## 3 Results and Discussion  
### Characterization of the Plasma-Treated Surfaces  
Contact angles are measured for each plasma-treated substrate using an optical contact angle analyzer (Phoenix 300, Surface Electro Optics Co., Ltd., Suwon, Gyeonggi-do, Korea). The five test liquids used for the measurement are as follows: two polar liquids (water and formamide (Sigma-Aldrich Corp., St. Louis, MO, USA)), two non-polar liquids (diiodomethane (Sigma-Aldrich Corp., St. Louis, MO, USA) and tetradecane (Sigma-Aldrich Corp., St. Louis, MO, USA) and a tetradecane based Ag colloidal suspension. Figure 2 presents the results of the contact angle measurement. Between the polar-liquids and the non-polar liquids, the fluctuation of contact angles was more dominant in the former than the latter. Moreover the contact angle decreased overall as the substrate type varied from a hydrophobic \(S\) 30 to a hydrophilic \(S\) 90. Among the substrates, the \(S\) 30 showed the largest contact angle for all the test liquids. Particularly the \(S\) 70\({}^{1}\) had much larger contact angle than the \(S\) 50 and the \(S\) 70\({}^{2}\) substrate, deviating from the general trend. This anomalous behavior will be explained in terms of the surface characteristics of the substrates in the following.  
Figure 3 presents the high-resolution XPS spectra of C1s core level of the fluorocarbon polymeric film deposited on the other substrates except the \(S\) 90. The C1s spectra were decomposed into five components to determine the chemical composition of the film-coated substrate surfaces: C-C (284.6 eV), C-CF (286.6 eV), CF-CF\({}_{2}\) (288.9 eV), CF\({}_{2}\) (291.2 eV) and CF\({}_{3}\) (293.3 eV). The \(S\) 30 substrate contained a larger amount of C-F\({}_{\rm x}\) moieties than the \(S\) 50 and \(S\) 70 substrates. Also the intensity of the C-F\({}_{\rm x}\) moieties decreased as the hydrophilicity of the plasma-treated substrate increased. The C-C bond began to appear in the chemical composition of the two \(S\) 70 substrates because of the defluorination induced by the O\({}_{2}\) plasma etching which eliminates the CF\({}_{2}\) and CF\({}_{3}\) species. The F/C ratio of each substrate decreased from 1.89 to 0.43. This is in good agreement with the overall transition of the measured contact angles.  
The surface topology after the plasma surface treatment was examined using SEM and AFM, as in Figure 4. The SEM images and the corresponding AFM images present that the \(S\) 70\({}^{1}\) and the \(S\) 70\({}^{2}\) possess a remarkable difference in the surface topology although they have the similar droplet diameter and F/C ratio. The \(S\) 70\({}^{1}\) substrate has numerous hillocks on the fluorocarbon film, compared to the \(S\) 70\({}^{2}\) substrate. However, the difference of the surface roughness does not seem to make the difference in contact angle between the two substrates because it cannot explain the difference of contact angle between the polar and non-polar liquid shown in Figure 2. Hence, probably the anomalously large contact angle on the \(S\) 70\({}^{1}\) would occur due to the surface polarity which is deeply correlated with the chemical composition of the substrate. The \(S\) 70\({}^{1}\) has a similar F/C ratio with the \(S\) 70\({}^{2}\), but shows a considerable difference in the intensity of the chemical species contained in the XPS spectra.  
Figure 2: Contact angles of five test liquids on various types of substrates.