Graduate Program
Chemistry
Degree Name
Master of Science (MS)
Semester of Degree Completion
2011
Thesis Director
Jon Blitz
Thesis Committee Member
Thomas Over
Thesis Committee Member
Scott MacLaren
Thesis Committee Member
Ted Zobeck
Abstract
Several field and laboratory studies have shown indirectly the effects of atmospheric humidity on soil particle adhesion through reduced resistance to movement by wind as the humidity decreases. Similar studies have also shown that increased hydrophobicity has the same effect on susceptibility of soil particles to movement by wind as reduced humidity. Theoretical models of idealized soil particle cohesion by water menisci in equilibrium with the atmospheric humidity have been used to explain these results. However the interpretation of these phenomenological results has never been tested by direct measurement of soil inter-particle cohesion as a function of humidity and hydrophobicity.
To address this, adhesion force measurements were obtained using an atomic force microscope (AFM) with colloidal glass tips of various sizes to represent one soil particle coming in contact with another. The model surfaces used were Ottawa sand, representing a soil particle with no organic coatings, and a quartz slide representing a more idealized smooth surface. These surfaces were coated with various silanes to mimic fatty acids coating the soil surface, giving the surface induced hydrophobicity.
Hexamethyldisilazane (HMDS) and dichlorodimethylsilane were used to represent shortchained hydrocarbon lipids, and octadecilsilane and palmitic acid were used to represent long-chain hydrocarbon lipids. In addition to these model surfaces, field soil samples were also studied and the results compared to the model surfaces. These force curves were taken at various values of relative humidity in order to measure the combined effect of hydrophobicity and humidity.
The results of these experiments show that with increased relative humidity, there was increased adhesion force between the tip and the surface for most surfaces. At high relative humidity, there was an increase in adhesion force with an increase in tip size and increased surface hydrophobicity. Also, with increased surface roughness (model quartz surface versus model Ottawa sand and field soil samples) there was decreased adhesion force at high relative humidity with the same surface treatments. Also, at high relative humidity on rough surfaces, the measured adhesion force showed a bi-modal distribution showing distinct wet (high adhesion force) and dry (low adhesion force) surfaces. Comparing the data of the model surfaces with that from the field samples showed that, depending on the surrounding foliage, the dichlorodimethylsilane and palmitic acid surface treatments mimicked the relative humidity dependence seen in the field samples in that the soil samples' measured adhesion force usually increased as the relative humidity increased. By using the insights on the cohesive properties of these soils it is possible to improve the prediction of the level of susceptibility of an area to wind erosion.
Recommended Citation
Frost, Bradley Eric, "The affect of surface hydrophobicity on wind erosion probed by atomic force microscopy" (2011). Masters Theses. 931.
https://thekeep.eiu.edu/theses/931
