Surface and Frictional Properties of Two-Component Alkylsilane Monolayers and Hydroxyl-Terminated Monolayers on Silicon
Surface and Frictional Properties of Two-Component Alkylsilane Monolayers and Hydroxyl-Terminated Monolayers on Silicon
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DOI：
10.1021/jp904809h
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发表时间：
2009-07
影响因子：
3.7
通讯作者：
Steven G. Vilt;Ziwei Leng;Brandon D. Booth;C. McCabe;G. Jennings
中科院分区：
文献类型：
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作者：
Steven G. Vilt;Ziwei Leng;Brandon D. Booth;C. McCabe;G. Jennings
为了研究链迁移率和官能团暴露对摩擦的影响，提出了硅上单组分（纯）和双组分（混合）烷基硅烷单层的摩擦学特性，以及长链和短链分子比例的变化。这些单层的摩擦学特性是用平球摩擦仪在 9.8 mN 负载和 0.1 mm/s 速度下测量的。研究的分子前体是正己基三氯硅烷 (C6)、正十二烷基三氯硅烷 (C12)、正十六烷基三氯硅烷 (C16)、正十八烷基三氯硅烷 (C18) 和正二十二烷基三氯硅烷 (C22)。由这些分子创建了以下四种混合单层：C6/C18、C12/C18、C16/C18 和 C12/C22，其中长链分子和短链分子的比例不同，以便在薄膜的上部液体区域中产生不同水平的迁移率和平均链倾斜。对于双组分单层膜，一旦达到临界厚度，尽管混合膜的亲油性要高得多，但摩擦学性能与纯单层膜没有区别。然而，将单层的末端基团改变为羟基会导致单层与微摩擦计的不锈钢探针之间的摩擦系数增加和显着的粘附力。这种摩擦学行为可以用甲基和亚甲基的低表面能以及羟基封端单层由于更强的界面相互作用而增加的粘附力来解释。总的来说，结果表明单层厚度和表面能极大地影响单层的摩擦学性能，但在这些负载和速度下，薄膜内的分子迁移率和界面亲油性不太重要。
To investigate the effect of chain mobility and functional group exposure on friction, the tribological properties of one-component (pure) and two-component (mixed) alkylsilane monolayers on silicon, with variance in the ratios of long- and short-chain molecules, are presented. The tribological properties of these monolayers were measured with a ball-on-flat tribometer at 9.8 mN load and a speed of 0.1 mm/s. The molecular precursors investigated were n-hexyltrichlorosilane (C6), n-dodecyltrichlorosilane (C12), n-hexadecyltrichlorosilane (C16), n-octadecyltrichlorosilane (C18), and n-docosyltrichlorosilane (C22). Created from these molecules were the following four mixed monolayers: C6/C18, C12/C18, C16/C18, and C12/C22 in which the ratio of long- and short-chain molecules was varied in order to create different levels of mobility and average chain cant in the upper liquidlike region of the film. For the two-component monolayers, once a critical thickness is reached, the tribological properties were indistinguishable from the pure monolayers although the oleophilicity was much higher for the mixed films. Altering the terminal group of the monolayer to a hydroxyl, however, resulted in an increased coefficient of friction and significant adhesive forces between the monolayer and the stainless steel probe of the microtribometer. This tribological behavior can be explained by the low surface energies of the methyl and methylene groups and the increased adhesion that occurs with hydroxyl-terminated monolayers due to stronger interfacial interactions. Collectively, the results indicate that monolayer thickness and surface energy greatly affect the tribological properties of a monolayer but that molecular mobility within the film and interfacial oleophilicity are less important at these loads and speeds.