Insight into clustering in poly(ethylene oxide) solutions

The clustering phenomenon has been observed in many macromolecular systems. Poly(ethylene oxide) solutions are characterized by a clustering effect that has been extensively discussed in the literature. Its origin has remained elusive. Using small-angle neutron scattering from PEO solutions in various deuterated solvents, the possible causes of clustering that have been given in the literature are analyzed here. These include impurities in water, possible PEO crystallization, a subtle phase transition whereby a concentrated phase coexists with free polymer coils, hydrogen-bond physical crosslinking, and finally chain ends effect. We have shown that under the experimental conditions considered here (4% PEO weight fraction) the mostly forgotten chain ends effect is at the origin of clustering in poly(ethylene oxide) solutions.