Azadi Mehdi, Nguyen Anh V, Yakubov Gleb E
School of Chemical Engineering and ‡ARC Centre of Excellence in Plant Cell Walls, The University of Queensland , Brisbane, Queensland 4072, Australia.
Langmuir. 2015 Feb 17;31(6):1941-9. doi: 10.1021/la504001z. Epub 2015 Feb 5.
Interfacial gas enrichment of dissolved gases (IGE) has been shown to cover hydrophobic solid surfaces in water. The atomic force microscopy (AFM) data has recently been supported by molecular dynamics simulation. It was demonstrated that IGE is responsible for the unexpected stability and large contact angle of gaseous nanobubbles at the hydrophobic solid-water interface. Here we provide further evidence of the significant effect of IGE on an attractive force between hydrophobic solid surfaces in water. The force in the presence of dissolved gas, i.e., in aerated and nonaerated NaCl solutions (up to 4 M), was measured by the AFM colloidal probe technique. The effect of nanobubble bridging on the attractive force was minimized or eliminated by measuring forces on the first approach of the AFM probe toward the flat hydrophobic surface and by using high salt concentrations to reduce gas solubility. Our results confirm the presence of three types of forces, two of which are long-range attractive forces of capillary bridging origin as caused by either surface nanobubbles or gap-induced cavitation. The third type is a short-range attractive force observed in the absence of interfacial nanobubbles that is attributed to the IGE in the form of a dense gas layer (DGL) at hydrophobic surfaces. Such a force was found to increase with increasing gas saturation and to decrease with decreasing gas solubility.
溶解气体的界面气体富集（IGE）已被证明可覆盖水中的疏水固体表面。原子力显微镜（AFM）数据最近得到了分子动力学模拟的支持。结果表明，IGE是造成气态纳米气泡在疏水固体 - 水界面处具有意外稳定性和大接触角的原因。在此，我们提供了进一步的证据，证明IGE对水中疏水固体表面之间的吸引力有显著影响。通过AFM胶体探针技术测量了溶解气体存在时，即在充气和未充气的NaCl溶液（浓度高达4M）中的力。通过测量AFM探针首次接近平坦疏水表面时的力，并使用高盐浓度来降低气体溶解度，纳米气泡桥接对吸引力的影响被最小化或消除。我们的结果证实存在三种类型的力，其中两种是由表面纳米气泡或间隙诱导空化引起的毛细管桥接起源的长程吸引力。第三种类型是在不存在界面纳米气泡时观察到的短程吸引力，其归因于疏水表面上以致密气体层（DGL）形式存在的IGE。发现这种力随着气体饱和度的增加而增加，随着气体溶解度的降低而降低。
