Effects of hydrophobic and hydrophilic organic matter on the water repellency of model sandy soils

Abstract

Soil water repellency affects the hydrological functions of soil systems. Water repellency is associated with the content and the composition of soil organic matter. In the present study, we examined the effects of hydrophobic and hydrophilic organic matter contents, the hydrophobic ⁄ hydrophilic organic matter ratio and the total organic matter content on water repellency using model sandy soils. Stearic acid and guar gum were used as the hydrophobic and hydrophilic organic compounds, respectively. Water repellency was estimated using the sessile drop method. Hydrophobic organic matter content was found to be the dominant factor affecting soil water repellency. Hydrophilic organic matter was found to increase the contact angle to some extent without the presence of hydrophobic organic matter. With the presence of both hydrophobic and hydrophilic organic matter, the effects of the hydrophilic organic matter content on contact angle were found to be dependent on the hydrophobic organic matter content of the soil. This relationship was explained by the differences in the surface free energies of different organic matter and mineral surfaces. The contact angle increased with increasing hydrophobic ⁄ hydrophilic organic matter ratio when the hydrophilic organic matter content was constant. When the hydrophobic organic matter content was constant, contact angles were roughly comparable, irrespective of the hydrophobic ⁄ hydrophilic organic matter ratio. The contact angles were not comparable at each total organic matter content. Accordingly, the hydrophobic ⁄ hydrophilic organic matter ratio and the total organic matter content in soil may not provide satisfactory information about soil water repellency.

Coating Sand with New Hydrophobic and Superhydrophobic Silica/Paraffin Wax Nanocapsules for Desert Water Storage and Transportation

“…Silica nanomaterials and silicon derivatives have gained immense attention for the development of superhydrophobic sand because of their excellent adhesion with sand and glass surfaces [18][19][20][21][22][23]. Organic silicone derivatives, such as octadecyltrichlorosilane have also been used for coating sand to produce hydrophobic sand [24].…”

Assay of Soil Water Repellency of Coastal Forest Catchment in Subtropical Okinawa Island of Japan

“…SWR is a phenomenon that reduces the affinity of soil to water (Doerr et al, 2000) or inability of soil to get wet spontaneously when water is added (Leelamanie et al, 2008a) due to the higher cohesive forces than the adhesive forces (Doerr et al, 2000). Though mineral particles have high surface free energy than water, due to the presence of hydrophobic materials, wettability declines (Doerr et al, 2000;Leelamanie and Karube, 2009a). Usually organic matter acts as hydrophobic material (Mataix-Solera et al, 2007).…”

New approaches to the study of hydrophobicity and wetting of soils: methods and theories

“…Stearic acid has been extensively used in many water repellency studies on model soils (Leelamanie et al, 2008;2007, 2009Leelamanie et al, 2010;Leelamanie et al, 2012;Mainwaring et al, 2013;Whelan et al, 2015). Yiannos (1962) noted that upon contact with water it was possible for the stearic acid molecule to reorientate itself and therefore alter the water repellency level of the soil, this has been confirmed by other researchers since, Leelamanie and Karube (2009) and Whelan et al (2015).…”

“…McIntosh and Horne (1994) identified aliphatic hydrocarbons and amphiphilic compounds as being most important in inducing soil hydrophobicity. Leelamanie and Karube (2009) suggested that it is specifically the hydrophobic organic matter content of soils that is the dominant factor in influencing soil water repellency, rather than the total organic matter content. Mainwaring et al (2013) found that the extent of water repellency induced on acid-washed sand varied considerably with compound type and laydown, with a combination of long chain acids and alkanes to be most effective at inducing water repellency.…”