Dielectric study on two dynamic phases of 1-propanol confined in mesopores of MCM-41

Two dynamic phases were recognized on the 1-propanol molecules confined in MCM-41 with pore diameters d = 2.1, 2.4, 2.7 and 3.6 nm by dielectric measurements, in which two types of confined states of liquid were investigated: surface-adsorbed (sa) and pore-filled (pf) liquid. The dielectric measurements in the frequency range 103–107 Hz and temperature range 120–300 K showed that the molecular motions became slower in the following order: bulk, pf and sa liquid, which is the same order as for methanol and ethanol confined in MCM-41 reported previously. For pf samples, two relaxation components, which correspond to molecules near the pore surface and at the center of the pores, were observed separately. This is somewhat different from the behavior of methanol and ethanol confined as pf state in which two relaxation components were also detected but a clear separation between them was not observed. This implies that 1-propanol molecules near the pore wall interact weakly with those at the central part of the pores. For the MCM-41 sample with the smallest pore diameter (d = 2.1 nm), however, the dielectric spectra of the pf sample were very similar to those of the sa sample. That is, the dynamic motion of molecules in the pf sample was inhibited by narrow space surrounded by monolayer molecules similarly to that in the sa sample