Low-frequency mechanical spectroscopy study of conformational transition of polymer chains in concentrated solutions.

A low-frequency mechanical spectroscopy approach for liquids was proposed for studying conformational transition of polymer chains in concentrated solutions. The technique is applied to aqueous solutions of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer in order to determine if chain conformation is altered in response to temperature. Two transitions are revealed by mechanical spectra and verified by differential thermal analysis with increasing temperature, which may be related to the unimer-to-micelle transition and the phase separation, respectively. The transitions are also found to be much dependent on the concentration of the solution and the addition of NaCl. Moreover, it reveals that the PEO blocks play a more important role in the micellar crystallization process. This study may be helpful in understanding the dynamics of polymer chains in concentrated solutions.