Local density augmentation of supercritical water probed by 4,4′-bpyH[rad] radical: A pulse radiolysis study

Abstract

Solvatochromic shift of 4,4′-bpyH in aqueous solutions at elevated temperatures up to supercritical conditions and in various organic solvents with different dielectric constants, is investigated by pulse-radiolysis technique. 4,4′-bpyH shows a stronger solvent–solute interaction in water than in organic solvents, perhaps due to the hydrogen bond between 4,4′-bpyH and water. At 380°C, local density augmentation, namely ρlocal–ρbulk, in supercritical water becomes 280kgm−3 (ρbulk=208kgm−3), and the density enhancement factor is 8.9. Density fluctuation maximizes when ρbulk is around 120kgm−3. Density inhomogeneity decreases as temperature rises, but is still remarkable at 400°C.