Determining the colloidal forces between bitumen droplets in water using the hydrodynamic force balance technique

A novel technique using a "hydrodynamic force balance" was introduced to de termine the maximum value of attractive forces between two micrometer-sized bitumen droplets in a doublet suspended in water. The technique is based o n breaking up a doublet in a gradually increasing wall shear flow and calcu lating the colloidal force between the two droplets from the breakup shear rate. The measurable force ranges from 10(-13) to 10(-11) N. The upper limi t can be further raised after some modifications to the instrument. The val idity of the method has been verified by comparing the determined Hamaker c onstant of bitumen water-bitumen with both the experimental data obtained f rom another force-measurement technique and the literature value. The methe d is applicable to both emulsion and suspension systems although only a bit umen-in-water emulsion was investigated in this study. A bitumen droplet su rface contains isolated "bumps" of 50-100 nm in horizontal diameter accordi ng to previous study. A disk-sphere model assuming a single disk-shaped pro trusion attached to the bitumen droplet was used to interpret the force dat a. The calculation yielded the thickness values of the protrusions mostly i n the range of 0-20 nm, which are consistent with the previous findings.