Characterization of Ag Nanoparticle Films at the Liquid-Liquid Interface.
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Nanoparticles can be packed together and organized into a well-ordered array, known as a superlattice. One way of forming this superlattice is at the aqueous-organic interface, developed in the laboratory of Professor Eileen Spain. The film is defined by a vibrant blue opalescent color, and is dependent on the presence of the nanoparticles. In addition, the film has the ability to coat the glass walls of the reaction vial, whereupon it loses the blue tinge. UV-Visual spectra of the particles in chloroform, the film on the glass, and the particle film re-dissolved in ethanol were obtained. It has been found that the wicked up film results in a red-shifted, broadened absorbance peak. This is a result of the collective oscillation of the closely packed nanoparticles, characteristic of a superlattice. Also, the nanoparticles in the wicked up film remain stable upon dissolution in ethanol. Additional experiments were performed in order to determine the threshold value of MUA needed to form the blue opalescent film. Further, the water and ethanol proportions in the aqueous mixture were varied, and it was noted that the films at the liquid-liquid interface are more stable (and less wicking occurs) when the ratio between ethanol and water is decreased from 50/50 to 60/40. Finally, we noticed that the film formed at the liquid-liquid interface can be ?silvery? in appearance, indicative of possible metallic behavior. Future reflectance measurements will be conducted to confirm whether a metallic film has formed at the liquid-liquid interface.