Wettabilities of self-assembled monolayers on gold generated from progressively fluorinated alkanethiols
Wettabilities of self-assembled monolayers on gold generated from progressively fluorinated alkanethiols
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DOI：
10.1021/la0263763
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发表时间：
2003-04-15
期刊：
影响因子：
3.9
通讯作者：
Lee, TR
中科院分区：
文献类型：
--
作者：
Colorado, R;Lee, TR
研究了一系列部分氟化烷基硫醇（F（CF 2）（n）（CH 2）（11）SH，n = 1- 10; FnH 11 SH，H11系列），具有相等长度的亚甲基间隔基，采用偏振调制红外反射吸收光谱法对正烷基硫醇（F0 H11 SH）进行了表征（PM-IRRAS）和接触角测角法。PM-IRRAS分析显示，随着n的增加，潜在亚甲基间隔区的构象顺序保持不变。通过使用烃和碳氟化合物接触液体的接触角测角法探测自组装膜的润湿性，发现单层的分散表面能随着n从0增加到6而减小，然后在n = 6-10时保持恒定。使用顺式全氟萘烷作为接触液体表明，分散表面能的降低是由于CF 3基团表面密度的降低，这种降低是由于全氟碳链段的长度随着n的增加而增加而发生的。烃类液体的接触角揭示了底层CF2基团的存在可以进一步降低表面处的分散相互作用的强度。极性接触液体的自组装膜上的接触角是一致的，随着n的增加，从单层表面的定向氟碳烃（FC-HC）偶极子的距离增加。粘附功的计算支持了这一模型。对衍生自H11系列的SAM测量的数据与对衍生自总链长保持恒定的一系列部分氟化的烷硫醇的SAM测量的数据的比较（FnHmSH; n = 1-10，m = 15-6; n + m = 16; C16系列）和相应的正烷基硫醇（F0 H15 SH）揭示了底层单层结构的差异不能显著影响所有接触液体的界面润湿性。使用Zisman和Good、吉里法尔科和Fowkes（GGF）的方法计算SAM的分散表面能表明，当使用烃接触液体时，两种方法都低估了氟碳化合物表面的能量，与在GGF方法中使用氟碳化合物接触液体估计的能量相比，Zisman的方法提供了更低的估计。总体而言，结果表明，用碳氟链段（n大于或等于6）取代烷乙氧基SAM中的末端烃链段产生具有对下面的膜结构不太敏感的润湿性的较低能量表面。
The conformational order and wettability of self-assembled monolayers (SAMs) on gold generated from a series of partially fluorinated alkanethiols (F(CF2)(n)(CH2)(11)SH, n = 1- 10; FnH11SH, H11 series), possessing methylene spacers of equivalent length, and the corresponding n-alkanethiol (F0H11SH) were characterized by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and contact angle goniometry. The PM-IRRAS analyses revealed that the conformational order of the underlying methylene spacers remains constant with increasing n. Probing the wettabilities of the SAMs by contact angle goniometry using hydrocarbon and fluorocarbon contacting liquids revealed that the dispersive surface energies of the monolayers decreased as n increased from 0 to 6 and then remained constant for n = 6-10. Using cis-perfluorodecalin as the contacting liquid revealed that the decrease in the dispersive surface energies is due to a decrease in the surface density of the CF3 groups that occurs as the length of the perfluorocarbon segment increases with increasing n. The contact angles of the hydrocarbon liquids revealed that the presence of underlying CF2 groups can further reduce the strength of the dispersive interactions at the surface. The contact angles of polar contacting liquids on the SAMs were consistent with an increase in the distance of the oriented fluorocarbon-hydrocarbon (FC-HC) dipoles from the monolayer surface with increasing n. Calculation of the works of adhesion supported this model. Comparison of the data measured for SAMs derived from the H11 series to those measured for SAMs derived from a series of partially fluorinated alkanethiols whose total chain lengths were held constant (FnHmSH; n = 1-10, m = 15-6, respectively; n + m = 16; C16 series) and the corresponding n-alkanethiol (F0H15SH) revealed that differences in underlying monolayer structure fail to significantly influence the interfacial wettabilities of all of the contacting liquids. Calculation of the dispersive surface energies of the SAMs using the methods of both Zisman and Good, Girifalco, and Fowkes (GGF) revealed that both methods underestimate the energies of fluorocarbon surfaces when hydrocarbon contacting liquids are used, with Zisman's method providing lower estimates, compared to the energies estimated using a fluorocarbon contacting liquid in the GGF method. Overall, the results demonstrate that substituting fluorocarbon segments (n greater than or equal to 6) for the terminal hydrocarbon segments in alkanethiol SAMs produces lower energy surfaces having wettabilities that are less sensitive to the underlying film structure.