Influence of chain length on the α-β bifurcation in oligomeric glass formers -: art. no. 165701

A series of oligo(propylene glycol) dimethyl ethers has been investigated using dielectric spectroscopy in order to relate features of the glass transition dynamics to the number of monomer units N in the chain. The results show that (i) when scaled with the glass transition temperature, the beta relaxations systematically become faster for larger N whereas the alpha relaxations display nearly identical temperature evolutions, i.e., the alpha-beta bifurcation shifts towards shorter times for larger N, (ii) the bifurcation scenario displays a crossover in behavior at N similar to 10 monomer units, signaling the transition from oligomeric to polymeric behavior, and (iii) the beta relaxation has a cooperative nature.