Effect of an Electric Field on the Surface Tension of a Dipolar-Quadrupolar Fluid and Its Implication for Sign Preference in Droplet Nucleation

The effect of a uniform electric field on interfacial properties of dipolar-quadrupolar fluids is investigated by using the density-functional theory. As in the case of purely dipolar fluids the (thermodynamic) surface tension is always altered by the external field, regardless of the direction of the field. However, unlike the purely dipolar fluids, for two given external fields with the same strength but exactly opposite direction the magnitude of variation in the surface tension is different. This apparent symmetry breaking by reversing the field direction suggests a new molecular mechanism to explain the phenomenon of sign preference in droplet formation on charged condensation centers.

Figure 1

The orientation order parameter ${\eta }_1$ at vapor-liquid coexistence for two given external fields. The right branch with larger values of ${\eta }_1$ corresponds to the vapor phase and the left branch corresponds to the liquid phase.

Figure 2

Interfacial order-parameter profile ${\eta }_1(z)$ at $T^{*}=1.96$ for various given strengths and signs of external field.

Figure 3

Interfacial order-parameter profile ${\eta }_2(z)$ at $T^{*}=1.96$ for various given strengths and signs of external field.

Figure 4

Temperature dependence of the reduced surface tension ${\sigma }^{*}=\sigma d^2/ϵ$ for zero field and two nonzero fields that are normal to the interface but with the exact opposite direction.