Glass Transitions in Hydrated Polyelectrolyte Complexes
Yuhui Chen, Mo Yang, Joseph B. Schlenoff
Abstract
The spontaneous association of oppositely charged natural or synthetic polyelectrolytes in solution has evoked a great deal of interest from chemical, physical, and biological perspectives. The polymer-dense phases resulting from this phase separation are termed polyelectrolyte complexes or coacervates, PECs. PECs exhibit a range of properties and morphologies, from liquidlike to solidlike states. Though PECs have high water contents, a few of them are known to exhibit a glass transition near room temperature. In this work, the library of glassy PECs is substantially expanded with compositions that exhibit glass transition temperatures, Tg, over the entire working range of aqueous solutions between 0 and 100 °C. A radiochemical method of measuring the volume of pores that usually form in glassy PECs enabled a comparison of Tg with PEC phase water volume fraction, ϕH2O,PEC. Tg correlated weakly with ϕH2O,PEC only for a series of PECs in which one of the polyelectrolytes was held constant. In general, Tg was poorly correlated with ϕH2O,PEC. On the other hand, time–temperature superposition of linear viscoelastic responses provided a classical estimate of fractional free volume of PECs, which correlated well with Tg.