Methods of Structure Analysis

The idea by Rey to use ER during the main drying for control of the process has not been introduced largely, because as the measurement is not done in a solid block, the product becomes increasingly porous with unknown configurations. The ER measurement of physiological NaCl solution (Fig. 1.24) can be used to check the system. The ER measurement 

Platinum electrodes 2, temperature sensor in the heat transfer medium 3, resistance thermometer 4, product sample 5, heat transfer medium 6, resistance heating. 

DTA (Fig. 1.25) measures the different course of temperature between the sample and a probe, which changes its thermal behavior constantly but does not have a phase transition in the measured temperature range. Such an instrument is illustrated in Fig. 1.26. 

Using DTA and ER measurements of quickly (200 °C/min) frozen sucrose-NaCl solutions, Mac Kenzie presented the different events occurring during slow rewarming. Among others two sucrose-NaCl solutions were studied a 24 % sucrose solution with 6 % NaCl 

glass transition at approx. -78 °C 2, growth of crystals (exothermic) at approx. -52 °C 3, increase of cp, water is formed between the crystals 4, ice melts at approx. -7 °C. 

Crucible with sample 2, sample 3, thermocouple (reference crucible not enlarged) 4, gas inlet 5, ceramic support. 

The knowledge that successful freeze-drying depends largely on the structure of the frozen product has inspired the development of methods to analyze and understand these structures more quantitatively. Rey [1.24] has shown that in addition to the electrical resistance (ER) of a freezing substance, the thermodynamic behavior can also be used to study the freezing process and the frozen product. 

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Besides synthesis, current basic research on conducting polymers is concentrated on structural analysis. Structural parameters — e.g. regularity and homogeneity of chain structures, but also chain length — play an important role in our understanding of the properties of such materials. Research on electropolymerized polymers has concentrated on polypyrrole and polythiophene in particular and, more recently, on polyaniline as well, while of the chemically produced materials polyacetylene stih attracts greatest interest. Spectroscopic methods have proved particularly suitable for characterizing structural properties These comprise surface techniques such as XPS, AES or ATR, on the one hand, and the usual methods of structural analysis, such as NMR, ESR and X-ray diffraction techniques, on the other hand. 

Due to its greatly enhanced sensitivity in comparison to CW NMR, the PFT method has made 13C NMR into a routine method of structure analysis for all molecules having the natural 13C abundance of 1.1%. Additionally, phase-corrected PFT NMR spectra contain all spectral details without the lineskewing and ringing observed in CW spectra. Finally, short-lived molecules can be measured by PFT NMR, and sensitivity enhancement by accumulation of interferograms before Fourier transformation requires much less time than the accumulation of CW NMR spectra, due to the short time required for acquisition of FID signals. 

Methods of Structural Analysis. The most significant differences between structural models 1 and 2 are the prominent aromatic carbon content in model 1 and the aliphatic alicyclic ring content in model 2. Determinations of aromatic carbon content and ring content of fulvic acid might be useful for identifying sources and processes of degradation and fractionation. However, neither of these procedures is simple and straightforward. 

During the past 5-10 years a considerable increase in knowledge of the structure, chemistry, and processing of cellulose, as well as development of innovative cellulose products, has been observed. New frontiers involve sophisticated methods of structural analysis, environmentally safe cellulose-fiber technologies, as well as progressive work with bacterial nanocellulose, (bio)materials, and a broad spectrum of cellulose composites. 

Unlike experimental methods of structure analysis, there is no basis for estimating the error associated with a particular calculation. There is therefore an art, based on experience, in deciding the best level of approximation versus computing... 

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