*4.1. Thickness of the Film*

The key emphasis in this article is on furnishing a shiny metallic layer of nanoparticles, suspended with different base fluids displaying distinct physical and chemical features altogether. Here, the sole aim is to decide which one of the base fluids is the best suitable choice for this metallic covering over the disk with spin coatings that can quickly spread on the disk in a short span of time. As shown in Figure 2, it can clearly be seen that ethanol is the sole liquid which shows a rapid action with both metals as compared to the other base fluids. It is in accordance with their physical prospects, due to their densities, which help them evaporate quickly and results in a shiny metallic nanoliquids coating on the disk. On the other hand, silver particles' coating is much faster than gold, as Figure 3 shows.

**Figure 2.** Behaviour of film thickness for different base fluids containing gold nanoparticles.

**Figure 3.** Behaviour of film thickness for different base fluids containing silver particles

In Figures 4–7, thermocapillary parameters and the concentration of the metallic particles' influence on nanofluid coating have been displayed. It is a well-recognized fact that the thicker solution yields to the thicker layer of the film. The thermocapillary parameter depletes and attenuates this metallic layer as shown in Figures 4 and 5. From the above given facts, it is inferred that ethanol and silver particles share a great deal of mutual compatibility. Thickness of the film increases in size upon the additional supply of metallic particles as shown in Figures 6 and 7. This confirms the above preceding claim that an increase of the particles will enlarge the film thickness in size. Therefore, it can be concluded that any fluids and particles which exhibit different characteristics like ethanol and silver are regarded as the most suitable option for this metallic process of coating. Consequently, to see the effects of thermal, radial and azimuthal velocity, ethanol was chosen as a base fluid.

**Figure 4.** Behaviour of film thickness for thermocapillary parameter for gold particles.

**Figure 5.** Behaviour of film thickness for thermocapillary for silver particles parameter.

**Figure 6.** Effects of the concentration of particles on film thickness for the case of gold.

**Figure 7.** Effects of the concentration of particles on film thickness for the case of silver.

#### *4.2. Radial Velocity and Azimuthal Velocity*

In Figures 8–21, the radial and azimuthal velocities have been sketched for all base fluids, the thermocapillary parameter and the concentration of the particles. In view of suitable transformation, the mathematical expressions take the following final form:

$$\mathcal{U}I(z,t) = \mathbb{R}\,\,F(z,t)\tag{58}$$

$$V(z,t) = \mathbb{R}\,\,\mathrm{G}(z,t)\tag{59}$$

**Figure 8.** Behavior of radial velocity for each fluid comprising gold particles.

**Figure 9.** Behavior of radial velocity for each fluid comprising silver particles.

**Figure 10.** Behavior of radial velocity for the thermocapillary parameter comprising gold particles.

**Figure 11.** Behavior of radial velocity for the thermocapillary parameter comprising gold particles.

**Figure 12.** Effects of concentration particles on radial velocity with gold particles.

**Figure 13.** Effects of concentration particles on radial velocity with silver particles.

**Figure 14.** Behavior of azimuthal velocity for each fluid with gold particles.

**Figure 15.** Behavior of azimuthal velocity for each fluid with silver particles.

**Figure 16.** Behavior of azimuthal velocity for the thermocapillary parameter with gold particles.

**Figure 17.** Behavior of azimuthal velocity for the thermocapillary parameter with silver particles.

**Figure 18.** Effects of concentration particles on azimuthal velocity for gold.

**Figure 19.** Effects of concentration particles suspended with ethanol on *N* for silver.

**Figure 20.** Temperature effects of thermocapillary parameter.

**Figure 21.** Temperature effects of thermocapillary parameter.

In Equations (58) and (59), *R* = *<sup>r</sup> <sup>h</sup>*<sup>0</sup> is the initial thickness of the film. A similar trend in the behavior of both types of velocities is observed in the presence of silver and gold particles.

In Figures 8–19, the behavior of ethanol is quite prominent for all cases. It is observed that the radial velocity and azimuthal velocity increase for silver and gold. However, radial velocity and azimuthal velocity react quite differently for the thermocapillary parameter and the concentration of the particles. It is seen that temperature increases by increasing the values of thermocapillary parameter, as shown in Figures 20 and 21. It is in accordance with the physical expectation because radial velocity does not allow the fluid to move with full strength. However, the radial velocity is supported by the thermocapillary parameter. On the other hand, a complete reverse trend can be noted for the azimuthal velocity by varying both *α* and *ϕ*.
