Creating Long-Lived Superhydrophobic Polymer Surfaces Through Mechanically Assembled Monolayers Jan Genzer and Kirill Efimenko

Supplementary Material

The NEXAFS experiments were carried out on the U7A NIST/Dow materials characterization end-station at the National Synchrotron Light Source at Brookhaven National Laboratory (1). Web fig. 1 shows the partial electron yield (PEY) NEXAFS spectra collected from F8H2-MAM samples with Dx = 0% (Fig. 2A in the paper), and Dx = 70% (Fig. 2B in the paper). PEY NEXAFS spectra taken in the direction parallel (upper spectra) and perpendicular (lower spectra) to the stretching direction are shown for both samples. In all cases the PEY NEXAFS spectra were collected at the normal (q = 90°) and grazing (q = 20°) incidence geometries, where q is the angle between the sample normal and the polarization vector of the x-ray beam. By inspecting the PEY NEXAFS signals shown in Web fig. 1, several characteristic peaks can be identified that correspond to the 1s s* transitions associated with the C-H (E = 287.0 eV), C-F (E = 292.0 eV), and C-C (E = 295.5 eV) bonds. The fact that the intensities originating from these transitions change with varying angle q (as q increases the intensity corresponding to s* of the C-F bond increases while that of the C-C bond decreases) indicates that the samples are oriented. The orientation of the F8H2 molecules can be inferred by qualitatively examining the PEY NEXAFS data. The s*C-F signal in the NEXAFS spectra collected at q = 90° is always stronger than that measured at q = 20°; thus the director of the F8H2 molecule is only slightly tilted away from the sample normal.

References

1. The principles of NEXAFS (2) and description of the BNL beamline (3) have been presented elsewhere. The NIST/Dow materials characterization end-station is equipped with a sample holder positioned on a goniometer, which controls the orientation of the sample with respect to the polarization vector of the x-rays. The partial-electron-yield (PEY) signal is collected using a channeltron electron multiplier with an adjustable entrance grid bias. A differentially pumped ultra-high vacuum compatible proportional counter is used for collecting the fluorescence yield (FY) signal. The monochromator energy resolution and photon energy were calibrated by comparing the transmission spectrum from gas-phase carbon monoxide with electron energy-loss reference data. To eliminate the effect of incident beam intensity fluctuations and monochromator absorption features, the NEXAS signal was normalized by the incident beam intensity obtained from the photo yield of a clean gold grid.

2. J. Stöhr, NEXAFS Spectroscopy, (Springer-Verlag: Berlin, 1992).

3. D. A. Fischer et al., Appl. Surf. Sci. 133, 58 (1998).

Supplemental Figure 1. The partial electron yield (PEY) NEXAFS spectra at the C edge of F8H2-MAMs deposited on PDMS-UVO substrates that were not stretched (A) and stretched to Dx = 70% (B) before the UVO treatment. The solid and dotted lines denote the PEY NEXAFS spectra taken at the normal (q = 90°) and grazing (q = 20°) incidence, respectively, geometries of the X-ray beam along (upper spectra) and perpendicular to (lower spectra) the stretching direction. The arrows indicate the positions of the 1s s* transitions associated with the C-H (E = 287.0 eV), C-F (E = 292.0 eV), and C-C (E = 295.5 eV) bonds. The inset shows schematically the set-up geometry.

Medium version | Full size version