Effect of temperature on the dynamics and geometry of reactive-wetting interfaces around room temperature

The temperature effect on the dynamics and geometry of a mercury droplet (∼150 μm) spreading on a silver substrate (4000 Å) was studied. The system temperature was controlled by a heating stage in the temperature range of −15 °C < T < 25 °C, and the spreading process was monitored using an optical microscope. We studied the wetting dynamics (droplet radius and velocity) as a function of temperature. We found that for all studied temperatures, the spreading radius R($t$) grows linearly with time, with a velocity value depending on temperature. We also studied the temperature effect on the kinetic roughening properties of the advancing interface (growth (β) and roughness (α) exponents). Our results show that the growth exponent increases with temperature while the roughness exponent is relatively constant. In addition, we obtained the system's activation energy at this temperature range.

Figure 1

Mercury viscosity versus temperature (after Ref. [6]).

Figure 2

Schematic description of a mercury droplet spreading on a silver substrate.

Figure 3

Interfaces described by $h(x,t)$ for two typical times, $t_2>t_1$.

Figure 4

A typical interface at a specific time.

Figure 5

The experimental setup.

Figure 6

Pictures 1–13. Successive snapshots of the growing interface for a single experiment at $T=-15{}^{\circ }\mathrm{C}$. The time interval between snapshots is 2 s. The scale of each snapshot is 25×6.179 μm.

Figure 7

$R\left(t\right)$ (log-log scale), $T=-15{}^{\circ }\mathrm{C}$, single experiment.

Figure 8

The droplet spreading velocity vs. temperature.

Figure 9

W($t$) (log-log scale), $T=-15{}^{\circ }\mathrm{C}$, single experiments. The arrows indicate the growth regime. The growth exponent β is calculated by a linear fit of the growth regime.

Figure 10

β values vs. temperature. β increases with temperature. The result at room temperature coincides with Efraim et al. [20, 21].

Figure 11

The last snapshot of an experiment, $T=-15{}^{\circ }\mathrm{C}$. Picture scale is 25×12.075 μm.

Figure 12

W(L) (log-log scale), $T=-15{}^{\circ }\mathrm{C}$, single experiment.

Figure 13

The activation energy in the mercury-silver system around room temperature.