## 3 Results and Discussion
### Phase Separation and Structural Transformation of Polymer Blends at the Nanoscale
Moreover, the reduction of PS\({}^{1}\) viscosity with increasing imprinting temperature can promote the surface-induced phase separation. Figure 7e illustrates the reduction of the polymer melt droplet angles of the PS\({}^{1}\)/PVA (90/10 wt%) blend with increasing temperature. At the temperature of 180 \({}^{\circ}\)C, it was found that the polymer melt droplets had a contact angle lower than 90\({}^{\circ}\) which indicates the oxophilicity with AAO\({}^{2}\) templates. Hence, the surface interaction between polymers and AAO becomes the important role in the phase separation at the imprinting temperature of 180 \({}^{\circ}\)C. Furthermore, thermal-induced flowability of PVA might enhance the formation of PVA droplets on the AAO\({}^{2}\) pore wall due to the low viscosity at above melting temperature. Surface-induced phase separation at the macroscale has been investigated with the annealing process of PS\({}^{1}\)/PVA (90/10 wt%) blend films covered by the AAO template (upper) and aluminum plate (lower) at the temperature of 120-180 \({}^{\circ}\)C for 30 min. The surface chemical properties of the annealed films were simulated using the ATR mapping mode. By the result, the surface film of the polymer blend precursor has the composition of PVA of about \(\sim\)10% (% hydroxyl group). After the annealing process at 180 \({}^{\circ}\)C, the ratio of PVA on the blend film surface adhered on the AAO side was reached about \(\sim\)60-80% but showed the lower ratio on the aluminum side. The increase in the ratio of PVA on the annealed PS\({}^{1}\)/PVA blend film surface indicated the strong surface interaction between PVA and AAO above the melting temperature of PVA, as previously explained for the formation of nanoporous results. This can be confirmed that the formation of the porous PS nanostructured surface is caused by surface-induced phase separation at the imprinting temperature of 180 \({}^{\circ}\)C (See Figure 8). Figure 7: Effect of imprinting temperature on formation of nanoporous (left); (**a**) 120\({}^{\circ}\)C, (**b**) 140 \({}^{\circ}\)C, (**c**) 160 \({}^{\circ}\)C, (**d**) 140 \({}^{\circ}\)C, and (**e**) PS\({}^{1}\)/PVA melt droplets on AAO surfaces (right). According to the coarsening behavior, influences of coarsening temperature (with the function of viscosities and surface tensions) and coarsening times are the crucial parameters to the formation of the porous nanostructures. In this part, the influence of the imprinting time on the formation of the porous nanostructured surfaces will be investigated. The imprinting temperature and pressure of 180 \({}^{\circ}\)C and 5 MPa were performed in the experiment. Figure 9 presents the surface appearances of PS\({}^{1}\) nanostructures obtained from the imprinting time of 15-120 min. With the long imprinting time of about 90-120 min, we found the breakup of the PS\({}^{1}\) nanocolumns into nanofragments due to the agglomeration of the PVA droplets during and after the coarsening behaviors. The agglomeration of PVA droplets depends on the time of diffusion and mass transfer of the PVA. [PERSON] et al. [19] have explained the surface-induced phase separation behaviors by the coarsening process between PMMA and THF confined in AAO templates. The explanation reveals that the coarsening process progressed by the three possible mechanisms consisting of the Ostwald ripening, coalescence, and hydrodynamic flow. The Ostwald ripening was widely used to clarify the phase separation of the polymer solutions. The driving force of this mechanism is to minimize the interfacial energy between the polymer-rich phase and solvent-rich phase or the PS\({}^{1}\)-rich phase and PVA-rich phase for this case. The molecules of the tiny droplets of the dispersed phase dissolve due to the higher curvatures and precipitate on the surface of the large droplets. The reduction of the total  
Figure 8: Annealing behaviors of PS\({}^{1}\)/PVA (90/10 wt%) blends. Figure 9: Effect of imprinting time on the obtained PS\({}^{1}\) nanostructures.