High PVC film‐forming composite latex particles via miniemulsification, part 2: Efficiency of encapsulation

The application of a density gradient column (DGC) method using sodium polytungstate (SPT) solutions as the medium was investigated for determining the encapsulation efficiency of 11–30% pigment volume concentration (PVC)) latex particles prepared by the miniemulsification process. The encapsulation efficiencies for 11, 20, and 30% PVCs were found to be 100% of the TiO 2 encapsulated inside 86.3, 98, and 98.9% of the styrene/ n ‐butyl acrylate copolymer, respectively. The copolymer not participating in the encapsulation (free copolymer) was found in the 1.04 g/mL density layer of the DGC. Particle size analysis by DLS (dynamic light scattering) showed that the encapsulated particle size increased with increasing density. Thus, the number of TiO 2 particles (primary particles) inside each encapsulated particle increased to accommodate both the increased size and density. The results obtained by DLS for each DGC layer of the 30% PVC system were confirmed qualitatively by TEM in terms of the increasing encapsulated particle size and broadening of the size distribution as the density increased in the DGC. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4517–4525, 2006