posted on 2015-11-17, 00:00authored byLei Wu, Carlos Ortiz, Ye Xu, Jane Willenbring, Douglas Jerolmack
We present real-time observations
of the diffusion of individual
asbestos fibers in water. We first scaled up a technique for fluorescent
tagging and imaging of chrysotile asbestos fibers and prepared samples
with a distribution of fiber lengths ranging from 1 to 20 μm.
Experiments were then conducted by placing a 20, 100, or 150 ppm solution
of these fibers in a liquid cell mounted on a spinning-disk confocal
microscope. Using automated elliptical-particle detection methods,
we determined the translation and rotation and two-dimensional (2D)
trajectories of thousands of diffusing chrysotile fibers. We find
that fiber diffusion is size-dependent and in reasonable agreement
with theoretical predictions for the Brownian motion of rods. This
agreement is remarkable given that experiments involved non-idealized
particles at environmentally relevant concentrations in a confined
cell, in which particle–particle and particle–wall interactions
might be expected to cause deviations from theory. Experiments also
confirmed that highly elongated chrysotile fibers exhibit anisotropic
diffusion at short time scales, a predicted effect that may have consequences
for aggregate formation and transport of asbestos in confined spaces.
The examined fibers vary greatly in their lengths and were prepared
from natural chrysotile. Our findings thus indicate that the diffusion
rates of a wide range of natural colloidal particles can be predicted
from theory, so long as the particle aspect ratio is properly taken
into account. This is an important first step for understanding aggregate
formation and transport of non-spherical contaminant particles, in
the environment and in vivo.