Macro- and microscale rheological properties of poly(vinyl alcohol) aqueous solutions

Electric conductivity measurements indicated that microviscosities of poly(vinyl alcohol), PVA, solutions [up to 10% (w/w)] are comparable to that of pure water (contrary to Walden's rule), but are different (25%) from those determined from diffusion-controlled reaction measurements that coincide with the values obtained using pure water. Energies of activation of fluidity of PVA solutions are found to increase with PVA concentration, whereas those of the diffusion-controlled reactions are independent of PVA concentration. By comparing the macro- and microviscosities, it was concluded that PVA aqueous solutions can be envisioned as dynamic systems comprising hydrated PVA molecules (that affect the macroviscosity) and "interconnected water pools" (located between macromolecules), the rheological properties of which are very similar to that of pure water. Fluorescence depolarization measurements indicated that pool sizes are relatively large, which was corroborated by DSC measurements that showed that each PVA hydroxyl group interacts with no more than two water molecules.