An ammonium free radical initiator was ion exchanged onto the surface of clay layers. Polystyrene (PS) and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) mixed polymer brushes on the surface of clay layers were prepared by in situ free radical polymerization. PS colloid particles armored by clay layers with mixed polymer brushes were prepared by Pickering suspension polymerization. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the structure and morphology of the colloid particles. Clay layers on the surface of PS colloid particles can be observed. Because of the cationic nature of the PDMAENU brushes the colloid particles have positive zeta potentials at low pH values. X-ray photoelectron spectroscopy (XPS) was used to analyze the surface of the colloid particles. N-1s, binding energy of PDMAEMA chains on the surface of clay layers was detected by XPS. The two peaks of the N-1s binding energy indicate two different nitrogen environments on the surface of clay layers. The peak with a lower binding energy is characteristic of neutral nitrogen on PDMAEMA chains, and the peak with a higher binding energy is attributed to protonated nitrogen on PDMAENIA chains. (c) 2007 Wiley Periodicals, Inc.