AFM-IR analysis was performed to examine the chemical composition through the fiber cross- section in more detail. Figures 4 and 5 show AFM-IR spectra and AFM images of a cross- section of epoxy-embedded PET round fibers treated with 60 TMA SVI cycles at 150 °C and with 90 TMA SVI cycles at 90 °C, respectively. For both samples, spectra are normalized at 2972 cm–1


at 1268 cm–1


in the high-wavenumber region and in the low-wavenumber region.


Figure 2 – Mass gain of round PET fibers as a function of the number of TMA SVI cycles at temperatures between 60 and 150 °C. TMA cycles were conducted with a sequence of 0.5-second dose/30-second hold/30-second purge followed by H2


In the figures, three spectra were collected from each point shown in the AFM image. Typical absorption peaks for PET are observed at 3436, 2972, 2908, 1720, 1410, 1340, 1268 and 1104 cm–1


. For the SVI fiber treated at 150


°C (Figure 4), absorption intensities at 3436, 2972, 2908 and 1720 cm–1


are attenuated O cycles of approximately


half the number of TMA cycles with a sequence of 0.2-second dose/30-second hold/30-second purge. (Figures 2–5 were adapted from Ref. 1.)


until all the available sites (free volume and reactive sites on the backbone of the polymer) are satisfied. However, the fact that the slope of the line at 60 °C is lower compared to the linear parts of the high-temperature samples suggests slower diffusion rates at lower tem- peratures. As the process temperature is increased, a rapid increase in the mass gain is observed with a corresponding increase in the initial slope. The mass gain saturates quickly, indicating that no precursor is diffused into the samples for subsequent reaction. This decelera- tion of diffusion is a result of the higher reaction kinetics, which forms a dense hybrid layer close to the surface and prevents further penetration of the precursors.


SEM images of pristine and TMA SVI-treated PET fibers are shown in the top half of Figure 3. Cracks have developed as a result of the SVI processing. The bottom half of the figure shows TEM images of cross-sections of the TMA SVI-treated PET fibers obtained at 60 and 150 °C.1


The sample with SVI treatment of 60


°C shows no clear evidence of the formation of a hybrid material, in contrast to the sample exposed at 150 °C, which shows distinct hybrid layer formation.


closer toward the surface, indicating that more of the hybrid material is forming near the surface. The 1020 cm–1


band is likely due to AlOx formation in the fiber as a result of the


SVI processing. The sharp decrease in the C=O stretching peak intensity is coincident with the higher topography in the AFM image and


the denser surface layer observed in the TEM micrographs (Figure 3).


In contrast, the chemical nature near the sur- face of the SVI fiber treated at 90 °C is vastly different. Additional peaks are observed at 2920 and 2860 cm–1 methyl (CH3


, corresponding to the ) stretching vibrations that resulted


from the TMA precursor treatment (Figure 5). These peaks show higher intensity closer to the surface, suggesting that more TMA poly- mer reactions take place closer to the surface. The low-wavenumber region shows peaks at exactly the same wavenumber positions as the sample that was TMA SVI treated at 150 °C. However, all the spectra now show similar band intensities within 1.5 µm of the surface. Since the CH3


peaks and AlOx peak (1020 cm–1 )


are observed, this can be attributed to a more homogeneous composition of the sample within the measured section.


Conclusion Nanoscale AFM-IR spectroscopic depth profil-


ing of the outer portion of surface-modified


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