Glass transition water heat capacity

Matveev, Y. I., Elankin, N. Y., Kalistrova, E. N., Danilenko, A. N., Niemann, C., and Yuryev, V. P. (1998). Estimation of contributions of hydration and glass transition to heat capacity changes during melting of native starches in excess water. Starch/Starke 50, 141-147. 

The data for the crystal structure, NMR structure, powder x-ray diffraction pattern, water vapor sorption isotherms, glass transition temperature as a function of water, heat capacity, heat of solution properties, vapor pressure, and osmotic pressure are described in the literature. 

The glass-transition temperature, T, of dry polyester is approximately 70°C and is slightly reduced ia water. The glass-transitioa temperatures of copolyesters are affected by both the amouat and chemical nature of the comonomer (32,47). Other thermal properties, including heat capacity and thermal conductivity, depend on the state of the polymer and are summarized ia Table 2. 

Fig. 17. Temperature variation of internal energy. Et (kj mole"1), coordination number (CN), and gmi /gm.x ratios of water showing the occurrence of the glass transition in the 200-240 K range. Volume also shows a similar change, but a slightly lower temperature. In the inset, variation of the configurational heat capacity, Cp (J deg 1 mole-1), with temperature is shown. (From Chandrasekhar and Rao (73).)...

Hutchens et al. (1969) determined the heat capacities of zinc insulin at 0 and 0.04 h and of chymotrypsinogen A at 0 and 0.107 h, from 10 to 310 K. For all samples the data were a smooth function of temperature, with no indication of a glass or phase transition at any temperature. The absence of a phase transition corresponding to the ice-liquid water transition is expected for low hydrations. These appear to be the only data in the literature that have been used to determine the entropy of a protein sample. Hutchens et al. (1969) calculated the standard entropy of formation of a peptide bond as 9.0—9.3 cal K mol" . 

Andronikashvili et al. (1979) measured the heat capacity of collagen at 0 and 0.4 h, from 4 to 320 K. Neither sample showed an ice-liquid water phase transition. The anhydrous sample showed a smooth increase in heat capacity with temperature. The hydrated sample showed a discontinuity at 120 K, apparently associated with an order—disorder transition, perhaps a glass transition, above which there was a 10-fold stronger dependence of the heat capacity on temperature. 

Usha and Wittebort (1989) studied the NMR of crystalline cram-bin. At 140 K the protein hydrate is stationary, with t = 1 msec. Above 200 K changes in the signal with temperature are consistent with a glass transition or melting of the hydration water. This broad transition parallels closely the changes with temperature found for the heat capacity, Mossbauer spectroscopic, and other properties of hydrated protein crystals. At room temperature no more than 12 water molecules are orien-tationally ordered. The average rotational correlation time of the hydration water is about 40 times longer than that for bulk water. 

The evolution in calorimetry technology has also led to the development of protocols for quantitative analysis (Buckton and Darcy 1999). Fiebich and Mutz (1999) determined the amorphous content of desferal using both isothermal microcalorimetry and water vapour sorption gravimetry with a level of detection of less than 1 per cent amorphous material. The heat capacity jump associated with the glass transition of amorphous materials MTDSC was used to quantify the amorphous content of a micronised drag substance with a limit of detection of 3 per cent w/w of amorphous... 

The Tg curves for the water-maltodextrin-sucrose system was plotted using the expanded Gordon-Taylor model (Equation 21.1) for ternary systems, considering the variation in heat capacity for water (ACpi) equal to 1.94 J/g °C (Kalichevsky and Blanshard, 1993) and for sucrose (ACp2) equals to 0.60 J/g °C (Roos, 1993). The value for ACps of 0.24 J/g °C used here for maltodextrin MOR-REX 1910 was estimated from considering the value for k (the ratio of changes in the water and solid heat capacities at Tg) to be equal to 8.055. Table 21.1 shows the parameters used to determine the glass-transition curves for the maltodextrins, with and without additives (sucrose). 

The depressed glass transition temperatures of the resin at various concentrations of sorbed water were determined using scanning calorimetry. Samples of the resin were first conditioned with an excess of water in large volume stainless steel DSC pans at predetermined temperatures then scanned at 20 deg/min. Heat capacity measurements were also made with a Perkin-Elmer OSC-2 scanning calorimeter. 

---