Construction of a Microprocessor-Controlled Film Balance

Abstract

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 μm. Feed-back con trol 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 constantspeed 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 under precisely-set conditjons.