ABSTRACT
The apparatus was assembled under a horizontal laminar flow cabinet with zero count of particles greater than 0.5 /xm. The force measurements were performed with a fluid cell from Digital Instruments using freshly prepared solutions. Prior to the injection of the test solutions, the force was measured in air and a typical longrange attractive force profile was obtained. After the injection of the solution, the system was allowed to equilibrate for 15 min prior to the force run. A few force runs were performed under each test condition and only the representative force curves were analyzed using the established algorithm [16]. The measured forces (F) were
normalized by the local radius of the silica sphere (R) as F/R for comparison with the theory.
