Topology and porosity modulation of polyurea films using interfacial polymerization

Abstract

Polyurea (PU) films are interesting owing to the high mechanical properties and wide range of applications. Here we report an interfacial synthesis of a PU thin film at the liquid–liquid interface using the reaction between diisocyanate and polyamines. Three amines – polyethylenimine (PEI), diethylenetriamine (DETA) and tris(2-aminoethyl)amine (TREN) were dissolved in the aqueous phase separately and allowed to react with an organic solution of hexamethylene diisocyanate (HMDI) at the liquid–liquid interface. The structure and morphologies of the films were established using spectroscopic and microscopic techniques. Smooth PU films were obtained from the reaction of HMDI with PEI, whereas films with holes and tubules were obtained from small molecular amines such as DETA and TREN. Such observations are explained based on the differences in solubility, reactivity of the reagents and molecular size dependant diffusion across the film. The effect of the changes in concentration of reactants and time of reaction on film thickness and transport of organic dye molecules through the film were investigated. PEI gave a smooth defect-free film of PU, whereas small molecular amines upon reaction with HMDI gave films with significant number of defects. To demonstrate the accessibility of functional groups on the film, adsorption of fluorescent dyes on the film surface was investigated. From the UV-Vis spectroscopic measurements, it is clear that acidic molecules adsorb on the surface of the films and the corresponding esters are not extracted efficiently by the film. In summary, the synthesis and characterization of PU films from multiple amines, and the transport of small molecules and adsorption of dyes on the surface of the films were established.