Light scattering studies on core-shell systems: determination of size parameters of sterically stabilized poly(methylmethacrylate) dispersions

Poly(methylmethacrylate) dispersions with a weight fraction of the stabiliz ing diblock copolymer polystyrene-block-poly(ethylene-co-propylene) x(s) = 0.035-0.9 and a micellar solution of the diblock copolymer were investigate d by static and dynamic light scattering. For high xs, the R-g/R-h ratio is significantly lower than the value of 0.775 for hard spheres, because of t he core-shell structure and different refractive index increments dn/dc of the polymer components. The core radius R-core decreases with increasing st abilizer content, corresponding to a wide range of molar masses. The hydrod ynamic shell thickness delta varies only slightly in accordance with previo us model calculations whereas the average segment concentration of the stab ilizer chains (C-Shell) is practically constant. The number of stabilizing chains per unit surface of the particle core sigma(s) increases with the sh ell-to-core mass ratio x(shell)/x(core). During polymerization one dispersi on particle grows from one micelle at x(shell)/x(core) greater than or equa l to 0.25 while at lower x(shell)/x(core) a smaller number of particles wit h a higher number of block copolymer chains are formed. (C) 2000 Elsevier S cience Ltd. All rights reserved.