Photon correlation spectroscop

In this connection the surprising thermal stability of AOT micelles in nonpolar solvents has been demonstrated again with the help of photon correlation spectroscopic experiments227 in the AOT/isooctane system between —85 and +95 °C. This was explained by the formation of a hydrogen bond network where it was assumed... 

Tri-styrene has been mentioned before in this section. It has a much narrower a-relaxation dispersion [242] compared with that of higher-molecular-weight polystyrene. Tristyrene has no resolved JG relaxation because n is small and hence the separation distance, log10v/c — log10va, is small. On the other hand, polystyrene has a resolved JG relaxation [ 194,347] because it has a broad a-relaxation dispersion and n = 0.64 from photon correlation spectroscopic measurement [210]. 

However, in order for this explanation to be consistent with the observed monotonic increases of the products A and Dttc as the temperature is lowered toward A the breadth of the relaxation time distribution has to increase (or the Kohlrausch exponent, l-n, has to decrease) correspondingly. However, for two glassformers, ortho-terphenyl (OTP) and tni naphthylbenzene (TNB) which show the breakdown of the SE and DSE relations, Richert and coworkerss recently reported that their dielectric spectra are characterized by a temperature independent width (e.g. l-rid is constant and is equal to 0.50) from 345-417 K in the case of TNB. The Tg of TNB is 342 K. Photon correlation spectroscopic and NMR measurements all indicate a temperature-independent distribution of relaxation times. Thus, the data of TNB and OTP contradicts the explanation based on spatial heterogeneities. On the other hand, an alternative explanation based on intermolecular coupling (originating from many-molecule relaxation) continues to hold. ... 

Most of the available information stems from thermodynamical investigations. Comparatively little work was directed towards structural details. Only more recently a systematic photon correlation spectroscopic study has been performed (15) on ternary W/O- microemulsions, i.e. H20/A0T/isooctane, which revealed gener-alizable results regarding ternary W/O- microemulsions formed by... 

Dielectric relaxation and photon correlation spectroscopic measurements (to be discussed later) have found that the stretched exponential time correlation fimction of the Q -relaxation of amorphous polymers, exp[ — it/Taf"], has Pa that varies from polymer to polymer. For example, PS and PIB have Pa equal to 0.36 and 0.55 respectively. It was recognized that this difference in the stretched exponent Pa of PIB and PS is the origin of their contrasting viscoelastic properties 12,IQ, 121,122). 

Rizos A, Fytas G, Lodge TP, Ngai KL (1991) Solvent rotational mobility in polystyrene Aroclor and polybutadiene Aroclor solutions. 2. A photon-correlation spectroscopic study. J Chem Phys 95(4) 2980-2987. doi 10.1063/1.461800... 

Wu, C., Unterforsthuber, K., Lilge, D., Luddecke, E., Horn, D., Determination of Particle Size Distribution by the Analysis of Intensity-constrained Multi-angle Photon Correlation Spectroscopic Data, Part. Part. Syst Charact, 1994, 11, 145-149. 

Van der Meeren, P., Bogaert, H., Vanderdeelen, J., Baert, L., Relevance of Light Scattering Theory in Photon Correlation Spectroscopic Experiments, Part. Part. Syst Charact, 1992, 9, 138-143. 

Results from Other Spectroscopic Techniques and Photon Correlation Spectroscopy... 

Results from other spectroscopic techniques and photon correlation spectroscopy have been compared for aPP in [126] (see Fig. 4.11). A scaling of the dynamic structure factor at could not be achieved on the basis of the dynamic data reported in [140]. The other temperature dependencies obtained seem to be compatible with the neutron data. Finally, the temperature dependence deduced by Tormala for PIB from the compilation of different spectroscopic data does not agree with the result of the microscopic observation of the structural relaxation (see Fig. 4.9 [125]). 

The study of optical lattices has been extended from ID to 2D and 3D using the phase-insensitive configurations mentioned above, and also by stabilization of the relative phases of the beams [30]. The spectra of such lattices has been studied by both absorption and emission techniques [24, 31, 32, 33, 34], as well as by photon correlation techniques [35, 36]. There have also been studies of lattices tuned far from resonance, using non-spectroscopic methods [37, 38]. ... 

Obviously, all of the proposed relationships discussed so far are linear. However, there are also very clear examples where a strong linear relationship was not so obvious, at least not for the total range of w values of the microemulsions studied by different workers. Zulauf and Eicke [76] clearly showed from photon correlation spectroscopy curvilinear relationships between w (up to 50) and the Stokes radius of the water pool in the system AOT/isooctane /H2O (Fig. 3.11). The curves, however, could be divided into linear parts with different slopes. Similarly, acoustic spectroscopic studies of the system A0T/heptane/H20 by Wines et al. [ 152] exhibited a non-linear relationship between the mean diameter of water droplets (from about 8 nm to 17 nm) and the w value (10 to 60) there was no appreciable change from w = 10 to w = 20, but this part of the curve could be taken as linear with a very gentle slope (Fig. 3.12). In the system AOT/isooctane/ H2O, Chen et al. [153] found a linear relationship only up to w = 10. 

Photon spectroscopy associates two numbers with the pair of states involved in a transition, the energy-level difference and the transition rate. The correlated emission directions of photons in successive transitions are determined trivially by the dipole selection rule. In most cases it is impossible to solve the many-body problem accurately enough to reproduce spectroscopic data within experimental error and we are left wondering how good our theoretical methods really are. 

There are numerous spectroscopic studies of the chromophores bound to the chemically modified silica gel(2-4) but dynamic studies such as fluorescence lifetime measurements are rather limited. In their recent work, Lochmuller and Hunnicutt (5) have employed the time-correlated single photon counting technique and analyzed the non-exponential decays in detail to disclose the complex features of the interfaces through (10-(3-pyrenyl)decyl)dimethylmonochlorosilane chemically bonded to silica as a probe. Unfortunately, however, their method, though sophisticated enough to monitor heterogeneous fluorescence decays, cannot distinguish one microparticle from the other and hence unavoidably follows overall decays. 

Spectroscopic techniques based on the optical microscope are being used with increasing success in photophysics. Microscopic fluorescence decay measurements have been made on both thin liquid films and droplets of concentrated dye solutions.Illustrative data are given for rhodamine B in 20 pm films. A luminescence lifetime microscope spectrometer based on time-correlated single photon counting with an avalanche diode detector has measured... 

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