Bound water differential scanning calorimetry

The nature of the water present within a PEM can also have an effect upon its performance during PEMFC operahon. At /I > 6, water exists in the three forms previously mentioned in Section 3.2.1 free water, loosely bound water, and nonfreezable water. This has been established by Eourier transform infrared (FTIR) studies and more recently by calorimetry and gravimetric analysis. Pulse NMR has also been used in conjunchon with differential scanning calorimetry (DSC) to analyze the contributions of these three different types of water in Nation and BPSH membranes. These values can be seen in Table 3.1. 

Although this model has been successful for interpretation of results in a variety of systems, recent studies indicate that it represents an oversimplification" For instance dilatometry, specific conductivity and differential scanning calorimetry results obtained on networks swollen by water can be better descrobed if s of water are assumed bound, interfacial and bulk... 

Walkley, K.1972. Bound water in stratum comeum measured by differential scanning calorimetry. 

Scheuplein s HOHiHOH bonds probably correspond to free water. Bulgin (102) found that differential thermal analysis (DTA) yielded the same 103 °C peak for SC of man or rat and also for wet sand (38). Walkley (103) correlates this peak with frozen free water (which yields latent heat while melting during differential scanning calorimetry). His data show that 30% of SC is bound water that remains after evidence... 

Correlation of total, bound, and surface water in raw materials was the topic of a paper by Torlini and Ciurczak in 1987.The NIR was calibrated by Karl Fischer titration, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA) for the various water types. NIR could distinguish surface from bound water, whereas standard loss on drying (LOD) could not. 

K Nakamura, T Hatakeyama, H Hatakeyama. Studies on bound water of cellulose by differential scanning calorimetry. Tex Res 7 51 607-613, 1981. 

Measurement of Bound (Nonfreezing) Water by Differential Scanning Calorimetry... 

Differential scanning calorimetry (DSC) was used to ascertain the degree, if any, of bound water associated with the PNF polymer. As seen in Table II, the virgin PNF contained 0.01 mg bound water/mg polymer, which increased to 0.05 mg bound water/mg polymer. The reasons for the increase in bound water content as a function of irradiation are currently under investigation (11). This change may be tied to the oxidation level of the polymer. 

Proton-conducting polymer electrolyte membranes based on ACPs such as S-PPBP and sulfonated poly(phenylene sulfide) contain rather large amoimts of bound water. This seems to be the reason for such a sahent featme of these membranes as an increased proton conductivity at high temperatmes and/or low humidities. This conclusion was confirmed by the results of differential scanning calorimetry (DSC) studies of these systems [7]. 

The water potential in SAP has been studied using relaxation time measurement by nuclear magnetic resonance spectroscopy (NMR), and for measurement on freezing and melting temperature, differential scanning calorimetry (DSC) was used [8, 9]. It has been found that the majority of water held by SAP (98-99%) is free water. Semibound water and bound water are known to be 1 to 1.5 kg/kg dry SAP. 

Total amount of water in fibrous materials can be easily measured by use of gravimetric methods. There are also several methods that allow the measurement of the amount of total bound water, such as water retention value (WRV], fiber saturation point (FSC], and differential scanning calorimetry (DSC]. 

In this chapter some problems connected with the utilization of subzero temperature differential scanning calorimetry (SZT-DSC) are discussed. Among them are the determination of hydration numbers of surfactants and organic compounds, the determination of the hydration shell thickness, the effect of alcohol on the distribution of water between free and bound states in nonionic surfactant-based systems, and some considerations regarding the problem of phase separation of such systems in subzero temperatures. The signihcance of SZT-DSC for some novel applications is also discussed. 

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