PSI - Issue 26

Chiara Bertolin et al. / Procedia Structural Integrity 26 (2020) 147–154 Bertolin et al. / Structural Integrity Procedia 00 (2019) 000 – 000

152

6

where S ads has been obtained as angular coefficient of the tangential in the t GAB / V ads plot. S GAB is the specific surface areas obtained from eq. 7 =

(7)

with N being the Avogadro number, ρ the water density, σ the average area occupied by one water molecule in the complete monolayer (0.114 nm 2 ) and M is the water molar mass as reported by Timmermann 2003a and Almeida et al., 2007. At the same way, also data obtained from the vacuum microbalance can be expressed in term of thickness of the water film. Table 2 reports the obtained values for the same p / p 0 steps used in the previous discussion. As the relation between t GAB and V ads is linear, it is possible to obtain the angular coefficient of the linear fit, representing the area accessible to water vapor ( S GAB) (Bratasz et al., 2012).

Table 2: t GAB (nm) values for the tested samples at different levels of p / p 0 p/p0 Untreated CS+P40 P40

CS

R

E

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

0.11 0.18 0.24 0.29 0.35 0.42 0.50 0.61 0.77 0.89

0.10 0.16 0.21 0.26 0.31 0.37 0.44 0.53 0.66 0.74

0.09 0.16 0.20 0.25 0.30 0.35 0.42 0.51 0.63 0.71

0.08 0.14 0.19 0.23 0.28 0.35 0.43 0.55 0.73 0.88

0.08 0.14 0.19 0.24 0.29 0.35 0.43 0.54 0.71 0.83

0.06 0.12 0.16 0.21 0.26 0.31 0.37 0.44 0.53 0.58

0.95

The calculated S GAB values are shown in Fig. 3. Variations of this parameter are inversely proportional to the distance between clusters of water molecules on the specimens` surfaces. As observed form Fig. 3 the lowest value is displayed by CS probably meaning that this treatment promotes the formation of smaller water droplets that tend to remain more distant each other. Conversely, E shows the most similar value to that of the untreated pine wood sample

Figure 3: S GAB (left) and S ads (right) values found for the tested samples.