Water Adsorption Isotherms on CH3-, OH-, and COOH-Terminated Organic Surfaces at Ambient Conditions Measured with PM-RAIRS
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- 作者：Aimee Tu ; Hye Rin Kwag ; Anna L. Barnette ; Seong H. Kim
- 刊名：Langmuir
- 出版年：2012
- 出版时间：October 30, 2012
- 年：2012
- 卷：28
- 期：43
- 页码：15263-15269
- 全文大小：364K
- 年卷期：v.28,no.43(October 30, 2012)
- ISSN：1520-5827
文摘
The water adsorption isotherms on methyl (CH3)-, hydroxyl (OH)-, and carboxylic acid (COOH)-terminated alkylthiol self-assembled monolayers (SAMs) on Au were studied at room temperature and ambient pressure with polarization modulation reflection鈥揳bsorption infrared spectroscopy (PM-RAIRS). PM-RAIRS analysis showed that water does not adsorb at all on the CH3鈥揝AM/Au at subsaturation humidity conditions. In a dry Ar environment, the OH-SAM/Au holds at least 2 layer thick strongly bound water molecules which exhibit a broad O鈥揌 stretch vibration peak centered at 3360 cm鈥?. The peak position implies that the strongly bound water layer on the OH SAM is more like a liquid than an ice. The additional uptake of water in humid environments is relatively weak, and the peak position changes very little. Unlike the OH-SAM/Au, the COOH-SAM/Au does not have strongly bound water layer. This seems to be due to the strong hydrogen bonding between terminal COOH groups in dry conditions. The weak interactions between water and carboxyl groups at low relative humidity (RH) and the solvation of dissociated carboxylic groups in high RH lead to a type III isotherm behavior, based on the BET categories, for water adsorption on the COOH-SAM/Au. The water spectra on the COOH-SAM at RH > 45% are centered at 3430 cm鈥? and very broad, indicating that the hydrogen-bonding network of water on the COOH-SAM is much different from that on the OH-SAM.