Malham Ibrahim B, Bureau Lionel
Institut des Nanosciences de Paris, UMR 7588 CNRS-Universites Paris 6 and 7, 140 rue de Lourmel, 75015 Paris, France.
Langmuir. 2009 May 19;25(10):5631-6. doi: 10.1021/la804213q.
Increasing the range of surfaces that can be studied using the surface forces apparatus, e.g., for friction measurements, requires chemical modification of the surface of mica, which may be achieved by grafting self-assembled monolayers (SAMs) onto plasma-modified mica. In order to gain a better idea of the grafting conditions leading to good-quality SAMs on plasma-activated mica, we focus, in the present work, on the early stages of octadecyltriethoxysilane (OTE) deposition. We use atomic force microscopy to study the morphologies of incomplete monolayers obtained at different grafting temperatures in the range 10-30 degrees C, and for different immersion times in dilute solutions of OTE. We observe that OTE molecules deposited on plasma-treated mica form stable and robust layers, the morphology of which are markedly affected by the grafting temperature: submonolayers deposited at temperatures below 18 degrees C exhibit micrometer-sized islands of well-packed molecules, whereas much smaller ordered domains, coexisting with a "liquid-expanded" phase, are observed at room temperature and above. We use water contact angle measurements to probe the quality of the SAMs, and find in particular that the most hydrophobic SAMs, presenting large contact angles and low hysteresis, are obtained for deposition temperature below 18 degrees C.
扩大使用表面力仪可研究的表面范围，例如用于摩擦测量，需要对云母表面进行化学改性，这可通过将自组装单分子层（SAMs）接枝到等离子体改性的云母上来实现。为了更好地了解在等离子体活化的云母上形成高质量SAMs的接枝条件，在本工作中，我们聚焦于十八烷基三乙氧基硅烷（OTE）沉积的早期阶段。我们使用原子力显微镜研究在10 - 30摄氏度范围内不同接枝温度以及在OTE稀溶液中不同浸泡时间下获得的不完全单分子层的形态。我们观察到，沉积在等离子体处理云母上的OTE分子形成稳定且坚固的层，其形态受接枝温度的显著影响：在低于18摄氏度时沉积的亚单分子层呈现出微米级大小的排列紧密分子的岛状结构，而在室温及以上温度时观察到的有序域要小得多，且与“液体扩展”相共存。我们用水接触角测量来探测SAMs的质量，特别发现对于沉积温度低于18摄氏度时获得的SAMs，其疏水性最强，具有大接触角和低滞后现象。
