HYDRATION WATER DYNAMICS IN UNDERCOOLED AQUEOUS-SOLUTIONS OF HYDROPHOBIC IONS

Deuterium spin-lattice relaxation times (H-2 T1) are reported for the first time as a function of temperature (180-300 K), pressure (p less-than-or-equal-to 225 MPa), and composition (c less-than-or-equal-to 5 m) in undercooled aqueous solutions of tetraalkylammonium ions (R4N+). A comparison with related investigations of undercooled alkali-metal halide solutions allows the competing influence of coulombic, hydrophobic, and H-bond interactions upon the dynamic structure of the random, transient H-bond network to be studied. Solvent dynamics are seen to be closely related to the glass-forming tendency of undercooled tetramethylammonium (Me4N+) and tetrapropylammonium (Pr4N+) bromide solutions and to the clathrate-forming tendency of undercooled tetrabutylammonium (Bu4N+) bromide solutions.