Weakly bound water

Free Moisture. The free moisture of a filler is the water present on the surface of the particles. This weakly bound water can sometimes contribute to iaterparticle bonding (reinforcing) or filler—matrix iateraction, ie, biader adsorption or catalysis. A determination of free moisture is usually made by measuriag the percent loss on drying the sample at either 100 or 110°C. 

Lioutas et al. (1986) measured the 0 and resonances of lysozyme powders and solutions, in experiments like those carried out for H by Fullerton et al. (1986). They similarly interpreted discontinuities in the NMR response in terms of three populations of water 20 mol of water per mol of protein (corresponding to 0.025 h) with a correlation time of 41 psec, 140 mol of water (0.17 h) with a correlation time 27 psec, and 1400 mol of water (1.7 h) with a correlation time 17 psec. The differences between these results and those of Fullerton et al. (1986) indicate the difficulty of estimating water correlation times. Lioutas et al. (1987) extended these results by analyzing H resonance data through comparison with the sorption isotherm. D Arcy-Watt analysis of the sorption isotherm gave 19 mol of tightly bound water per mol of lysozyme, 148 mol of weakly bound water, and 2000 mol of multilayer water. These classes plus two more types, corresponding to water in solutions... 

Figure 4 Examples of the differential sorption heat calculated from the sorption data using the Clausius-Clapeyron equation. The arrows depict the most negative enthalpy value in the region of strongly (SP) and weakly (WP) bound water, the limit of the strongly bound water region (SBC), the moisture content where bound water first appeared (BWiso), and the tissue moisture range corresponding to weakly bound water (WBC) [56].

The effects of drought, i.e., the quantitative properties of water in fresh and dry leaves of durum wheat were tested by the relation between the water status and the properties of bound water (BW) with different strengths to ionic, polar, or hydrophobic sites of macromolecules [56]. An increase in tissue affinity for strongly bound water implied a simultaneous increase in the affinity for weakly bound water. The qualitative properties of bound water may be particularly important for drought adaptation in durum wheat, which is associated with solute potential plots of differential energies of water sorption (Figure 4). 

Colloids are best precipitated from hot, stirred solutions containing sufficient electrolyte to ensure coagulation. The filterability of a coagulated colloid frequently improves if it is allowed to stand for an hour or more in contact with the hot solution from which it was formed. During this process, which is known as digestion, weakly bound water appears to be lost from the precipitate the result is a denser mass that is easier to filter. 

Fig. 8. Model of the structure of thallium(I) carboxylate species in highly concentrated aqueous solutions. Temperature = 25°C. (a) Formate species. [Tl]t t = 10.8 M, [H2O]/ [TKD] = 2.6, [formate ]/[Tl(I)] = 1.0. Thalliumd) ions are fourfold coordinated by three formate oxygens and one weakly bound water molecule (not shown), (b) Malonate species. [TlJtot = 9-0 M, [H20]/[T1(D] = 3, [malonate "]/[Tl D] = 0.5. Fourfold oxygen coordination of thalliumd) ion is shown only for one T1(I) atom. Some interatomic distances are given (in angstroms). From Yamaguchi et al. 177).

The crystal structure shows a marked difference in the copper environments in the two monomers. In one of the subunits two electron density maxima are observed riding the cuprous ion in place of the usual density expected for the weakly bound water molecule. This is a two-center density that can be modeled with two water molecules at full occupancy, each being at coordinating distance from the metal ion, resulting in the imusual geometry shown in Fig. 11. The electron density could not be unambiguously interpreted because it can be modeled as well by a disulfide anion at about half occupancy. Such an anion may have been originated from the dithionite used for copper reduction. 

The total volume of weakly (C ) and strongly (Cuw) bound waters (unfrozen at T < 273 K) at the silica interfaces (Table 38.5) is markedly larger than Vp (but significantly lower than Vemp) with one exception for SI-6 (Table 1). With increasing specific surface area of the first series samples, there is tendency of reduction of the free surface energy (Table 5, js) and the amount of weakly bound water Besides, the AG Cuw)y... 

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