Absolute Orientation of Ester Side Chains on the PMMA Surface

作者：Jena Kailash C; Covert Paul A; Hall Shaun A; Hore Dennis K^*

来源：Journal of Physical Chemistry C, 2011, 115(31): 15570-15574.

DOI：10.1021/jp205712c

Phase-resolved sum-frequency generation spectroscopy has been used to measure the complex, nonlinear susceptibility spectra of the ester methyl groups at the poly(methyl methacrylate) air interface. The response of the ester methyl symmetric stretch is found to be in phase with that of the aliphatic methyl symmetric stretch in an ordered octadecylsilane monolayer. However, because the local bonding environments of these two methyl groups differ significantly, the signs of the molecular hyperpolarizability tensor elements are not necessarily the same. Therefore, the ester methyl orientation cannot be inferred from the phase measurements alone. To address this ambiguity, the relevant tensor elements were calculated for both types of methyl groups. Results of these calculations, combined with spectroscopic evidence, indicate that the ester methyl groups at the polymer surface are oriented with their hydrogen atoms directed toward the air. This finding may be used to better understand the hydrophobicity and reactivity of the polymer surface.

• 出版日期2011-8-11