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Aqueous Solutions of Poly(ethylene oxide): Crossover from Ordinary to Tricritical Behavior
journal contribution
posted on 2016-10-24, 17:50 authored by Dietmar Schwahn, Vitaliy PipichThe 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.