In a study that could finally help the plants survive the dry season, the scientists Princeton University has found the key reason that a mixture of so-called hydrogen and soil is sometimes proven to be disappointing for farmers.
Hydrogel beads, small plastic lumps that can absorb a thousand times the weight of water, seem suitable for use as a small underground water reservoir. In theory, when the soil is dry, hydrogen releases water to hydrate the plant roots, thus eliminating drought, saving water, and boosting yields.
Yet mixing hydrogels into farmers’ gardens has been successful. Scientists have struggled to explain this uneven performance in large part because the soil – becoming opaque – has hampered efforts to observe, analyze, and ultimately improve hydrogen behavior.
In a new study, Princeton researchers demonstrated an experimental platform that allows scientists to study hydrogen-secrecy that is hidden in the ground, and the environment that is enclosed, enclosed again. The platform relies on two materials: a transparent granular medium – a glass bead wrapper – as a stand-in ground, and water is added by a chemical called ammonium thiocyanate. Clever chemicals change the way water turns light, offset the effects of distortion of the usual round glass beads. Upshot is the researcher can see directly into the color hydrogol globe in the middle of the fake ground.
“In particular, my laboratory finds the right chemicals at the right concentration to change the optical properties of liquids,” said Sujit Datta, assistant professor of chemical and biological engineering at Princeton and senior author of the journal’s research. Advances in Science on February 12, 2021. “This capability allows 3D visualization of fluid flow and other processes that occur in inaccessible, opaque media, such as soil and rock.”
Scientists use the setting to show that the amount of water stored by hydrogels is controlled by the balance between the forces applied when hydroglog swells the water and the trapping force of the surrounding soil. As a result, softer hydrogels absorb large amounts of water when mixed into the soil layer, but do not work in the deeper soil layers, where they experience greater pressure. Conversely, hydrogels that have been synthesized become closer internally, and as a result are more rigid and can provide greater strength to the soil when absorbing water, will be more effective in the deeper layers. Datta said that, guided by these results, engineers will now be able to conduct further experiments to adjust the hydrogen chemistry to specific crops and soil conditions.
“Our results provide guidelines for designing hydrogels that can optimally absorb water depending on the soil intended to be used, potentially helping more demand for food and water,” said Datta.
The inspiration for learning comes from Datta learning about the enormous promise of hydrogen in agriculture but also its failure to fulfill it in some cases. Seeking the development of a platform to investigate the behavior of hydrogels on the ground, Datta and colleagues started with a fake ground of borosilicate glass beads, usually used for some bioscience research and, in everyday life, costume jewelry. The size of the beads ranged from one to three millimeters in diameter, corresponding to the grain size of the loose soil, wrapped.
When researchers add an aqueous solution of ammonium thiosianate, it clears the distortion caused by borosilicate glass beads and allows a clear view of hydrogogels. Credit: Datta et al / Princeton University
In the summer of 2018, Datta commissioned Margaret O’Connell, then a Princeton undergraduate student in her lab through the Princeton’s ReMatch + program, to identify additives that would alter the refractive index of water to compensate beads’ light distortion, but still allow hydrogogels to be effective absorb water. O’Connell is small to a solution of water with slightly heavier and contributed by ammonium thiosianate.
Nancy Lu, a graduate student at Princeton, and Jeremy Cho, then a graduate of the Datta lab and now an assistant professor at the University of Nevada, Las Vegas, built an early version of the experimental platform. They placed a colored hydrogel ball, made of a conventional hydrogog material called polyacrylamide, in the center of the bead and collected some initial observations.
Jean-Francois Louf, a postdoctoral researcher at the Datta lab, then created a second version of the platform and conducted experiments that were reported in the study. This final platform consists of a piston that is weighed to produce pressure on top of the beads, adapting to some of the pressure that the hydrogel will press on the ground, depending on the depth of the hydrogogel set.
In general, the results indicate the relationship between hydrogen and soil, based on their respective properties. The theoretical framework developed by the team to capture these behaviors will help explain the shortened field results collected by other researchers, where harvest yields sometimes increase, but hydrogen times show minimal benefits or even reduce the natural compaction of the soil, increasing the risk of erosion.
Ruben Juanes, a professor of civil and environmental engineering at the Massachusetts Institute of Technology who is not involved in the study, offers comments on its importance. “This work opens up an attractive opportunity for the use of hydrogen as a ground capacitor that modulates the availability of water and controls the release of water into the roots of crops, in a way that can provide true technological advances in sustainable agriculture,” said Juanes.
Other hydrogen applications can improve the performance of Datta and her friends. Examples include oil refining, filtration, and the development of new building materials, such as concrete-filled hydrogels to prevent over-drying and cracking. One of the promising areas in particular is biomedical, with applications ranging from drug delivery to wound healing and artificial tissue engineering.
“Hydrogels are a versatile, versatile material that also works well,” said Datta. “But while most lab studies focus on them in unconfigured settings, many applications involve their use in a narrow and limited space. We are very interested in this simple experimental platform because it allows us to see what others cannot see.”
Reference: 12 February 2021, Advances in Science.
This work is partially supported by the National Science Foundation and the High Meadows Environmental Institute in Princeton.