Chemistry Reference
In-Depth Information
Table 3.10 Effect of HPESO polysoaps on the minimum
equilibrium surface tension of water.
M
w
/kg mol
1
Surface tension/dyn cm
1
Polysoap
HPESO-004K
2.6
19.9
0.6
HPESO-004A
2.6
22.9
0.4
HPESO-003N
3.2
21.6
0.5
HPESO-003K
3.2
19.9
1.1
HPESO-003A
3.2
23.9
1.4
counterion, and 0.186 mM concentration. As can be seen from Figure 3.12,
the surface tension decreases sharply with time initially, then displays a
gradual decrease, and finally levels off to a more-or-less constant value over a
long period of time. This profile is consistent with the generally accepted
mechanism of amphiphile diffusion from the droplet-bulk to the droplet-air
interface. Initially, the concentration of polysoap at the interface is low, and,
as a result, the surface tension is high. This causes rapid diffusion of poly-
soap molecules to the interface, causing a rapid increase in the surface
concentration and a corresponding rapid decrease of surface tension. As the
concentration of the polysoap molecules at the air-water interface ap-
proaches the equilibrium value, the diffusion slows and so the rate of surface
tension declines. After a very long time, the concentration of polysoap at the
interface reaches the equilibrium value and the surface tension become
constant and independent of time. A detailed discussion related to the
surface tension of aqueous HPESO polysoaps was reported in ref. 18.
Table 3.10 shows a summary of HPESO polysoaps on the minimum
equilibrium surface tension of water. It can be seen that the minimum
equilibrium surface tension values of the various aqueous HPESO polysoaps
are in a narrow range of 20-24 dyn cm
1
, indicating that the polysoaps have
similar surface energies.
3.4.5 Interfacial Tension of HPESO Polysoaps between Water
and Hexadecane
Figure 3.13 shows the dynamic interfacial tension between water and hexa-
decane in the presence of a HPESO polysoap. The profile of the time versus
interfacial surface tension data is similar to the time versus surface tension
data discussed earlier. In the presence of a HPESO polysoap in the water, the
water-hexadecane interfacial tension shows an initial fast drop, followed by a
gradual drop and, finally a constant equilibrium value for a very long time. It
should be noted that the equilibrium interfacial tension value is a function of
the concentration of HPESO in the water phase. As demonstrated in
Figure 3.13 the equilibrium interfacial tension decreases with increasing
HPESO concentration in the water phase. Table 3.11 is a summary of the
minimum equilibrium interfacial tension between aqueous HPESO poly-
soaps and hexadecane. From the study of the surface tension and interfacial
