Toward an approach for determining the Hamaker constant of soft materials using dynamic light scattering

The accurate determination of Hamaker constant of humus is the basis for understanding the colloidal behavior of humus in environment. However, the determination of the Hamaker constant of humus is still a challenge because of its low value in Hamaker constant. In this study, a method for determining the Hamaker constant of humus with dynamic light scattering (DLS) technique has been established. Firstly, the Hamaker constants of the mixture colloids of “humic acid (HA) + montmorillonite (Mont, with known high Hamaker constant)” with different HA/Mont ratios were determined by DLS technique. Secondly, the mathematic relationship of the Hamaker constant (A) of the mixture colloid and HA content (y with percentage) was established, and it was A = 13.32 × 10−20 y−0.507 J. From which, finally, the Hamaker constant of HA (when y = 100) was obtained and it was 1.29 × 10−20 J. The validity of the obtained Hamaker constant of HA was confirmed by the comparison of the calculated CCC by adopting the obtained Hamaker constant of HA and the experimentally determined CCC by DLS. The established method in this study can be applied to the Hamaker constant determination of other nano-sized organic materials by DLS.