The influence of the disk diameter of nanometer thick anisotropic layered silicates on the phase-separated morphology of a near-critical polystyrene (PS)-poly(vinyl methyl ether) (PVME) blend was examined using atomic force microscopy. Films with comparable amounts of thermodynamically equivalent nanoparticles varying only in lateral disk diameters were examined using a temperature gradient method and showed dramatic differences in late-stage morphology. The blends with small disk diameter (30 nm and 0.5 mum) nanoparticles exhibit a pinning of domain sizes and demonstrate an increase in the number of domains with a higher fraction of near circular structures. On the other hand, for layered silicates with large disk diameters (10 mum), the nanoparticles do not affect the morphology of the phase-separated structure and only accelerate the phase separation kinetics. The extent of domain pinning increases with increasing silicate content and results in smaller domains at higher concentrations of silicate.