Understanding the mechanisms of soil water repellency from nanoscale to ecosystem scale : a review

Purpose: Soil water repellency (SWR) can interrupt water infiltration that may decline plant growth and potentially trigger soil erosion. Until now research has been mainly focused on understanding the mechanisms of SWR at different scales by observation and modelling studies. Materials and methods: This review systematically discusses the possible mechanisms at different scales of the occurrence and persistence of SWR from nanoscale to ecosystem scale. Results and discussion: Soil characteristics are strongly related to the severity of SWR, particularly in soil organic matter and soil moisture. The presence of a higher amount of hydrophobic organic compounds and lower soil moisture content lead to higher water repellency, suggesting that the interaction at the nanoscale between organic compounds and water molecules primarily determines the persistence of SWR. The repeated alternation of drying-wetting process largely modifies the relationship between water molecules and soil particles that impacts the possibility of SWR from hydrophilic in wet condition to hydrophobic in dry condition. Within ecosystem scale, vegetation and microbes are original sources of SWR-inducing compounds influencing the distribution and prevalence of SWR. Nevertheless, the challenge of global climate change, drought and warming can increase SWR. Extreme SWR induces more serious runoff and overland flow that is enhanced by intensive precipitation. Conclusions: We conclude that understanding the interaction of water molecules and organic compounds at soil particle surface is essential to understand SWR at the nanoscale. Expanding the mechanisms of SWR from nanoscale to a larger scale is fundamental to improve the remediation of soil pollution and mitigate global change

Understanding the mechanisms of soil water repellency from nanoscale to ecosystem scale: a review

Purpose: Soil water repellency (SWR) can interrupt water infiltration that may decline plant growth and potentially trigger soil erosion. Until now research has been mainly focused on understanding the mechanisms of SWR at different scales by observation and modelling studies. Materials and methods: This review systematically discusses the possible mechanisms at different scales of the occurrence and persistence of SWR from nanoscale to ecosystem scale. Results and discussion: Soil characteristics are strongly related to the severity of SWR, particularly in soil organic matter and soil moisture. The presence of a higher amount of hydrophobic organic compounds and lower soil moisture content lead to higher water repellency, suggesting that the interaction at the nanoscale between organic compounds and water molecules primarily determines the persistence of SWR. The repeated alternation of drying-wetting process largely modifies the relationship between water molecules and soil particles that impacts the possibility of SWR from hydrophilic in wet condition to hydrophobic in dry condition. Within ecosystem scale, vegetation and microbes are original sources of SWR-inducing compounds influencing the distribution and prevalence of SWR. Nevertheless, the challenge of global climate change, drought and warming can increase SWR. Extreme SWR induces more serious runoff and overland flow that is enhanced by intensive precipitation. Conclusions: We conclude that understanding the interaction of water molecules and organic compounds at soil particle surface is essential to understand SWR at the nanoscale. Expanding the mechanisms of SWR from nanoscale to a larger scale is fundamental to improve the remediation of soil pollution and mitigate global change

Interactions between a Series of Pyrene End-Labeled Poly(ethylene oxide)s and Sodium Dodecyl Sulfate in Aqueous Solution Probed by Fluorescence

The interactions between a series of poly­(ethylene oxide)­s covalently labeled at both ends with pyrene pendants (PEO­(<i>X</i>)-Py₂, where <i>X</i> represents the number-average molecular weight of the PEO chains and equals 2K, 5K, 10K, and 16.5K) and an ionic surfactant, namely, sodium dodecyl sulfate (SDS), in water were investigated at a fixed pyrene concentration of 2.5 μM corresponding to polymer concentrations smaller than 21 mg/L and with an SDS concentration range between 5 × 10^–6 and 0.02 M, thus encompassing the 8 mM critical micelle concentration (CMC) of SDS in water. The steady-state fluorescence spectra showed that the <i>I</i>₁/<i>I</i>₃ ratio decreased from 1.73 ± 0.06 for SDS concentration smaller than 2 mM where pyrene was exposed to water to 1.43 ± 0.03 for SDS concentration greater than 6 mM where pyrene was incorporated inside SDS micelles. The ratio of excimer-to-monomer emission intensities (the <i>I</i>_E/<i>I</i>_M ratio) of all PEO­(<i>X</i>)-Py₂ samples remained constant at low SDS concentrations, then increased, passed through a maximum at the same SDS concentration of 4 mM before decreasing to a plateau value that is close to zero for PEO­(10K)-Py₂ and PEO­(16.5K)-Py₂ but nonzero for PEO­(2K)-Py₂ and PEO­(5K)-Py₂. The pyrene end groups of these two latter samples could not bridge two different micelles due to the short PEO chain, and excimer was formed by intramolecular diffusion inside the same SDS micelle. Time-resolved fluorescence decays of the pyrene monomer and excimer of the PEO­(<i>X</i>)-Py₂ samples were acquired at various SDS concentrations and globally fitted according to the “Model Free” analysis over the entire range of SDS concentration. The molar fractions of various excited pyrene species and the rate constant of pyrene excimer formation retrieved from the analysis of fluorescence decays were obtained as a function of SDS concentration. Interactions between SDS and PEO could not be detected by isothermal titration calorimetry, potentiometry with a surfactant selective electrode, and conductance measurements

Self-Assembly Behavior of Thermoresponsive Oligo(ethylene glycol) Methacrylates Random Copolymer

A well-defined random copolymer containing 2-(2-methoxyethoxy) ethyl methacrylate (MEO₂MA, <i>M</i>_n = 188 g/mol) and poly­(ethylene glycol) methyl ether methacrylate (PEGMA, <i>M</i>_n = 2080 g/mol) (poly­(MEO₂MA-<i>co</i>-PEGMA₂₀₈₀)), <i>M</i>_n = 17300 g/mol) was synthesized using the atom transfer radical polymerization (ATRP) process, and its thermoresponsive behaviors in aqueous solution were investigated. In comparison to other temperature-sensitive random copolymers based on oligo­(ethylene glycol) methacrylates, this copolymer exhibited an unusual thermally induced two-stage aggregation process. The copolymer chains associate at the first thermal transition followed by a rearrangement process at the second thermal transition to produce a stable core–shell micellar structure. The morphology of the micelle comprises of a methacrylate core stabilized by the longer ethylene glycol segments (<i>M</i>_n = 2080 g/mol) shell