Effects of nanobubbles on the physicochemical properties of water: The basis for peculiar properties of water containing nanobubbles

Abstract

The mechanism with which nanobubbles (NBs) promote physiological activity is investigated using germination tests and nuclear magnetic resonance (NMR) relaxation-time measurements. The germination rates of barley seeds dipped in water containing NBs (bubbles formed from gas mixtures of nitrogen and pure air) were 15–25 percentage points greater than those of the seed dipped in distilled water with the same concentration of dissolved oxygen (DO). In addition, the proton NMR relaxation time, T2, of water containing NBs (bubbles formed from nitrogen) was measured and compared with the T2 of control water (water without bubbles or DO). After T2 measurements, both water containing NBs and control water were degassed, and the T2 values were subsequently measured again to examine its changes before and after degassing. Water containing NBs exhibited T2 values that were statistically longer than those of control water. After degassing, the T2 values of water containing NBs decreased, which indicated that the decrease in the NB number density shortened T2. On the basis of these results, we concluded that the number of NBs was positively correlated with the T2 value of the water. The increase in T2 with the generation of NBs indicated that the mobility of the water molecules increased; consequently, a longer time was required to reach the equilibrium state through spin–spin relaxation. These observations indicated that the NBs in water could influence the physical properties of water and that it could also be used to verify the stability of NBs in the water.