THE EFFECT OF PARTICLE-SIZE ON THE LAYER THICKNESS OF A STABILIZING POLYMER ADSORBED ONTO 2 DIFFERENT CLASSES OF POLYMER LATEX, AS DETERMINED FROM RHEOLOGICAL EXPERIMENTS

The effect of the particle size on the adsorbed layer thickness of an ABA block copolymer has been studied using theological techniques. Several poly(methyl methacrylate) (PMMA) and polystyrene latices were prepared and stabilised with the minimum amount of copolymer, calculated from adsorption isotherms. The thickness of the adsorbed layer was then determined using two different theological techniques; firstly by comparing the high shear rate limiting viscosity to the Krieger-Dougherty equation, and secondly by measuring the elastic modulus of the dispersion. The results from the two methods were in reasonable agreement. For the same polymer the adsorbed layer thickness increased with the particle radius and was found to scale with the radius to a power of 0.80 for the PMMA latices and with 0.60 for the polystyrene latices. The results are in broad agreement with earlier light scattering studies. The particle size effect could not be explained fully by conventional geometric arguments, associated with the fact that the volume available to the polymer around a small particle for a given adsorbed layer is greater than that for a larger particle. As the adsorbed amount of copolymer on both latices was similar (about 1.6 mg m(-2)) the difference in the scaling power between the two sets of particles must be due to different adsorption characteristics, a consequence of the different surface properties of the latex particles.