Data analysis time-domain spectroscopy

The use of nonlinear least-squares analysis is ubiquitous in the analySK of fluorescence data, pairicululy time-domain and fiequency-domain data. A usefiil introduction to the principles of least-squares analysis is found in the compact but informative book by Bevington (1969). The applications of these concepts to diverse types of fluorescence data can be found in edited volumes (Brand and Johnson, 1992 Johnson and Brand, 1994). For more basic information about statistics and spectroscopy, one can examine several introductoiy texts (Ihylor, 1982 Mark and Workman, 1991). 

The applicability of the ESE envelope modulation technique has been extended by two recent publications115,1161. Merks and de Beer1151 introduced a two-dimensional Fourier transform technique which is able to circumvent blind spots in the one-dimensional Fourier transformed display of ESE envelope modulation spectra, whereas van Ormondt and Nederveen1161 could enhance the resolution of ESE spectroscopy by applying the maximum entropy method for the spectral analysis of the time domain data. 

A general discussion of the use of least-squares fitting in fluorescence measurements may be found in (28). The global analysis of fluorescence data is discussed in (29). Commercially available time-resolved fluorimeters are typically sold with data analysis software included. Available stand-alone packages include the Globals Unlimited suite, which is capable of analysing both time- and frequency-domain data, stopped-flow kinetics, etc. The Center for Fluorescence Spectroscopy at the University of Maryland (USA) also offers software for frequency- and time-domain fluorescence lifetime analysis. 

Other processing techniques for analysis of F.t.-i.r. data have been developed in order to obtain the maximum of information from the spectra. The advances made in time-resolved techniques, which sample only a portion of the interferogram, permit obtaining of spectra in the microsecond domain this will lead to additional applications of F.t.-i.r. spectroscopy such as the study of dynamic and kinetic processes. 

These authors noted that the intermediate power law (i.e., t l+y, with a small positive 7) of the OKE data was formally equivalent to the excess wing in the frequency-dependent susceptibility, the latter discussed in the dielectric literature since 1951. Brodin and Rossler argued that the intermediate power law observed in the OKE data was in essence a manifestation of the excess wing of the corresponding frequency-domain data, known long since from broadband dielectric spectroscopy and anticipated from DLS studies of supercooled liquids [83]. More recently, these authors showed that the excess wing was an equally common feature of the DLS data and discussed the merits of the Mode coupling theory analysis of the time and frequency-domain data [84]. 

Recent developments have been in the area of microthermal analysis using thermal conductivity with thermal diffiisivity signals or AFM to visualize specific areas or domains in the material and perform localized thermal analysis studies (183,184). Relaxational behavior over time and temperature is related to changes in free volume of the material. Positron annihilation lifetime spectroscopy (PALS) measurements of positron lifetimes and intensities are used to estimate both hole sizes and free volume within primarily amorphous phases of polymers. These data are used in measurement of thermal transitions (185,186) structural relaxation including molecular motions (187-189), and effects of additives (190), molecular weight variation (191), and degree of crystallinity (192). It has been used in combination with DSC to analyze the range of miscibility of polymethyl methacrylate poly(ethylene oxide) blends (193). 

Dielectric spectroscopy also allows monitoring the structural relaxation time and, eventually, its slowdown as expected in the case of higher fractions of MROs. Furthermore, investigation of the form of the relaxation peaks in the frequency domain permitted us to characterize the dynamic heterogeneity of our films. For this purpose, a quantitative analysis was achieved via fits of the experimental data to the Havrialiak-Negami equation... 

---