Spin-Probe Study on the Dynamics and Distribution of Solution Molecules in the Nano-Channel of MCM-41

The ESR spectrum of a spin-probe in 2-propanol, which was condensed into the nano-channel of MCM-41 from its vapor, showed three well-separated nitrogen hyperfine lines. This observation indicates that the system exists in the liquid state in the nano-channel, though the rotational diffusion of the spin probe molecule is considerably suppressed and anisotropic. In a mixed solvent composed of 2-propanol and cyclohexane, on the other hand, the ESR spectrum for the system prepared by the above procedure comprised two components, indicating that the solution is phase-separated in the nano-channel. When all of the space in the MCM-41 layer, including that among the granules, is filled with the solution, the molecules obtain a higher mobility and phase separation is suppressed even in the nano-channel. The distribution and dynamics of the solution molecules are discussed.