Dynamic light scattering segmental

There continues to be extensive interest in latexes and micellar systems. The structure of acrylic latex particles has been investigated by non-radiative energy transfer by labelling the co-monomers with fluorescent acceptor-donor systems. Phase separations could also be measured in this way. Excimer fluorescence has been used to measure the critical micelle temperature in diblock copolymers of polystyrene with ethylene-propylene and the results agree well with dynamic light scattering measurements. Fluorescence anisotropy has been used to measure adsorption isotherms of labelled polymers to silica as well as segmental relaxation processes in solutions of acrylic polymers. In the latter case unusual interactions were indicated between the polymers and chlorinated hydrocarbon solvents. Fluorescence analysis of hydrophobically modifled cellulose have shown the operation of slow dynamic processes while fluorescence... 

FIGURE 6.7 Atactic polypropylene segmental relaxation times (solid symbols) from mechanical spectroscopy, dynamic light scattering, dielectric relaxation, and NMR, along with the global time-temperature shift factors (open symbols) from dynamic mechanical spectroscopy, creep compliance, and viscosity. Vertical shifts were applied to superpose the data (Roland et al., 2001). 

A pH dependent self-assembly behavior was also observed for PNHOS-PEO diblock copolymers [12]. The presence of basic and acidic groups on the same segment of the PNHOS block allows for variation of the solubility and the internal structure of the aggregates formed at different pH values, as it was confirmed by dynamic light scattering and fluorescence spectroscopy. 

Fig. 19. Temperature dependence of the shift factors of the viscosity (T), terminal dispersion ( ), and softening dispersion (0) of app from Ref. 73. The temperature dependence of the local segmental relaxation time determined by dynamic light scattering ( ) (30) and by dynamic mechanical relaxation (o) (74). The two solid lines are separate fits to the terminal shift factor and local segmental relaxation by the Vogel-Fulcher-Tammann-Hesse equation. The uppermost dashed line is the global relaxation time tr, deduced from nmr relaxation data (75). The dashed curve in the middle is tr after a vertical shift indicated by the arrow to line up with the shift factor of viscosity (73). The lowest dashed curve is the local segmental relaxation time tgeg deduced from nmr relaxation data (75).

In dynamic light-scattering, the scattered intensity is mostly due to concentration fluctuations. Tvo different types of motion in polymer solutions mainly contribute to the fluctuations (a) the translational motion of the center of mass of the individual molecules, and (b) the internal modes of motion of segments with respect to their centers of mass (58). 

Finally, we can mention that various factors related to the adsorption of polymers can be measured, e.g. the adsorbed amount via ellipsometry and reflectometry, the layer thickness (Rg) via dynamic light scattering, the heat of adsorption via calorimetry, the fraction of polymer in actual contact with surface via spectroscopy (NMR, IR) and segment density distribution via SANS (small-angle neutron scattering). 

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