve cluster formation. The reported specific heat and volume data Indicate structural changes in the glassy state with different mobilities nonequilibrium vitrification process and altered by the following thermal treatment of the samples. This process, an alteration of cooperative motions due to cluster formation, leads to a decrease in mobility of the chains and prevents equilibrium enthalpies above Tg to be directly attained at the selected scanning rate. 

For percolating microemulsions, the second and the third types of relaxation processes characterize the collective dynamics in the system and are of a cooperative nature. The dynamics of the second type may be associated with the transfer of an excitation caused by the transport of electrical charges within the clusters in the percolation region. The relaxation processes of the third type are caused by rearrangements of the clusters and are associated with various types of droplet and cluster motions, such as translations, rotations, collisions, fusion, and fission [113,143]. 

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