(549g) Modeling of Interfacial Polymerization to Nanocapsule Formation

The nano-encapsulation technique of active principle (solid or liquid) by polymer coating is largely described in the literature. This work provides an understanding for the effective control of the nanocapsules membrane thickness. Polyamides based nanocapsules are prepared by the interfacial polymerization combined with spontaneous emulsification. An organic phase composed of a water miscible solvent , a lipophilic monomer ( A), an oil, a lipophilic surfactant and an active principle , injected in an aqueous phase containing hydrophilic monomer triamine (B) and the hydrophilic emulsifying agent. The water miscible solvent diffuses to the aqueous phase, the oil precipitates as droplets, and the two monomers react at the interface, forming insoluble polymeric membrane around the nano emulsion leading to nanocapsules (200 nm of diameter). The membrane thickness results also on the swelling due to water sorption. No existing model represents all the phenomena occurring such as the swelling. The modelling presented here, is done on a population of identical particles of 100 nm diameter. The membrane radius around the nanocapsule expands by swelling of polymer and by the reaction of polycondensation. The diffusion in the polymer is described by Fick law. With these assumptions, the mass balances in spherical geometry are made in the different volumes .The simulation is made and the final thickness of the capsule is found to 4.4 nm. This result is in the same order of magnitude than the measurement (2 nm) with the transmission electron microscopy (TEM) Topcon® EM002B, 200kV and considering the precision of the measurement, it appears to be satisfying. The membrane is porous (0.67). The diffusion coefficient of B in the membrane is in the same order than the one computed by the correlation of the molecular liquid-liquid diffusion: the membrane does not offer resistance to the active principle but protects the latter.