Effects of amphiphilic amines on moisture characteristics of alluvial and volcanic soils
2001
Suetsugu, A. | Miyazaki, T. | Nakano, M.
If organic matter (OM) has amphiphilicity, the properties of hydration of the OM-coated soil particles would vary drastically in dry conditions. Therefore, soil-moisture characteristics within the relatively low water potential should be understood in relation to the conformation of the sorbed amphiphilic OM. In the present study, the effects of amphiphilic behavior of OM on the moisture characteristics of alluvial soil (AS) and volcanic soil (VS) were investigated using three simple amphiphilic amines. The psychrometry of AS showed the decrease of sorbed water around 1.8 nm of statistical thickness because of the sorption of hexadecyltrimethyl ammonium (HDTMA). Fourier transform infrared spectroscopy (FTIR) of soils showed an increase in the wavenumber of the antisymmetric stretching of -OH and -CH2, suggesting the formation of hydrophobic outer surfaces by n-hexadecyl function. The peaks in the -CH2 rocking band suggest that the HDTMA sorbed at AS had the residual amorphous moieties. In the case of VS-HDTMA, the peak was hidden by a broad peak due to hydrated aluminosilicates in VS. These findings imply that the amorphous moieties of HDTMA sorbed at both soils were affected by residual water in the air dried samples. According to the clay mineralogy of the soils, the greater hydrophobicity in AS-HDTMA was attributed to intercalation of HDTMA into the expansible phyllosilicates in AS. In contrast, the relatively moderate hydrophobicity in VS-HDTMA indicated that the hydrophilic micropores (D < 2 nm) in VS restrict the sorption of HDTMA but enable it to exchange water.
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