The Decomposition Process of Melamine Formaldehyde Cores: The Key Step in the Fabrication of Ultrathin Polyelectrolyte Multilayer Capsules

Abstract

Melamine formaldehyde (MF) colloidal cores were coated with polyelectrolyte multilayers. The core decomposition process at low pH was followed by confocal laser scanning microscopy (CLSM). Transient capsule swelling as a result of the osmotic pressure difference created by the decomposition of the MF resin was observed. The rate of core dissolving and the permeation of decomposition products of the MF core through the capsule walls are discussed in relation to the extent of swelling and capsule wall rupture. The core decomposition products had a diffusion coefficient of 71 μm2/s, which corresponds to a hydrodynamic diameter of ≈ 4 nm. Simultaneously with the degradation of MF polymers the hydrolysis at the melamine groups to ammeline groups occurred as was shown by infrared spectroscopy. The size and chemical composition of the reaction products did not depend on the pH. The degradation rate increased with decreasing pH.