Aqueous Solutions of Poly(ethylene oxide): Crossover from Ordinary to Tricritical Behavior

2016-10-24T17:50:10Z (GMT) by Dietmar Schwahn Vitaliy Pipich
The aqueous associating solution poly­(ethylene oxide) (PEO) of molar mass between 0.45 and 280 kDa was studied with small-angle neutron scattering (SANS) near their critical concentration in a temperature interval from 11.8 to 95.7 °C. SANS measures thermal concentration fluctuations whose susceptibility and correlation length identified mean-field, 3D-Ising, and tricritical Θ-point critical behavior. Scaling laws of the critical amplitudes of susceptibility and correlation length were observed for the samples obeying 3D-Ising and tricritical Θ-point behavior in agreement with the predicted ones for nonassociating semidilute solutions. On the other hand, chain conformation is different for both classes of criticality and is attributed to the concentrated and semidilute regime of the phase diagram. In the concentrated regime the chains are slightly more compacted than Gaussian coils. However, all PEO solutions approach ideal chain conformation at the Θ-temperature. A small amount of PEO of the order of 10–5 is forming compact PEO aggregates.