Handbook of Solvents - George Wypych - ChemTech - Ventech!

342 George Wypych
ξ
0.55
0.5
0.45
0.4
0.35
0.3
0.25
0.2
1
0.15
30 40 50 60 70 80 90 100
Solvent molar volume at 0K, cm 3 mole -1
Figure 7.1.3. Parameter ξ vs. solvent molar volume. 1 -
methanol, 2 - acetone, 3 - methyl acetate, 4 - ethyl
acetate, 5 - propyl acetate, 6 - benzene, 7 - toluene, 8 -
ethylbenzene. [Adapted, by permission, from D
Arnauld, R L Laurence, Ind. Eng. Chem. Res., 31(1),
218-28 (1992).]
Flux, μg cm 2 s -1
20
15
10
5
2
6 7
3
benzene
0.4
0
acetone
0.2
-5
0 20 40 60 80
0
100
Time, min
4
8
5
1.4
1.2
0.8
0.6
Figure 7.1.5. Flux vs. time for two solvents. [Adapted by
permission from C F Fong, , Y Li, De Kee, J Bovenkamp,
Rubber Chem. Technol., 71(2), 285-288 (1998).]
1
Diffusion coefficient, cm s -1
Figure 7.1.4. Mutual and self-diffusion coefficients
for polystyrene/toluene system at 110 o C. [Adapted, by
permission, from F D Blum, S Pickup, R A Waggoner,
Polym. Prep., 31 (1), 125-6 (1990).]
Many experimental methods such as
fluorescence, reflection Fourier transform
infrared, NMR, quartz resonators, and
acoustic wave admittance analysis, are
used to study diffusion of solvents. 4-11 Special
models have been developed to study
process kinetics based on experimental
data.
Figure 7.1.4 shows the effect of concentration
of polystyrene on mutual and
self-diffusion coefficients measured by
pulsed-gradient spin-echo NMR. The data
show that the two coefficients approach
each other at high concentrations of polymer
as predicted by theory. 4
Studies on solvent penetration
through rubber membranes (Figure 7.1.5),
show that in the beginning of the process,
there is a lag time called break-through
time. This is the time required for solvent to begin to penetrate the membrane. It depends on
both the solvent and the membrane. Of solvents tested, acetone had the longest
break-through time in natural rubber and toluene the longest in nitrile rubber. After penetration
has started the flux of solvent increases rapidly and ultimately levels off. 7 This study is
relevant in testing the permeability of protective clothing and protective layers of coatings.
10 -4
10 -5
10 -6
10 -7
10 -8
10 -9
mutual
self
0 20 40 60 80 100
PS, wt%