Retarded van der Waals Forces between Triblock-Coated Latex Spheres

Retarded van der Waals forces between colloidal particles play a major role in colloid and surface science, but no direct measurement of these forces has been reported. A new experimental technique has been developed to accurately determine these forces between two 4.7 μm latex spheres coated by triblock copolymers. The retardation wavelength has been found to be 110 ± 10 nm and the Hamaker constant (1.0 ± 0.1) × 10 - 20 J. Both of them agree well with theoretical predictions. In addition, the experiments allow the measurement of the layer thickness of adsorbed triblock copolymers. The results are consistent with the data from field-flow fractionation and photon correlation spectroscopy.