Department of Chemical Engineering, §Materials Research Laboratory, and ∥Materials Department, University of California , Santa Barbara, California 93106, United States.
ACS Nano. 2014 Oct 28;8(10):10870-7. doi: 10.1021/nn504687b. Epub 2014 Oct 13.
Strong and particularly long ranged (>100 nm) interaction forces between apposing hydrophobic lipid monolayers are now well understood in terms of a partial turnover of mobile lipid patches, giving rise to a correlated long-range electrostatic attraction. Here we describe similarly strong long-ranged attractive forces between self-assembled monolayers of carboranethiols, with dipole moments aligned either parallel or perpendicular to the surface, and hydrophobic lipid monolayers deposited on mica. We compare the interaction forces measured at very different length scales using atomic force microscope and surface forces apparatus measurements. Both systems gave a long-ranged exponential attraction with a decay length of 2.0 ± 0.2 nm for dipole alignments perpendicular to the surface. The effect of dipole alignment parallel to the surface is larger than for perpendicular dipoles, likely due to greater lateral correlation of in-plane surface dipoles. The magnitudes and range of the measured interaction forces also depend on the surface area of the probe used: At extended surfaces, dipole alignment parallel to the surface leads to a stronger attraction due to electrostatic correlations of freely rotating surface dipoles and charge patches on the apposing surfaces. In contrast, perpendicular dipoles at extended surfaces, where molecular rotation cannot lead to large dipole correlations, do not depend on the scale of the probe used. Our results may be important to a range of scale-dependent interaction phenomena related to solvent/water structuring on dipolar and hydrophobic surfaces at interfaces.
现在，人们已经很好地理解了在相互靠拢的疏水分子单层之间存在着强且具有特殊长程 (>100nm) 的相互作用力，这是通过移动脂质斑块的部分翻转产生相关的长程静电吸引力来实现的。在这里，我们描述了具有相似强度的长程吸引力，存在于咔咯硫醇自组装单层和疏水分子单层之间，这些单层的偶极子平行或垂直于表面排列，并沉积在云母上。我们使用原子力显微镜和表面力仪测量了在非常不同的长度尺度上的相互作用力。这两个系统都给出了长程指数吸引力，对于垂直于表面的偶极子，衰减长度为 2.0±0.2nm。平行于表面的偶极子的作用比垂直偶极子大，这可能是由于平面内表面偶极子的更大的横向相关性。测量的相互作用力的大小和范围也取决于探针的表面积：在扩展表面上，由于自由旋转的表面偶极子和相互靠拢表面上的电荷斑块之间的静电相关性，平行于表面的偶极子导致更强的吸引力。相比之下，在扩展表面上的垂直偶极子，由于分子旋转不能导致大的偶极子相关性，因此不依赖于探针的使用尺度。我们的结果可能对一系列与界面处偶极子和疏水分子表面上溶剂/水结构有关的、具有依赖于尺度的相互作用现象具有重要意义。
