Micrometer-sized ice particles for planetary-science experiments - I. Preparation, critical rolling friction force, and specific surface energy

TL;DR

This study investigates the physical properties of micrometer-sized water ice particles, including their production methods, surface energy, and adhesion characteristics, which are crucial for understanding planetary ice coagulation processes.

Contribution

It provides the first laboratory measurements of the critical rolling friction force and specific surface energy of micrometer-sized water ice particles, highlighting their stronger adhesion compared to silica particles.

Findings

Ice particles produced with different methods vary in porosity.

Critical rolling friction force of ice exceeds that of silica particles.

Estimated surface energy of ice particles is 0.190 J/m^2.

Abstract

Coagulation models assume a higher sticking threshold for micrometer-sized ice particles than for micrometer-sized silicate particles. However, in contrast to silicates, laboratory investigations of the collision properties of micrometer-sized ice particles (in particular, of the most abundant water ice) have not been conducted yet. Thus, we used two different experimental methods to produce micrometer-sized water ice particles, i. e. by spraying water droplets into liquid nitrogen and by spraying water droplets into a cold nitrogen atmosphere. The mean particle radii of the ice particles produced with these experimental methods are $(1.49 \pm 0.79) \, \mathrm{\mu m}$ and $(1.45 \pm 0.65) \, \mathrm{\mu m}$. Ice aggregates composed of the micrometer-sized ice particles are highly porous (volume filling factor: $\phi = 0.11 \pm 0.01$) or rather compact (volume filling factor: $\phi = 0.72 \pm 0.04$), depending on the method of production. Furthermore, the critical rolling friction force of $F_{Roll,ice}=(114.8 \pm 23.8) \times 10^{-10}\, \mathrm{N}$ was measured for micrometer-sized ice particles, which exceeds the critical rolling friction force of micrometer-sized $\mathrm{SiO_2}$ particles ($F_{Roll,SiO_2}=(12.1 \pm 3.6) \times 10^{-10}\, \mathrm{N}$). This result implies that the adhesive bonding between micrometer-sized ice particles is stronger than the bonding strength between $\mathrm{SiO_2}$ particles. An estimation of the specific surface energy of micrometer-sized ice particles, derived from the measured critical rolling friction forces and the surface energy of micrometer-sized $\mathrm{SiO_2}$ particles, results in $\gamma_{ice} = 0.190 \, \mathrm{J \, m^{-2}}$.