Khan S H, et al. Journal of colloid and interface science, 2016, 473, 93-99.
Nanoscale tetrakis-2-ethylhexyloxysilane (TEHOS) is an inert model liquid with a spherical molecular shape close to 1 nm in diameter. A method based on stiffness and force measurements through a spherical tip on a flat surface is presented to study the Young's modulus of nanoconfined molecular thin layers of model liquids TEHOS and water. Measurements of TEHOS and water indicate large differences in the modulus of these liquids when confined to 3 molecular layers or less. Furthermore, the results show that the elastic modulus of the liquid has little or no dependence on nanoconfinement.
Measurement models and methods
· The elastic modulus (Young's modulus) is a property that represents how much resistance an object offers to being elastically deformed along an axis under the application of a force. The geometry of a hemisphere and a flat surface can be used to model the AFM cantilever tip and a substrate in contact through a liquid film of thickness z.
· Using a homemade atomic force microscope, the vibration of the cantilever beam was monitored using a fiber-optic Fabry-Perot interferometer to measure phase and amplitude.
· Four different cantilevers were used with stiffness values of 55 N/m, 35 N/m, 2.4 N/m and 1.0 N/m. Determine the stiffness of the cantilever using geometric and thermal methods. The radii of the cantilever tips were 19 μm, 6 μm, 0.9 μm, and 0.5 μm, respectively. The substrate used was a polished silicon wafer (100).
