Free volume vitreous state

During water removal by evaporation, many substances, including proteins and sugars, can be converted to an amorphous state. The temperature at which this transformation takes place is called the glass-transition temperature (Tg), which involves the transition of a liquid-like structured material from an "elastic" or "rubbery" state to a solid "vitreous" one (Roos and Karel, 1991 Roos, 1995). The main consequence of glass transition is an exponential decrease in molecular mobility and free volume as well as... 

During the last few years, attention shifted toward the glassy state, where the performance depends on the extent of freezing the free-volume parameter. The physical aging of vitreous multicomponent systems was interpreted successfully by means of the S-S equation of state. These aspects, along with applications of the S-S equation of state to surface tension and to PALS, are discussed in Chapter 8 and Chapters 10-12, respectively. 

The simplified procedure starts with computation of the characteristic P, 1, V parameters from the PVT data at T> Tg. Next, from Eqs. (14.2) and (14.3), the fictitious hole fraction in the glassy state at T < Tg and P (a prime indicates an independent variable in the vitreous state) is calculated as /lextrapoi = ( P )-Subsequently, from the PVT data at T < Tg, using Eq. (14.2), the hole fraction in the glassy state, hgu = h(T, P ), is computed. Thus, for the same set of T, P, the hole fractions that the melt would have, /lextrapoi, and the factual one, /igiass > extrapoi, are determined. From the isobaric values of h versus T, the frozen fraction of free volume is calculated as [McKinney and Simha, 1974]... 

The parameter FFt is the fraction of the free volume trapped by vitrified segments. Consequently, the nonfrozen fraction, 1 - FFt, is the main contributor to material behavior in the vitreous state. 

Solid body. In amorphous systems, calculate the hole fraction in the vitreous state, h = h P and then the pressure and composition dependencies of the frozen free-volume fraction, FF = FF(P, w). The semicrystalline systems must be treated as supercooled liquids (described by the S-S equation of state) comprising dispersed crystals, described by the Midha-Nanda-Simha-Jain equation of state [see Eqs. (6.32) to (6.34)]. 

Macedo PB, Capps W, Litovitz TA (1966) Two-state model for the free volume of vitreous B2O3. J Chem Phys 44 3357-3363... 

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