Structure and reactivity of mixed omega-carboxyalkyl/alkyl monolayers on silicon: ATR-FTIR spectroscopy and contact angle titration.
Structure and reactivity of mixed omega-carboxyalkyl/alkyl monolayers on silicon: ATR-FTIR spectroscopy and contact angle titration.
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DOI：
10.1021/la035813q
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发表时间：
2004-04
期刊：
影响因子：
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通讯作者：
Yong-Jun Liu;Neenah Navasero;Hua-Zhong Yu
中科院分区：
文献类型：
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作者：
Yong-Jun Liu;Neenah Navasero;Hua-Zhong Yu
通过ATR-FTIR光谱和接触角测量，研究了端氢硅与十一烯酸乙酯和正烯的混合物光化学反应制备的混合单层膜的结构、反应性和酸碱性质。通过系统地改变十一烯酸乙酯的摩尔分数和未取代烯烃的链长，研究了混合单层膜的表面组成及其与末端乙氧羰基（酯）基水解反应活性的关系。结果表明，表面酯基的摩尔分数与溶液中十一烷基酸乙酯的摩尔分数相差不大。酸条件下酯的水解效率受到单层结构的显著影响，即酯基的表面密度和未取代烷基链的长度。此外，我们发现在硅上（通过水解制备）的混合omega-烷酸/烷基单层具有明确的接触角滴定曲线，由此可以确定表面酸解离常数。结果与文献报道的羟基化硅上羧酸端烷基硅氧烷单层和金上-巯基烷酸/烷硫酸酯单层的酸碱性质进行了比较。pKa对羧基表面密度和未取代烷基链长度的依赖性较弱（δ ka约为1），主要归因于酸基微环境的变化。这些实验结果为在晶体半导体衬底上制备可控反应性的生物反应表面提供了分子水平上的基础知识。
The structure, reactivity, and acid-base properties of mixed monolayers prepared by photochemical reaction of hydrogen-terminated silicon with mixtures of ethyl undecylenate and n-alkenes were studied by ATR-FTIR spectroscopy and contact-angle measurements. The surface composition of the mixed monolayers and its correlation with the hydrolysis reactivity of terminal ethoxycarbonyl (ester) groups were investigated by systematically varying the mole fraction of ethyl undecylenate and the chain length of the unsubstituted alkenes in the binary deposition solution. It has been shown that the mole fraction of ester groups on the surface deviates only slightly from the mole fraction of ethyl undecylenate in the solution. The efficiency of ester hydrolysis under acidic conditions is significantly influenced by the monolayer structure, i.e., the surface density of ester groups and length of the unsubstituted alkyl chains. In addition, we find that mixed omega-alkanoic acid/alkyl monolayers on silicon (prepared via hydrolysis) exhibit well-defined contact angle titration curves from which the surface acid dissociation constants were determined. The results were compared with the acid-base properties reported in the literature for carboxylic acid-terminated alkylsiloxane monolayers on hydroxylated silicon and for omega-mercaptoalkanoic acid/alkanethiolate monolayers on gold. The weak pKa dependence (deltapKa approximately 1) on the surface density of carboxylic acid groups and on the length of unsubstituted alkyl chains is attributed to variations of the microenvironment of the acid moieties. These experimental findings provide fundamental knowledge at the molecular level for the preparation of bioreactive surfaces of controlled reactivity on crystalline semiconductor substrates.