For thicker layers (sputtering times > 80 s), the CA remains practically constant, reflecting the fact that the post-deposition annealing leads to

the coalescence of the Ag atoms into discrete islands (see Figure 2 and Table 1) and partial uncovering of the PTFE surface. Anomalous drop of contact angle at the initial stage of deposition is probably due to the disposition of silver to react with oxygen from ambient atmosphere (see, e.g., [20]). This phenomenon is particularly pronounced in tiny Ag structures [21]. Oxygen-rich compounds increase the sample wettability (see also Table 1; Ag/O ratio becomes lower for thin annealed layers). Figure 2 AFM images. AFM images of pristine and Ag-coated PTFE (20, 100, and 200 s) for relaxed and annealed samples.

Table RO4929097 nmr 1 XPS elemental analysis of the Ag/PTFE composites C188-9 Samples Sputtering time (s) Elemental composition (at.%) Ag O F C As-sputtered 20 11.7 2.8 37.3 48.2   100 28.7 8.5 7.9 54.8   200 29.9 15.3 – 54.8 Relaxed 20 11.0 6.6 30.1 52.3   100 23.6 6.0 21.1 49.3   200 25.0 10.2 2.0 62.8 Annealed 20 – - 66.0 34.0   100 2.5 0.9 57.7 39.0   200 4.4 0.7 59.6 35.3 UV–vis spectroscopy UV–vis absorption spectra of relaxed (A) and annealed (B) samples are shown in Figure 3. As expected, the absorbance increases with increasing deposition time as the Ag layer becomes thicker. The spectra of the annealed samples exhibit distinctive narrow absorption peak at about 400 nm, click here corresponding pheromone to the surface plasmon resonance (SPR) in silver nanostructures. It is well known that the position and shape of the SPR peak is closely related to the nanostructure shape and to the surrounding medium [22, 23]. The appearance

of absorption peak after annealing indicates the formation of discontinuous Ag clusters of hummock-like shape (see Figure 2) homogeneously distributed over the PTFE surface [24]. The absorption band corresponding to the bounded plasma resonance in the metal nanostructures is slightly shifted to longer wavelengths when the cluster density increases. Moreover, as the silver layer becomes thicker, the absorption band broadens due to wider distribution of the cluster size. The spectra of the as-deposited samples (Figure 3A) with deposition times below 30 s possess only weak SPR peak. In this case, the SPR peak is widespread and hardly identifiable because of insufficient separation of fundamental building blocks (clusters) of silver layer in the initial stage of the layer growth, where the formation of discontinuous but interconnected Ag coating is expected [19]. Figure 3 UV–vis absorption spectra of silver-coated PTFE. Relaxed (A) and annealed (B) samples sputtered for different times. Chemical composition Besides the wettability, the chemical composition of the sample surface plays essential role in material biocompatibility [25, 26]. Moreover, the elemental composition is closely linked to the wettability.