NONLINEAR OPTICAL TECHNIQUES TO STUDY POLYMER ADSORPTION
| Autor: | Rao, Ashwin B. |
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| Jazyk: | angličtina |
| Rok vydání: | 2006 |
| Předmět: | |
| Druh dokumentu: | Text |
| Popis: | The adsorption of Fluorescein Isothiocyanate (FITC) labeled polystyrene at the water-toluene interface was studied by two-photon fluorescence spectroscopy. This system was used to develop a model to predict the concentration of polymer molecules adsorbed at the interface. For FITC labeled polystyrene of Mw: 50.5 Kg/mole, the concentration at the interface was found to be 1 mg/m2. This corresponds to an area of 82 nm2 per molecule, which indicates that the adsorbed molecules adopt a brush like conformation at the interface. The results also show the importance of accounting for fluorescence resonance energy transfer effects (FRET) in determining the concentration of the adsorbed polymers. Neglecting FRET at the interface results in an underestimation of the surface excess by a factor of 2. We have also studied the orientation of the chemical groups of poly (methyl methacrylate) (PMMA) adsorbed at the sapphire-CCl4 interface using a technique known as infrared-visible sum frequency generation spectroscopy. The ester methyl groups of PMMA are strongly oriented at the sapphire interface while the methylene and alpha methyl groups of the polymer chain appear to be disordered. The orientation of the ester methyl groups at the interface of a PMMA film and sapphire is very similar to the orientation of the ester methyl groups of an isolated PMMA chain adsorbed on sapphire. The structure of the adsorbed polymer chains is not affected by the solvent quality nor is it affected by the degree of polymerization of the chain. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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