## 3 Results and Discussion
### Fabrication of One-dimensional Nanostructures by Thermal Nanoimprint  
In this part, the flowability and confinement effects of PS1 and PS2 at the nanoscale will be clarified. Figure 3 shows representative SEM images (side view) of PS1-VANs and PS2-VANs obtained by thermal nanoimprint using the AAO1 template. For the each of the SEM images, PS1-VANs and PS2-VANs were produced using the imprinting conditions of 180 \({}^{\circ}\)C, 5 MPa, for 30 min. The crucial point for performing the thermal nanoimprint is that the imprinting temperatures must be above \(T_{g}\) or \(T_{m}\) of the polymers which is sufficient for chain mobility and adequate for flowability at the nanoscale in AAO cavities. In Figure 3, PS1-VANs and PS2-VANs with lengths of 70 and 40 \(\upmu\)m respectively can be produced. The obtained VANs, having bundle-like structure, exhibit orderly array structures but the tendency to agglomerate. The appearance of agglomerated nanostructures is explainable by surface adhesion induced between individual nanostructures. Generally, the quality of agglomerated nanostructures was enhanced by using lower aspect ratios and higher interpore distances in AAO templates. Figure 2: Scanning electron microscopy (SEM) images of surface morphologies of (**a**) AAO1 (**b**) AAO2 and (**c**) cross–sectional AAO2. As Figure 3, the difference in the length of VANs due to the different flowability of the PS precursors in the range of 160-220 \({}^{\circ}\)C is shown, with fixed imprinting pressure and imprinting time of 5.0 MPa and 30 min respectively. The longer length of PS\({}^{1}\)-VANs is compared with PS\({}^{2}\)-VANs, due to the higher MFR and lower \(T_{g}\) of PS\({}^{1}\). The lower value of \(T_{g}\) indicated higher chain mobility of polymer due to larger free-volume of the polymer chain packing. The PS\({}^{1}\) showed the higher flowability within AAO\({}^{1}\) templates as compared with PS\({}^{2}\). The flowability of the polymers was enhanced by increased imprinting temperature due to the reduction of polymer viscosities, and decreased surface tensions between polymer melts and AAO templates [11; 12; 13; 14; 15]. However, the length of VANs did not increase at temperatures above 180 \({}^{\circ}\)C because the polymer was easily ejected out from the AAO nanocavities under the high imprinting pressure and relatively low viscosity. PS\({}^{1}\)-VANs and PS\({}^{2}\)-VANs of about 15-72 \(\upmu\)m long were obtained depending upon the imprinting conditions. The flowability at the nanoscale of the molten polymers in the AAO templates driven by the imprinting process is in agreement with the Hagen-Poiseuille expression [15; 50]. The length (\(H\)) or distance the polymer flowed through AAO can be estimated as shown below. \[H=2r\sqrt{\frac{\left(P+\frac{2\gamma\cos\theta}{r}\right)t}{32\eta}} \tag{1}\]  
This equation shows that the factors related to flowability in confined spaces are imprinting pressure (\(P\)), radius of the nanochannel (\(r\)), surface tension of the molten polymer (\(\gamma\)), contact angle of the polymer on AAO pore wall (\(\theta\)), viscosity of the molten polymer (\(\eta\)), and infiltration time (\(t\)). Our previous study revealed that the reduction of apparent viscosity estimated by Equation (1) may be the result of shear rate, wall slip, and the pressure used in the imprinting process [15]. To avoid the effects of confinement on the phase separation and transformation behaviors at the nanoscale, therefore, we investigated this change in molecular free-volume by analyzing the thermal properties of obtained PS-VANs as compared with PS bulk films. Specimens were obtained by imprinting conditions of 180 \({}^{\circ}\)C, 5 MPa, for 30 min with different AAO pore size and \(T_{g}\) of polymers. Figure 4 shows the DSC heating thermograms of the PS bulk films and PS-VANs. The results indicate a change in molecular free-volume was found in the case of PS\({}^{2}\)-VANs when using AAO\({}^{1}\) templates.