Micro-mechanical Force Apparatus

The micromechanical force apparatus was designed by Dr. K.T. Miller in 2002, and brought over to the laboratory from the Colorado School of Mines Material Science department in 2004. The micromechanical testing apparatus was developed to measure the adhesive forces acting between hydrate particles submerged in a cooled liquid. A picture of the apparatus is shown in Figure 1. An inverted light microscope (Carl Zeiss Axiovert S100) is positioned on a vibration isolation table. A cooling cell is attached to the microscope stage, in which hydrates are submerged in a cooled liquid. Two micromanipulators are connected to the microscope to control the movement of the hydrate particles. One manipulator is a relatively low precision hand-operated micromanipulator (Narishige MN-151) which is held stationary during the experiment. A second, high precision remote-operated micromanipulator (Eppendorf Patchman 5173) is used to move one of the hydrate particles.

Figure 1: Picture of micromechanical apparatus

Digital video microscopy was used to track the movement of particles attached to low spring constant cantilever beams, as the beams were displaced with the moving micromanipulator. The cantilever beams are made of thin glass fibers (~ 30 µm diameter) and are attached to the inside of the capillary tubes by epoxy cement. The capillary tubes were held in place by cantilever holders attached to the micromanipulators. The micromechanical force measurement technique is illustrated schematically in the Figure 2. Hydrate particles were formed on the end of thin glass fiber cantilever beams, which act as springs. Using the micromanipulators, the hydrate particles are brought into contact (A). Using the remote operated manipulator, a preload contact force of ~ 10 µN was applied to the hydrates particles and held stationary for multiple seconds (Figure 2B). The particles were then gently pulled apart from each other using the remote operated manipulator. While the particles were being pulled apart, the stationary cantilever bends due to the particle-particle adhesion (Figure 2C). At some critical displacement, the adhesive bond between the particles breaks, and the particles separate (Figure 2D). This displacement, of the particles, was tracked using digital video microscopy and image analysis. For each adhesion force measurement, the particles were pulled apart 40 times to obtain a range of forces.

Figure 2. Schematic of micromechanical technique.
(A) Resting position. (B) Initial preload. (C) Maximum displacement immediately prior to pulloff. (D) Equilibrium cantilever position after hydrates separated.

Figure 3. A typical adhesion experiment.
(A) Resting position. (B) Initial preload. (C) Maximum displacement immediately prior to pulloff. (D) Equilibrium cantilever position after particles separated.