Construction of a Microprocessor-Controlled Film Balance

A fully microprocessor-controlled film balance and a film lift system were constructed (Fig. 3). The speed of the moving barrier, which is driven by a vibration-free pulse motor system coupled with linear ball bearing and threaded screw (2 mm pich) (Fig. 1), is changeable from 0.04 mm/s to 8 mm/s. The resolution and the accuracy of the barrier position are 40 pm. Feed-back control from a pressure sensor (Wilhelmy plate system using a load cell sensor) enables measurement of pressure-area isotherms by the pressure-equilibration mode (Fig. 5). The isotherm of stearic acid obtained by this mode was different from that of the constant-speed mode (Fig. 6). The vibration-free film lift, driven by a timing belt-pulse motor system (Fig. 2), and the high resolution (0.03 mN/m) of the pressure sensor are effective for preparation of LB films with good quality. All data and conditions are transferred to a personal computer through the RS 232 C communication interface and analyzed by a BASIC program. Changeable control parameters enable measurements un,der precisely-set conditions.