Multiple Transmission−Reflection Infrared (MTR-IR) Spectroscopy of Arachidic Acid LB Films on Hydrophilic and Hydrophobic Silicon Surfaces
journal contributionposted on 14.01.2010, 00:00 by Peng-Feng Guo, Hong-Bo Liu, Xiang Liu, Hong-Fang Li, Wen-Yi Huang, Shou-Jun Xiao
Our recently developed multiple transmission−reflection infrared (MTR-IR) spectroscopy method was applied to measure arachidic acid Langmuir−Blodgett films on hydrophilic and hydrophobic silicon substrates. High-quality MTR-IR spectra at both s and p polarizations were obtained. The MTR-IR absorption intensity at different incident angles was found to be linearly correlated with the transmission times (N) for arachidic acid monolayers on a hydrophilic silicon substrate. Significant differences in polarization-dependent intensities were observed for some specific vibration modes, for example, CH3 and CH2 stretching, carboxylic acid stretching, and CH2 bending, on different types of monolayer and multilayer films. By means of polarization-dependent spectra, the molecular orientation was numerically calculated, and the molecular structures such as the crystalline packing of hydrocarbon chains and the trans and cis configurations of carboxylic acid species were deduced. Obvious and repeatable intensity differences for the same vibration mode from s to p polarization strongly confirmed the stability and credibility of our MTR-IR method.