Table 1.
Mixture compositions for glass transition studies.
Table 2.
Relative humidity values at room temperature for saturated salt solutions [32].
Fig 1.
Representative DSC data (A) and zoomed in version showing the glass transition region (B).
Light grey line is the initial ramp up in temperature which is done to erase thermal history in the sample. The test proceeds counter-clockwise, as indicated by the arrows. The glass transition temperature was determined from the inflection point in the second heating cycle, as illustrated in panel B (arrow).
Fig 2.
Moisture content in samples prepared either as an aqueous solution (black symbols) or as a freeze-dried matrix (white and grey symbols) was measured after equilibration in chambers with controlled relative humidity. The BET model (Eq 3) was fit (dotted lines) to observations from freeze-dried samples, except for the trehalose-PBS case, in which aqueous solution data were used for fitting; in the trehalose-water experiment, outlier values at 75% relative humidity (grey symbols) were omitted from the fit. See Table 1 for detailed composition of each mixture.
Fig 3.
Glass transition temperature of binary trehalose-water mixtures.
Samples were prepared either by equilibrating aqueous solution (black symbols) or freeze-dried matrix (white symbols) in various relative humidity environments. The solid grey line shows a fit of the GT model to literature data, as reported by Chen et al. [29]. The dotted line shows the best-fit GT model (Eq 1) to the data from the current study. The dashed line represents predictions of the CK model (Eq 2) using the parameters shown in Table 3.
Table 3.
Parameters for use in the CK model.
Fig 4.
Glass transition temperature of trehalose-PVP-water mixtures.
Samples were prepared by equilibrating freeze-dried matrix in various relative humidity environments. The dotted line shows the best fit of the GT model (Eq 1) to the data. The solid line shows predictions of the CK model (Eq 2) using the parameters shown in Table 3.
Fig 5.
Glass transition temperatures of various mixtures containing PBS.
Samples were prepared either by equilibrating aqueous solution (filled symbols) or freeze-dried matrix (open symbols) in various relative humidity environments. The dotted lines show the best-fit GT model to each data set. Mixtures containing penetrating CPAs at concentrations of 0.25 M and 0.5 M are shown as circles and triangles, respectively. See Table 1 for detailed composition of each mixture.
Fig 6.
Comparison of best-fit GT models.
(A) Effect sugars, polymers and PBS salts on the glass transition temperature. (B) Effect of CPAs on the glass transition temperature.
Table 4.
Best-fit GT model parameters (see Eq 1).