Liascukiene Irma, Steffenhagen Marie, Asadauskas Svajus J, Lambert Jean-François, Landoulsi Jessem
State Research Institute Center for Physical Sciences and Technology, Gostauto 9, Vilnius LT 01108, Lithuania.
Langmuir. 2014 May 27;30(20):5797-807. doi: 10.1021/la404756y. Epub 2014 Feb 27.
The self-assembly of fatty acids (FA) on the surfaces of inorganic materials is a relevant way to control their wetting properties. While the mechanism of adsorption on model flat substrate is well described in the literature, interfacial processes remain poorly documented on nanostructured surfaces. In this study, we report the self-assembly of a variety of FA on a hydroxylated Al surface which exhibits a random nanoscale organization. Our results revealed a peculiar fingerprint due to the FA self-assembly which consists in the formation of aligned nanopatterns in a state of hierarchical nanostructuration, regardless of the molecular structure of the FA (chain length, level of unsaturation). After a significant removal of adsorbed FA using UV/O3 treatment, a complete wetting was reached, and a noticeable disturbance of the surface morphology was observed, evidencing the pivotal role of FA molecules to maintain these nanostructures. The origin of wetting properties was investigated prior to and after conditioning of FA-modified samples taking into account key parameters, namely the surface roughness and its composition. For this purpose, the Wenzel roughness, defined as the third moment of power spectral density, was used, as it is sensitive to high spatial frequency and thus to the obtained hierarchical level of nanostructuration. Our results revealed that no correlation can be made between water contact angles (θ(w)) and the Wenzel roughness. By contrast, θ(w) strongly increased with the amount of -CHx- groups exhibited by adsorbed FA. These findings suggest that the main origin of hydrophobization is the presence of self-assembled molecules and that the surface roughness has only a small contribution to the wettability.
脂肪酸（FA）在无机材料表面的自组装是控制其润湿性的一种重要方式。虽然文献中对其在模型平面基底上的吸附机制已有详尽描述，但在纳米结构表面上的界面过程仍缺乏充分记录。在本研究中，我们报道了多种脂肪酸在具有随机纳米级结构的羟基化铝表面的自组装情况。我们的结果揭示了脂肪酸自组装产生的一种独特特征，即形成了处于分级纳米结构状态的排列纳米图案，这与脂肪酸的分子结构（链长、不饱和度水平）无关。在使用紫外线/臭氧处理显著去除吸附的脂肪酸后，实现了完全润湿，并观察到表面形态有明显扰动，这证明了脂肪酸分子在维持这些纳米结构方面的关键作用。在考虑关键参数（即表面粗糙度及其组成）的情况下，对脂肪酸改性样品处理前后的润湿性来源进行了研究。为此，使用了定义为功率谱密度三阶矩的文泽尔粗糙度，因为它对高空间频率敏感，从而对所获得的纳米结构分级水平敏感。我们的结果表明，水接触角（θ(w)）与文泽尔粗糙度之间不存在相关性。相比之下，θ(w)随吸附的脂肪酸所呈现的 -CHx- 基团数量大幅增加。这些发现表明，疏水化的主要来源是自组装分子的存在，而表面粗糙度对润湿性的贡献较小。
