## 3 Results and Discussion
### Surface Properties  
Surface properties of polymers were evaluated using the water droplet angle measurement, macroscale friction test, and nanoindentation. The five types of polymer films used to investigate were; (1) neat PS\({}^{1}\), (2) neat PVA, (3) PS\({}^{1}\)/PVA (90/10 wt%) blend, (4) PS\({}^{1}\)-VANs, and (5) PS\({}^{1}\)-VAPNs. The imprinted samples were obtained using the imprinting condition of 180 \({}^{\circ}\)C, 5 MPa for 30 min (nanostructures length \(70\pm 10\) um with the remained film thickness \(40\pm 10\) um).  
The results of the water droplet angle measurement was presented in Figure 13. The flat surfaces of PS\({}^{1}\) and PVA films with the droplet angle of water about \(\sim\)89.8\({}^{\circ}\) and \(\sim\)40\({}^{\circ}\)-50\({}^{\circ}\) (initial droplet) were obtained. The water-soluble properties of the PVA influence the instability of the water droplet shape and its angle as shown on the shadow side of the water droplet. The water droplet angle of PS\({}^{1}\)/PVA film with a value of about \(\sim\)65.6\({}^{\circ}\) can be measured. PS\({}^{1}\)-VANs surface shows the water droplet angle reach \(\sim\)130.1\({}^{\circ}\). The great increase in water droplet angle as compared to the flat films is the result of the physical roughness of the nanostructures and the reduction of the contact area between polymer and water droplet. Moreover, the PS\({}^{1}\)-VAPNs surface has a slight increase in the water droplet angle to \(\sim\)140.1\({}^{\circ}\) as compared with the PS\({}^{1}\)-VANs due to roughness at the nanoscale.  
Figure 12: Transformation of polymer nanostructures driven by the Rayleigh instability.  
Figure 13: Water droplets on the polymer surfaces.  
Surface friction properties at macroscale demonstrated the same tendency with results of the water droplet angle measurement. The measured friction coefficients was placed in Figure 14. The PS\({}^{1}\)-VAPNs surfaces exhibit the higher friction coefficient (\(\sim\)0.53-0.55) as compared with PS\({}^{1}\)-VANs surface (\(\sim\)0.37-0.42). The results indicate the roughness at the nanoscale influences the changes in surface friction at the macroscale, and the surface energy in the water droplet angle measurement as in the explanation above [53; 54; 55; 56]. In addition, the friction coefficient of PS\({}^{1}\)-VAPNs can be enhanced when it was switched to the wetting condition. This result is due to the water bridge-mediated contact formation induced by the solid-solid contact between the contact elements and the porous surface of PS\({}^{1}\)-VAPNs [9; 10].  
By the results of the nanoindentation test, the PS\({}^{1}\)-VAPNs show a lower surface hardness and surface modulus as compared with PS\({}^{1}\)-VANs due to the scaling down or the size reduction effect of the material structures after the removal of the PVA segment [57]. Hence, the size reduction has the result of a decrease in the energy absorption capacity and the destruction of the nanostructures becomes easier. The surface hardness of 0.6 and 0.8 MPa and surface modulus of 0.03 and 0.08 GPa of the PS\({}^{1}\)-VAPNs and PS\({}^{1}\)-VANs can be respectively obtained using the indentation test. Figure 15 presents the nanoindentation test results of the imprinted nanostructures.  
Figure 14: Friction coefficients of polymer surfaces  
Figure 15: Nanoindentation test results.