The Research And Fabrication Of Compound Materials Including Polymer And Nanoparticles

This thesis mainly includes two parts, the first one is"Self-assembly ofλ-DNA Networks /Ag Nanoparticles: Hybrid Architecture and Active-SERS substrate", and the second one is"Fabricating nanocomposite materials by deoxidizing silver ions in PEI/PSS multilayer films".In the first part, highly rough and stable surface enhanced Raman scattering (SERS)-active substrates had been fabricated by a facile layer-by-layer technique. Uniqueλ-DNA networks and CTAB capped silver nanoparticles (AgNP) were alternatively self-assembled on the charged mica surface until desired number of bilayers were reached. The as-prepared hybrid architectures were characterized by UV-vis spectroscopy, tapping mode atomic force microscopy (AFM) and confocal Raman microscopy, respectively. Linear increases of the maximum absorbance of DNA band with the number of bilayers present a common LBL assembly feature. The red-shift of surface plasmon of silver nanoparticles within the hybrid films was mainly due to the aggregation effect. With the increasing of number of bilayers, the surface coverage of nanoparticles on the substrate became larger, as well as the rising of total amount of nanoparticles and the surface roughness of hybrid films. These rough metallic hybrid architectures could be utilized as SERS-active substrates. A significant enhanced Raman scattering effect of the adsorbed analytes, e.g. methylene blue (MB), on these hybrid films was easily exploited by the confocal Raman microscopy. The enhancement factor depended on the surface coverage of nanoparticles and number of bilayers ofλ-DNA/AgNP. In the second part, Alternating adsorption of polyethyleneimine (PEI) and poly (sodium styrenesulfonate) (PSS) using the layer-by-layer method results in the formation of multilayer polyelectrolyte films. The films were subsequently utilized as nanoreactors for fabricating metal nanoparticles (NPs). Since the primary, secondary, and tertiary amine groups of PEI allow formation of complexes with a wide variety of transition metal cations, they were used to bind Ag+. Reduction of the silver ions incorporated in the films by exposure to sodium borohydride (NaBH4) then yields composite films containing metal NPs. The presence of silver NPs within the films was confirmed by UV-Visible spectroscopy (UV-Vis) and X-ray photoelectron spectroscopy (XPS). Then the state of silver NPs within the polyelectrolyte matrixes was further investigated by means of AFM. The images of AFM after the incorporation of silver NPs suggest that silver nanopartiles are well dispersed when few bilayers are added. However, when the number is large (eg.10 bilayers), there will be aggregation, which also has some influence on the structure of PEI/PSS multilayer films. The method we used in this article demonstrated that the complex of PEI with Ag+ could be used to incorporate metallic cations into multilayer films and cations can be in turn conversed into NPs and constitutes a new way to fabricate organic/inorganic nanocomposite materials.