SURFACE ATTACHMENT AND STABILITY OF CROSS-LINKED POLY(ETHYLENIMINE) EPOXY NETWORKS ON GOLD

The formation of thin films of 3-glycidoxypropyltrimethoxysilane (GPS) on gold was studied by reflection-absorption infrared spectroscopy (RAIR) and optical ellipsometry. Mass changes on the surface were measured with the quartz crystal microbalance (QCM). Thin films of poly(ethylenimine) (PEI) were formed on these modified gold surfaces and crosslinked with the diepoxy compound EPON (bisphenol A/epichlorohydrin epoxy resin). The resulting films are reactive toward HSiClMe2. The expected substitution of chloride at the silicon center is observed, showing that amino and/or oxo ligands are available on the surface. The stability of the PEI/EPON films in water at different pH and temperatures was studied by electrochemical methods and compared to that of monolayers of octadecylmercaptan (ODM) and octadecyltrichlorosilane (OTS). ODM on gold is quite stable at neutral and basic pH in aqueous solution up to 100-degrees-C. Films of PEI, covalently bonded to the GPS layer and cross-linked with EPON, are extremely durable. The drastically reduced Faradaic response of these films is consistent with a continuous coating. The films withstand temperatures in the range of 25-100-degrees-C at pH 6 and 9 for several hours. These films show promise for applications as barrier coatings and thermostable reactive interfaces.