Polymer dynamics studied by dynamic light scattering : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physics at Massey University

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Date
1998
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Massey University
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Abstract
Theoretical treatments of dynamic properties of polymer solutions are reviewed. Particular emphasis is placed on the discussion of diffusion in polymer solutions. The relationship between the slow diffusion coefficient found by Dynamic Light Scattering (DLS) and the Self Diffusion Coefficient is shown. An introduction to DLS theory is given. The experimental techniques involved in DLS measurements are discussed. Concentration dependencies of the DLS observed slow diffusion coefficient in ternary polymer solutions of polystyrene-poly vinyl methyl ether-solvent have been measured. Solvents used were toluene, carbon tetrachloride and tetrachloroethylene and the polymer molar masses were 110 000 gmol -1 for both polystyrene (PS) and poly vinyl methyl ether (PVME). Solvents were chosen to be very nearly isorefractive with PVME. Toluene is very nearly an equally good solvent for the polymer pair PS and PVME, while tetrachloroethylene is equally poor for both polymers. Carbon tetrachloride is an unequal quality solvent for this polymer pair. The results of these DLS measurements are reported. Four sets of experiments are described. The first is the effect on the relationship between D 1 (the slow mode diffusion coefficient found by DLS) and D s (the self diffusion coefficient) of different mass fractions in the polymer solution. It is found the mass fraction, x, has little effect on the observed diffusion coefficient. Secondly the effect of the polymer-polymer interaction parameter, x, on the relationship between D 1 and D s is investigated. It is found solutions formed with equal quality solvents have D 1 nearly equal to D s . But solutions formed with unequal quality solvents have D 1 considerably less than D s and that these solutions suffer phase separation at lower concentration. Thirdly the effect of polymer molar mass on the relationship between D 1 and D s is investigated. These are found to be in line with those expected from literature. Fourthly the considerable discrepancy between D 1 and D s which is manifest in 110 000 gmol -1 PS/ 110 000 gmol -1 PVME/ toluene solutions at polymer volume fractions greater than 0.4 is investigated. The diffusion coefficient found, D 1 , does not fit a unique concentration power law. Two unique regions are seen with concentration exponents of -11±4 and -14.9±0.7 for the low and high concentration regions respectively. This is found to agree with results found in literature.
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Appendix 1 and 2 – articles have been removed due to copyright. The articles are available in the print copy held in the library.
Keywords
Polymers -- Analysis, Light -- Scattering
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