Wang Hongfang, Evans Drew, Voelcker Nicolas H, Griesser Hans J, Meagher Laurence
Future Industries Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia.
Future Industries Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia.
J Colloid Interface Sci. 2020 Nov 15;580:690-699. doi: 10.1016/j.jcis.2020.07.035. Epub 2020 Jul 11.
Thin polymeric coatings are commonly used for altering surface properties and modulating the interfacial performance of materials. Possible contributions from the substrate to the interfacial forces and effects are, however, usually ignored and are not well understood, nor is it established how the coating thickness modulates and eventually eliminates contributions from substrates to the van der Waals (vdW) interfacial force. In this study we quantified, by colloid-probe atomic force microscope (AFM) and by theoretical calculations, the interfacial vdW contributions from substrates acting through ethanol plasma polymer (EtOHpp) coatings of a range of thicknesses on Au and Si bulk materials. In approach force curves against EtOHpp-coated Au substrates the magnitude of the vdW force decreased as the EtOHpp coating thickness increased to 18 nm and then plateaued with further increases in coating thickness, providing direct evidence for a contribution to the total interfacial vdW force from the Au substrate acting through thin coatings. The experimental observations accord with theoretical calculations of the thickness dependence of Hamaker coefficients derived from rigorous simulation using the Lifshitz theory. In addition, the measured forces agree well with theoretical predictions including correction for finite roughness. Thus, our experimental and theoretical results establish how the thickness of polymer thin film coatings modulates the total interfacial vdW force and how this can be used to tune the net vdW force so as to either contain a large substrate contribution or arise predominantly from the polymeric overlayer. Our findings enable rational design of coating thickness to tailor interfacial interactions and material performance.
薄聚合物涂层通常用于改变材料的表面性质和调节界面性能。然而，基底对界面力和效应的可能贡献通常被忽略，且未得到很好的理解，涂层厚度如何调节并最终消除基底对范德华（vdW）界面力的贡献也尚未明确。在本研究中，我们通过胶体探针原子力显微镜（AFM）和理论计算，量化了在金和硅块状材料上一系列厚度的乙醇等离子体聚合物（EtOHpp）涂层作用下基底的界面vdW贡献。在与涂有EtOHpp的金基底的接近力曲线中，vdW力的大小随着EtOHpp涂层厚度增加到18纳米而减小，然后随着涂层厚度的进一步增加而趋于平稳，这为通过薄涂层作用的金基底对总界面vdW力的贡献提供了直接证据。实验观察结果与使用 Lifshitz 理论通过严格模拟得出的 Hamaker 系数厚度依赖性的理论计算结果一致。此外，测量的力与包括有限粗糙度校正的理论预测结果吻合良好。因此，我们的实验和理论结果确定了聚合物薄膜涂层的厚度如何调节总界面vdW力，以及如何利用这一点来调整净vdW力，使其要么包含较大的基底贡献，要么主要来自聚合物覆盖层。我们的研究结果有助于合理设计涂层厚度，以定制界面相互作用和材料性能。
