## 3 Results and Discussion
### Comparison of Tribological Properties between Pristine and Microtextured Surfaces  
Microscopic measurements recording friction vs. normal force curves on Thordon and polyurethane with pristine and microstripe-textured surfaces were recorded by AFM. The results are shown in Figure 8. The scanning size was set to 50 \(\upmu\)m \(\times\) 50 \(\upmu\)m. For each measurement, a friction loop [25] was recorded for the AFM tip scanning in the forward and backward directions with a varying normal force. The averaged friction forces for both directions were calculated. For each sample, three different positions were analyzed, and the results were averaged into each single data point in Figure 8. Increasing the defined normal force \(F_{\text{load}}\) and recording the frictional force \(F_{\text{fric}}\), the friction coefficient \(\mu\) can be calculated by linearly fitting the applied load and its corresponding friction data (\(F_{\text{fric}}=F_{\text{adh}}+\mu\times F_{\text{load}}\)). As shown in Figure 8, the data show a nearly linear relationship between the normal loads and friction forces. The friction coefficient \(\mu\) was calculated as the slope of this linear fit (provided in the legend) and was compared between the results for the pristine and microstripe-textured surfaces. For polyurethane, the friction coefficient of the pristine surface decreased from 1.83 to 0.99 with the introduction of a microstripe-textured structure, and this value decreased from 2.36 to 1.25 for the Thordon. This suggests that the presence of microstripe textures can effectively reduce the friction on water-lubricated materials. Figure 8: AFM-based friction measurement of Thordon and PU with pristine and microstripe-textured surfaces. The straight line in the figure was fitted to obtain the slope of the line, i.e., the friction coefficient \(\upmu\). Figure 9 shows the friction (Figure 9a), average coefficient of friction (COF), and specific wear rate (Figure 9b) of the above samples for the 2 h friction test conducted at a 50 N load, 100 r/min rotary speed, and water lubrication in the ring-on-block friction/wear test. As shown in Figure 9a, the friction of all Thordon samples was greater than that of the polyurethane samples. In addition, compared to Thordon, the friction trend of polyurethane was more stable over time, while the friction jitter amplitude of Thordon was larger, which was determined by the material's properties. Combined with the analysis of the surface morphology after abrasion, this is due to the fact that the abrasion mark on Thordon is deeper than that on polyurethane, by about 8-9 times. In particular, it is interesting to note that for the same material, surfaces with microstrip textures always exhibited lower friction than the pristine surfaces. This suggests that the microstrip texture contributed to the reduction in friction on the water-lubricated materials. Figure 9b shows that the samples with microstrip-textured surfaces demonstrated a lower coefficient of friction and wear rate relative to the samples with pristine surfaces. The COFs of Thordon and PU with microstrip-textured surfaces were reduced by about 17.7% and 19.8%, respectively, compared to the pristine surfaces. In terms of wear performance, the wear rates of Thordon and PU with microstrip-textured surfaces were reduced by 27.3% and 25.5%, respectively, compared to those of the samples with pristine surfaces. The excellent tribological properties of microstrip-textured surfaces can be attributed to several factors. Firstly, the microstructure reduces the actual contact area and adhesion between the friction pairs, resulting in lower friction. In addition, the microtexture, with a depth of 0.5 um between the stripes, helps to trap abrasive particles and can reduce the occurrence of abrasive wear.