2. Materials and methods
2.1. Drying apparatus and procedure
An outline of the experimental apparatus is presented in Fig. 1. A
drying chamber was constructed from a glass tube with an inner
diameter of 65 mm. A vacuum pump (oil-sealed vacuum pump,
GLD-136C, ULVAC KIKO Inc.) along with a pressure-control valve
was used to control the pressure in the drying chamber. The
pressure was controlled at a reduced pressure of 12 ± 0.5 kPa. A
pressure transducer (BARATORON®, Type 631, MKS Instruments,
Inc.) and an indicator (indicator; Type 250, MKS Instruments, Inc.)
were used to measure the pressure.