Gubała Dajana, Fox Laura J, Harniman Robert, Hussain Hadeel, Robles Eric, Chen Meng, Briscoe Wuge H
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK; Bristol Centre for Functional Nanomaterials, HH Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK.
J Colloid Interface Sci. 2021 May 15;590:506-517. doi: 10.1016/j.jcis.2021.01.087. Epub 2021 Feb 2.
Despite the widespread industrial usage of erucamide as a slip additive to modify polymer surface properties, a controversy appears to have persisted regarding the nanostructure of erucamide surface layers, particularly the molecular orientation at the outermost layer. The erucamide nanostructure and molecular orientation, along with its surface coverage, hydrophobicity, and adhesive response, can be tuned by simply varying the erucamide concentration in the solution from which the spin coated layer is prepared.
Synchrotron X-ray reflectivity (XRR) allowed a comprehensive characterisation of the out-of-plane structural parameters (e.g. molecular packing and thickness) of the erucamide layers prepared via spin coating from nonaqueous solution on silica. Complementary Atomic Force Microscopy (AFM) imaging with high lateral resolution revealed localised in-plane structures. Contact angle measurements provided information on the wettability of erucamide-coated surfaces. Peak Force Quantitative Nanomechanical Mapping (QNM) allowed a correlation between the erucamide nanostructure with the surface nanomechanical properties (i.e. adhesive response).
Our results reveal erucamide surface nanostructures on silica as patchy monolayers, isolated circular bilayers/rounded rectangle-like aggregates and overlapping plate-like multilayers as the erucamide concentration in the spin coating solution was varied. In all the cases, XRR and AFM results were consistent with the picture that the erucamide tails were oriented outwards. The QNM adhesion force mapping of all the observed morphologies also supported this molecular orientation at the outermost erucamide monolayer. The wettability study further confirmed this conclusion with the observed increase in the surface hydrophobicity and coverage upon increasing erucamide concentration, with the macroscopic water contact angle θ = 92.9° ± 2.9° at the highest erucamide concentration of 2 wt%.
尽管芥酸酰胺作为一种爽滑添加剂在工业上广泛用于改变聚合物表面性能，但关于芥酸酰胺表面层的纳米结构，尤其是最外层的分子取向，似乎一直存在争议。通过简单改变制备旋涂层所用溶液中的芥酸酰胺浓度，可以调节芥酸酰胺的纳米结构、分子取向及其表面覆盖率、疏水性和粘附响应。
同步加速器X射线反射率（XRR）能够全面表征通过在二氧化硅上从非水溶液旋涂制备的芥酸酰胺层的面外结构参数（如分子堆积和厚度）。具有高横向分辨率的互补原子力显微镜（AFM）成像揭示了局部的面内结构。接触角测量提供了有关芥酸酰胺涂层表面润湿性的信息。峰值力定量纳米力学映射（QNM）使芥酸酰胺纳米结构与表面纳米力学性能（即粘附响应）之间建立了关联。
我们的结果表明，随着旋涂溶液中芥酸酰胺浓度的变化，二氧化硅上的芥酸酰胺表面纳米结构呈现出斑驳的单层、孤立的圆形双层/圆角矩形状聚集体和重叠的板状多层结构。在所有情况下，XRR和AFM结果都与芥酸酰胺尾部向外取向的情况一致。对所有观察到的形态进行的QNM粘附力映射也支持了最外层芥酸酰胺单层的这种分子取向。润湿性研究进一步证实了这一结论，随着芥酸酰胺浓度的增加，表面疏水性和覆盖率增加，在最高芥酸酰胺浓度为2 wt%时，宏观水接触角θ = 92.9°±2.9°。
