Abstract
We study the size dependence of pull-off forces of water ice in laboratory experiments and numerical simulations. To determine the pull-off force in our laboratory experiments, we use a liquid nitrogen cooled centrifuge. Depending on its rotation frequency, spherical ice grains detach due to the centrifugal force which is related to the adhesive properties. Numerical simulations are conducted by means of molecular dynamics simulations of hexagonal ice using a standard coarse-grained water potential. The pull-off force of a single contact between two spherical ice grains is measured due to strain controlled simulations. Both, the experimental study and the simulations reveal a dependence between the pull-off force and the (reduced) particle radii, which differ significantly from the linear dependence of common contact theories.
Highlights
In a standard scenario of planet formation, collisions between particles and aggregates thereof are important [1, 2]
Due to the fact that the sticky spherical water ice particles were removed in the tangential direction from the surface of the ice flywheel, this process is linked to a critical torque MC = R · Fcf, where R = Rred is the radius of a certain spherical particle
Before the actual strain controlled simulations and the calculation of FC are explained, we describe how the system evolves during its relaxation
Summary
In a standard scenario of planet formation, collisions between particles and aggregates thereof are important [1, 2]. The interaction between these particles is fundamental for e.g. the formation of comets. Whether ice aggregates grow in mutual collisions depends on their sticking properties. It is commonly assumed [2], that ice aggregates can grow, if the kinetic collision ECcoll energy does not exceed. Δc is a critical displacement and FC is the pull-off force needed to separate two particles. To understand the early process of planet formation, it is crucial to know the pull-off force FC.
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