Evidence for hydrophobic attraction between latex particles in aqueous systems as investigated by turbidimetry

We report the evidence for attractive interaction of latex particles which are covered by poly(ethylene oxide) chains. These particles are suspended i n aqueous solutions of ammonium sulfate. The interaction is probed by measu rements of the turbidity of the suspensions up to 70 g/l. Turbidity is inse nsitive to multiple scattering and allows the static structure factor, S(q) [q = (4 pin(0)/lambda (0))sin(theta /2), where theta is the scattering ang le, no is the refractive index of the medium and lambda (0) is the waveleng th in vacuo], to be determined at small q values. The analysis of S(q) at s mall q values yields information about possible attraction of the particles . The analysis of the turbidity data furthermore shows that no aggregation took place in these systems. A weak but long-range attractive interaction w as found at ammonium sulfate concentrations of 0.01 and 0.1 M. The relation of this attractive force to hydrophobic forces is discussed.