Student Project Abstracts 2005 - Pluto - University of Washington

SYNTHESIS AND ANALYSIS OF THIOL-STABILIZED NANOPARTICLES(a)(b)Figure 2. Absorption spectra of silver nanoparticles in polystyrene thin films. The particles were coated with octanethiol to dodecanethiol ratios of (a) 1:1 and (b) 3:1Nanocomposite FilmsThe silver nanoparticles were dissolved in a polystyrenematrix and made into thin films to study their optical properties.The first method used to make these films was spin coating. Thenanoparticles and polystyrene were first dissolved in a solventsuch as toluene and placed in a small vial. A small amount ofsolution was then drawn from the vial with a syringe. A glasssubstrate was placed onto the spin coater and the solution wasfiltered and dispensed onto the substrate evenly. The substratewas allowed to spin for two minutes at 1000 rpm. UV-vis absorptionspectra were measured for these films with varying ligandratios and nanoparticle concentrations. Films made in thismanner, however, were too thin to be used for x-ray diffractionstudies, so a different method, (solvent-evaporation method), wasemployed. The glass substrates also had to be modified with anadhesion promoter to keep the polymer from peeling off of theglass slides.Three drops of the adhesion promoter solution were put ontothe slide and the slide was then rotated at 3000 rpm for 3 secondson the spin coater. The slide was then heated at 90°C on ahot plate for 30 seconds. This process was repeated 3 times. Initially,to make the nanocomposite films, a microscope slide wascovered with the nanoparticle/polymer solution and placed in anevaporation chamber overnight to allow the solvent to slowlyevaporate. The films obtained were thick enough for x-ray diffractionmeasurements, but the particles were not very well dispersedthroughout the film. This was likely due to the particlesaggregating overnight as the solvent evaporated.To try and prevent the aggregation of particles the solutionswere filtered in the same way but the films were prepared at ahigher temperature. The temperature had to be lower than theboiling point of the solvent to keep the film from bubbling, soa solvent with a high boiling point was used (dichlorobenzene).The modified slides were placed on a hot plate and first heatedto 120°C. The nanocomposite solution was then filtered onto theslides and allowed to sit for 1 hour.RESULTSAbsorption spectra were obtained for the nanocompositefilms made by spin coating (Fig. 2). The nanoparticles were synthesizedwith octanethiol to dodecanethiol ligand ratios of 1:1 and3:1. The concentration of nanoparticles for each successive filmin each graph was decreased by one-half. The absorption spectrafor the 1:1 films exhibit a shoulder at about 400 nm, which as ofnow cannot be fully explained. The absorption peaks of the 1:1films are narrower than those of the 3:1 films, which may correlatewith a change in the shape and distribution of silver nanoparticleswithin the polymer matrix. A blue shift in the position of theplasmon resonance band is observed when the concentration ofnanoparticles in the film decreases.58 CMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005