liquid has a high surface tension, it generates high levels of residual saturation in the
porous medium (Mercer and Cohen 1990). Interfacial tension is the energy per
interface unit formed between two immiscible liquids. The SI unit (International
System of Units) for surface and interfacial tension is Newton per meter (N m
À1 ).
Wettability and Contact Angle
Wettability describes the extent to which a fluid adheres to the surface of a solid in a
system composed of at least two fluids. The solid has a greater affinity for the fluid
that has the lowest interfacial tension. This “preferred” fluid is called the wetting
fluid. The other fluid, with the higher interfacial tension, is called the non-wetting
fluid (Abdallah et al. 2007; Yuan and Lee 2013). Generally, for DNAPL–water
systems, the DNAPL is considered to be the non-wetting fluid, and water, the
wetting fluid. Wettability can be described and measured by the contact angle (θ)
between the fluids and the solid surface (Hiemenz and Rajagopalan 1997).
Figure 2.6 shows wetting of different fluids. Fluids with a low contact angle
((90
) have high wettability. Those with a high contact angle ()90
) have low
wettability.
For a two-phase incompressible fluid system, such as a DNAPL–water system,
the contact angle between the fluids and the solid surface can be described by the
Laplace–Young equation as shown in Eq. (2.4)[as reported by Nsir (2009)]:
Cosθ ¼
σ NS À σ WS
σ NW
ð2:4Þ
where,
θ: contact angle between the fluids and the solid surface (
)
σ NS : interfacial tension between the non-wetting phase and the solid surface (N m
À1 )
σ WS : interfacial tension between the wetting phase and the solid surface (N m
À1 )
σ NW : interfacial tension between the non-wetting phase and wetting phase (N m
À1 )
The above equation shows that the interfacial tension has an important influence
on the wettability and contact angle. Wettability in the DNAPL–water system can be
affected by several factors, such as the medium’s environmental characteristics [e.g.,
salt concentrations (Kueper et al. (2003)], the presence of surfactants, and the
medium’s saturation history (Mercer and Cohen 1990). Wettability generally
increases—and the contact angle decreases—in DNAPL phases when surfactants
Fig. 2.6 Wetting in different fluids (Yuan and Lee 2013)
2 Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites:. . .
69
porous medium (Mercer and Cohen 1990). Interfacial tension is the energy per
interface unit formed between two immiscible liquids. The SI unit (International
System of Units) for surface and interfacial tension is Newton per meter (N m
À1 ).
Wettability and Contact Angle
Wettability describes the extent to which a fluid adheres to the surface of a solid in a
system composed of at least two fluids. The solid has a greater affinity for the fluid
that has the lowest interfacial tension. This “preferred” fluid is called the wetting
fluid. The other fluid, with the higher interfacial tension, is called the non-wetting
fluid (Abdallah et al. 2007; Yuan and Lee 2013). Generally, for DNAPL–water
systems, the DNAPL is considered to be the non-wetting fluid, and water, the
wetting fluid. Wettability can be described and measured by the contact angle (θ)
between the fluids and the solid surface (Hiemenz and Rajagopalan 1997).
Figure 2.6 shows wetting of different fluids. Fluids with a low contact angle
((90
) have high wettability. Those with a high contact angle ()90
) have low
wettability.
For a two-phase incompressible fluid system, such as a DNAPL–water system,
the contact angle between the fluids and the solid surface can be described by the
Laplace–Young equation as shown in Eq. (2.4)[as reported by Nsir (2009)]:
Cosθ ¼
σ NS À σ WS
σ NW
ð2:4Þ
where,
θ: contact angle between the fluids and the solid surface (
)
σ NS : interfacial tension between the non-wetting phase and the solid surface (N m
À1 )
σ WS : interfacial tension between the wetting phase and the solid surface (N m
À1 )
σ NW : interfacial tension between the non-wetting phase and wetting phase (N m
À1 )
The above equation shows that the interfacial tension has an important influence
on the wettability and contact angle. Wettability in the DNAPL–water system can be
affected by several factors, such as the medium’s environmental characteristics [e.g.,
salt concentrations (Kueper et al. (2003)], the presence of surfactants, and the
medium’s saturation history (Mercer and Cohen 1990). Wettability generally
increases—and the contact angle decreases—in DNAPL phases when surfactants
Fig. 2.6 Wetting in different fluids (Yuan and Lee 2013)
2 Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites:. . .
69