## Discussion

To compare the experimental results with the model and determine whether the homogeneous or composite interface is realized, the contact angle was calculated for the Wenzel Eq. 7.4 and Cassie-Baxter wetting regimes Eq. 7.7. For that end, it was assumed that non-etched sample have smooth matrix (Rfm = 1) and the surfaces roughness is caused by spherical reinforcement particles (Rfr = 2). For etched samples, the matrix roughness is significant in comparison with the reinforcement roughness, although the exact values of Rfm cannot be calculated from the measured Ra. However, it can be estimated as

where L is a typical length of an asperity (Fig. 7.20). For the Cassie-Baxter model we assumed fsLm = 0 (no matrix in contact with water) and fSLr = 1 (entire reinforcement area is covered by water). Assuming L = 10 im, the roughness factors and the contact angles were further calculated (Table 7.3).

It is observed from Table 7.2 that for smoother samples (no etching) the Wenzel model predicts more accurate results, whereas for the etched samples the Cassie-Baxter model is better. As a matter of fact, we decoupled the effects of roughness and reinforcement. The results showed that both roughness and reinforcement are essential for having a superhydrophobic surface. The experimental data show that, for all samples, the contact angle increased with increasing roughness. The change in the contact angle of the Al-graphite sample after etching was greater than that for Cu-graphite. The main reason for this is the difference in their average roughness values, Ra. Since the average roughness values of samples are different for Al- and Cu-graphite composites, respectively, so each sample follows a different behavior.

## Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

## Post a comment