Shear-Sensitive Chain Extension of Poly(ethylene oxide) by Aluminate Ions During Concrete Curing*

Despite a large literature, questions about PEO’s interactions with ions remain. Motivated by PEO’s potential to reduce CO2 emissions as a strength-building concrete additive, its conformation was examined in solutions containing complex ions found during concrete curing. Conformational changes in most electrolytes were unremarkable, hydrodynamic radius by dynamic light scattering and intrinsic viscosity depressed slightly as ion concentrations grew. Trends were different for aluminum-containing ions [at neutral and basic pH, predominately the monovalent hydroxoalmuminate anion Al(OH)4], hydrodynamic radius by the two methods disagreeing: radius by dynamic light scattering was approximately 40% larger than by intrinsic viscosity. We hypothesize weak, attractive ion-mediated chain-chain interactions, and in particular, a weak coupling between hydroxyl end groups (at just one PEO chain end) disrupted by the shearing during intrinsic viscosity measurements. Supporting our hypothesis, hydrodynamic radius by dynamic light scattering fell to the value by intrinsic viscosity when the groups were converted to methoxy groups. The role, if any, of the coupling in concrete curing is unknown.