Hydrophobic-hydrophilic surface switching properties of nonchain extended poly(urethane)s for use in agriculture to minimize soil water evaporation and permit water infiltration

Preformed plastic films produced from nondegradable materials such as poly(ethylene) are widely used in agriculture to enhance crop production by modifying soil temperature, conserving soil water, and supressing weeds, but are generally removed and disposed of after each growing season. We aim to circumvent the need to retrieve and dispose of plastic films by using water-borne, degradable polymers that can be sprayed directly onto the soil surface to form a barrier to reduce soil water evaporation. We report the synthesis and characterization of a series of nonchain extended poly(urethane)s (PUs) for this purpose, that were prepared from poly(dimethylsiloxane) (928.3 g mol(-1)) and poly(ethylene glycol) (1020 g mol(-1)). These new materials undergo hydrophobic-hydrophilic switching of their surface properties when in contact with water, which we exploit as a means of minimizing water evaporation from soil when the polymer layer is dry (e.g., in sunny conditions), but permitting the infiltration of liquid water through the treatment into soil during rainfall or sprinkler irrigation. The surface wettability and restructuring phenomena leading to these fascinating properties are intensively investigated using water contact angle measurements, surface-free energy estimates and depth profiling X-ray photoelectron spectroscopy (XPS). Laboratory pot trials demonstrate that soil water evaporation reduced by more than 70% when soil was treated with a low loading of the polymer. (C) 2016 Wiley Periodicals, Inc.