Influence of Alkyl Chain Length on the Structure of Dialkyldithiophosphinic Acid Self-Assembled Monolayers on Gold

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• 作者：Ronan R. San Juan ; Michael S. Miller ; Michael-Anthony Ferrato ; Tricia Breen Carmichael
• 刊名：Langmuir
• 出版年：2012
• 出版时间：September 18, 2012
• 年：2012
• 卷：28
• 期：37
• 页码：13253-13260
• 全文大小：353K
• 年卷期：v.28,no.37(September 18, 2012)
• ISSN：1520-5827

文摘

We report the formation and characterization of self-assembled monolayers (SAMs) based on dialkyldithiophosphinic acid adsorbates {[CH<sub>3sub>(CH<sub>2sub>)<sub>nsub>]<sub>2sub>P(S)SH (n = 5, 9, 11, 13, 15)} on gold substrates. SAMs were characterized using X-ray photoelectron spectroscopy, reflection鈥揳bsorption infrared spectroscopy, contact angle measurements, and electrochemical impedance spectroscopy. Data show that there is a roughly 60:40 mixture of bidentate and monodentate adsorbates in each of these SAMs. The presence of monodentate adsorbates is due to the numerous and deep grain boundaries of the underlying gold substrate, which disrupt chelation. Comparing the characterization data of dialkyldithiophosphinic acid SAMs with those of analogous n-alkanethiolate SAMs shows that both SAMs follow a similar trend: The alkyl chains become increasingly organized and crystalline with increasing alkyl chain length. The alkyl groups of dialkyldithiophosphinic acid SAMs, however, are generally less densely packed than those of n-alkanethiolate SAMs. For short alkyl chains (hexyl, decyl, and dodecyl), the significantly lower packing densities cause the alkyl chains to be liquid-like and disorganized. Long-chain dialkyldithiophosphinic acid SAMs are only slightly less crystalline than analogous n-alkanethiolate SAMs.