es050386j_si_001.pdf (216.09 kB)
Characterization of Freshwater Natural Aquatic Colloids by Atomic Force Microscopy (AFM)
journal contribution
posted on 2005-09-15, 00:00 authored by J. R. Lead, D. Muirhead, C. T. GibsonAtomic force microscopy (AFM) has been used to image
and quantify riverine colloids in a quantitative and relatively
nonperturbing manner. Three main classes of material
have been imaged including fibrils (about 10 nm in diameter
and 100 nm or more in length), discrete, near-spherical,
small colloids primarily below 30−50 nm in diameter, and
a surface film, of at least several nanometers thickness,
which coats the entire mica surface within 30 min of exposure
to river water. Colloid structure was found to vary as a
function of pH, particularly at high pH. Substantially different
structures were observed at high pH values, with the
loss of the near-spherical colloids possibly due to
rearrangement and aggregation. In addition, film thicknesses
of up to 100 nm were estimated on the silicon nitride
AFM cantilever after 30 h of deposition in the same water
(unperturbed and size fractionated). The observation of
these surface films has important implications for
understanding the mechanisms by which colloids might
bind trace elements. In particular, development of surface
coatings implies that binding of pollutants (at least initial
surface binding) may be dominated by adsorbed surface
layers.