Thin-film calorimetry

Many different methods have been used to monitor the kinetics of cationic ring-opening photopolymerizations. Among the most commonly used techniques are real-time infrared spearoscopy, differential scanning photocalori-metry, " thin-film calorimetry, and optical pyrometry. ... 

The study and control of a chemical process may be accomplished by measuring the concentrations of the reactants and the properties of the end-products. Another way is to measure certain quantities that characterize the conversion process, such as the quantity of heat output in a reaction vessel, the mass of a reactant sample, etc. Taking into consideration the special features of the chemical molding process (transition from liquid to solid and sometimes to an insoluble state), the calorimetric method has obvious advantages both for controlling the process variables and for obtaining quantitative data. Calorimetric measurements give a direct correlation between the transformation rates and heat release. This allows to monitor the reaction rate by observation of the heat release rate. For these purposes, both isothermal and non-isothermal calorimetry may be used. In the first case, the heat output is effectively removed, and isothermal conditions are maintained for the reaction. This method is especially successful when applied to a sample in the form of a thin film of the reactant. The temperature increase under these conditions does not exceed IK, and treatment of the experimental results obtained is simple the experimental data are compared with solutions of the differential kinetic equation. 

Differential calorimetry has been applied to the study of rapid photopolymerizations. This new technique holds great promise for basic and applied research on photopolymerization and other photochemical reactions. The method requires only a few milligrams of sample, can be used on network-forming systems, and can approximate actual conditions of thin film and coating technologies. 

In this chapter we investigate and discuss the thermal, optical, electrical properties of the oligothiophene derivatives by means of differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and UV-Vis spectroscopy. The thin films of these compounds produced by solution cast and vacuum deposition methods are characterised by AFM measurements in contact and non-contact mode, and by X-ray diffraction. Finally, an ultra-thin OFET is built, and the transistor characteristics are determined. 

A hybrid QCM/calorimetry device, Masscal, has been developed recently [199]. This technique combines the mass measurement change upon gas adsorption with the accompanying isothermal heat flow that allows a molar binding enthalpy to be determined. Various thin film chemical and biochemical systems have been studied, such as the hydration isotherms and associated hydration enthalpies determined for the immobihzed enzyme lysozyme [200]. 

Numerous oxidation tests are available to screen vegetable oil oxidative stability including thin film oxygen uptake test (TFOUT, ASTM D 4/42), rotating bomb oxidation test (RBOT, ASTM D 2272), panel coker test, and pressurized differential scanning calorimetry (Biswas et al., 2007 Erhan et al., 2006 Sharma et al., 2005,... 

Photoacoustic (PA) spectroscopy is a combination of optical spectroscopy and calorimetry [58]. It is a technique for studying those materials that are unsuitable for the conventional transmission or reflection methodologies. It can be used to measure thermal and elastic properties of materials, to study chemical reactions, to measure the thickness of layers and thin films, and to perform a variety of other non-spectroscopic investigations. This technique can be applied to different types of inorganic, organic and biological materials in the gas-, liquid-, or solid phase. Nowadays, PA spectroscopy is mainly employed for material characterization [59]. Compared with other spectroscopic techniques, PA spectroscopy provides a non-destructive analysis and does not require any sample preparation. 

Figure 3. Temperature dependence of the specific heat capacities of a Polyamide 6 and of a (PS/SMA2)/PA6 (62/13) 5 blend, measured by thin-film chip calorimetry at different heating rates, after crystallization from the melt at 85 C.

More quantitative infonnation than by calorimetry in Fig. 6.89 could be gained recendy by the use of ultra-fast, thin-film calorimeters based on integrated circuits (see Appendix 10) [55]. Figure 6.90 illustrates the faster recrystallization than crystallization from the random melt, as was also seen for polyethylene in Fig. 6.88. 

FIGURE 2.70 Dependence of bound water versus surface area of titania samples. (Adapted from/. Chem. Thermodynamics, 39, Navrotsky, A., Calorimetry of nanoparticles, surfaces, interfaces, thin films, and multilayers, 2-9, 2007, Copyright 2007, with permission from Elsevier.)... 

Navrotsky, A. 2007. Calorimetry of nanoparticles, surfaces, interfaces, thin films, and multilayers. J. Chem. Thermodyn. 39 2-9. 

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