Analysis of Water Sorption Isotherms of Superabsorbent Polymers by Solution Thermodynamics

Analysis of water sorption isotherms of amorphous food materials by solution thermodynamics with relevance to glass transition: evaluation of plasticizing effect of water by the thermodynamic parameters

“…According to the previous works of Kumagai et al, [5][6][7] the integral Gibbs free energy ΔG s (the change in Gibbs free energy due to water sorption) is the most suitable parameter for evaluating the interaction between the material and water among the free energies DG s a , DG s w , and ΔG s obtained using solution thermodynamics from water sorption isotherms. As per these reports, DG s a is the contribution of "change in state of solid" to the change in Gibbs free energy of the system ΔG s , according to Equations (7) and (8), previously described in this paper.…”

“…The equations of solution thermodynamics described here are almost the same as in the work of Kumagai et al [5][6][7] When solution thermodynamics is applied to water sorption isotherms (plot of water content (W) against water activity (a w )), the condensed phase formed by water sorption to the adsorbent (solid) is taken as the solution. The reference state for water is the liquid form under the solution temperature (T) and pressure (P), and that for the adsorbent is a pure solid at T and P. In addition, thermodynamic variables are expressed in mass units, because the water sorption data are usually obtained on a mass basis.…”

“…[8][9][10][11] From a thermodynamic equation shown later in this report, DG s a is taken to be the contribution of "change in state of solid" to the change in Gibbs free energy ΔG s . According to the reports of Kumagai et al, [5][6][7] DG s a greatly contributed to ΔG s at high water content, probably due to changes in the solid material. However, relation between the observed changes in the state of solid by water sorption (e.g.…”

“…Kumagai et al have analyzed the water sorption isotherms of some foods and superabsorbent polymers using solution thermodynamics. 6,7) Subsequent works analyzed the water sorption behavior of moistened food in the region of high water content by regarding it as solution. [8][9][10][11] From a thermodynamic equation shown later in this report, DG s a is taken to be the contribution of "change in state of solid" to the change in Gibbs free energy ΔG s .…”

Changes in Activity Coefficient γwof Water and the Foaming Capacity of Protein during Hydrolysis

“…1) In order to obtain quantitative information, the analysis of a water sorption isotherm by solution thermodynamics is eŠective, as discussed in our previous studies. [2][3][4] Some important parameters such as a change in the Gibbs free energy during water sorption can be obtained. However, water activity aw depends not only on the a‹nity of each solute molecule for water, but also on the number of solute molecules in the system, as explained in a subsequent part of this paper.…”