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Applications of Fluorescence Spectroscopy to the Study of Polymer-Surfactant Interactions
Published in E. D. Goddard, K. P. Ananthapadmanabhan, Interactions of Surfactants with Polymers and Proteins, 2018
For a chromophore to absorb light a component of its transition moment must be parallel to the electric vector of the incident light. As a consequence, irradiating a sample of randomly oriented molecules with plane-polarized light results in an optical selection of which molecules are excited. If the motion of these molecules is slow compared to the timescale of fluorescence, the emitted light will also be polarized, and its degree of polarization will be related to the extent of motion of the molecule. In this way fluorescence depolarization can be used to determine the apparent microviscosity of a medium containing a suitable fluorescent probe. One can measure the time profile of polarization decay in a time-resolved experiment or one can measure the steady-state polarization with a fluorescence spectrometer equipped with polarizers.
Solute dynamics in a block copolymer: effect of additives and temperature
Published in Molecular Physics, 2022
Sanyukta Bhattacharjee, Souvik Pandit, Debabrata Seth
The microviscosity was calculated using the rotational diffusion coefficient (Dr) obtained from the Stokes–Einstein equation and correlation time (r) for a spherical micelle [33]. Using the Edwards method [34], the radius of C-6 molecule was found to be 4.165 Å. In the equation used, T stands for temperature in Kelvin scale, η stands for microviscosity, r stands for radius of probe molecule. Though the above equations are applicable only when anisotropy decays are single exponential in nature however, we have extended our calculations even to biexponential anisotropic decays for comparison purposes in few systems. The biexponential decays have been asterisk marked in (Tables 3–5).
Fast field cycling NMR relaxometry studies of molten and cooled cocoa butter
Published in Molecular Physics, 2018
Marjorie Ladd-Parada, Megan J. Povey, Josélio Vieira, Michael E. Ries
Comparing the different treatments, it is possible to observe that there was no hysteresis between the cooling and heating protocols (Figure 2(A,B)), nor between the two maximum temperature treatments, 50°C or 110°C (Figure 3). This lack of hysteresis indicates that whilst changes in microviscosity of TAG systems have been reported by previous authors [50], they are not observable by bulk self-diffusion measurements, suggesting they only occur in localised areas, probably near the ends of the FA side chains or in the areas surrounding newly formed nuclei. It is noted, however, that there is a difference in the diffusion coefficients measured at 70°C (Figure 2(B)). It is tempting to associate this behaviour with a phase transition as it coincides with the melting point of tristearin [51-53], which is one of the minor components in CB. Regardless, given that at lower temperatures the diffusion coefficients do not deviate from those of the heating protocol, it is likely that this point is only an outlier.