Reconstruction of Soil Components into Multifunctional Freestanding Membranes.

Multifunctional freestanding membranes are prepared by tuning the structure of ubiquitous soil components, viz. clay and humic acids. Cross-linking of exfoliated clay layers with purified humic acids not only conferred mechanical strength but also enhanced chemical robustness of the membranes. The percolated network of molecularly sized channels of the soil membranes exhibits characteristic nanofluidic phenomena. Electrical conductivity is induced to otherwise insulating soil membranes by heating in an inert atmosphere, without affecting their nanofluidic ionic conductivity. The soil membranes also provided a new platform to prepare and study mixed conducting materials. Strips of heated membranes are shown to exhibit excellent sensitivity toward NH3 gas under atmospheric conditions.

Strategic Shuffling of Clay Layers to Imbue Them with Responsiveness.

Layers of naturally occurring clay minerals are rearranged to prepare highly sensitive multiresponsive clay-clay bilayer membrane (CCBM). The CCBM introduced here responds to the minuscule changes in the surrounding environments including temperature, humidity, and presence of solvent vapors by morphing in specific manners. Strips cut from CCBM exhibit up to 588 N kg-1 force output when exposed to temperature fluctuations. Inheriting the natural stability of clay minerals, CCBM demonstrates extreme robustness, heating up to 500 °C, cooling with liquid N2 and exposure to corrosive chemical vapors did not deteriorate its bending performance. Mechanistic studies suggest that shape transformations of CCBM are driven by the unequal response of its components to external stimuli.