Measurement of the surface hydrophobicity of engineered nanoparticles using an atomic force microscope
Measurement of the surface hydrophobicity of engineered nanoparticles using an atomic force microscope
复制标题
DOI：
10.1039/c8cp04676j
复制
发表时间：
2018-10-07
影响因子：
3.3
通讯作者：
Zhang, Wen
中科院分区：
文献类型：
--
作者：
Fu, Wanyi;Zhang, Wen
纳米材料和纳米颗粒（NP）的表面疏水性或润湿性的测定通常受到NP的异质性的挑战，所述异质性随颗粒尺寸、形状、表面电荷、聚集状态和表面吸附或涂覆而变化。本研究首先总结了水接触角、正辛醇-水分配系数（K-ow）和探针分子表面吸附在探测纳米材料疏水性方面的固有局限性。然后，我们展示了基于原子力显微镜（AFM）的扫描探针方法的局部表面疏水性测量的原理。具体而言，我们测量了功能化的AFM针尖和自组装单分子膜（SAMs）之间的粘附力，建立了基于连续热力学方法（CTA）的粘附力和水接触角之间的线性关系。该关系用于确定七种不同NP的局部表面疏水性（即，TiO2、ZnO、SiO2、CuO、CeO2、α-Fe2O3和Ag），这与这些NP的体接触角很好地一致。观察到Fe2O3，CeO2和SiO2纳米颗粒的一些差异，可能是因为表面水合和粗糙度的影响。此外，溶液pH和离子强度对AFM针尖与碳纳米管或C-60之间的粘附力影响很小，表明碳纳米材料的疏水性不受pH或离子强度（IS）的影响。相比之下，天然有机物（NOM）明显降低了多壁碳纳米管和C-60的疏水性，由于亲水NOM的表面涂层。这种扫描探针方法已被证明是可靠的和鲁棒性的准确测量的纳米级疏水性的单个纳米颗粒或纳米材料在液体环境中。
Determination of the surface hydrophobicity or wettability of nanomaterials and nanoparticles (NPs) is often challenged by the heterogeneous properties of NPs that vary with particle size, shape, surface charge, aggregation states, and surface sorption or coating. This study first summarized inherent limitations of the water contact angle, octanol-water partition coefficient (K-ow) and surface adsorption of probe molecules in probing nanomaterial hydrophobicity. Then, we demonstrated the principle of a scanning probe method based on atomic force microscopy (AFM) for the local surface hydrophobicity measurement. Specifically, we measured the adhesion forces between functionalized AFM tips and self-assembled monolayers (SAMs) to establish a linear relationship between the adhesion forces and water contact angles based on the continuum thermodynamic approach (CTA). This relationship was used to determine the local surface hydrophobicity of seven different NPs (i.e., TiO2, ZnO, SiO2, CuO, CeO2, alpha-Fe2O3, and Ag), which agreed well with bulk contact angles of these NPs. Some discrepancies were observed for Fe2O3, CeO2 and SiO2 NPs, probably because of surface hydration and roughness effects. Moreover, the solution pH and ionic strength had negligible effects on the adhesion forces between the AFM tip and MWCNTs or C-60, indicating that the hydrophobicity of carbonaceous nanomaterials is not influenced by pH or ionic strength (IS). By contrast, natural organic matter (NOM) appreciably decreased the hydrophobicity of MWCNTs and C-60 due to surface coating of hydrophilic NOM. This scanning probe method has been proved to be reliable and robust toward the accurate measurement of the nanoscale hydrophobicity of individual NPs or nanomaterials in liquid environments.