Researchers from the IAdChem (Institute for Advanced Research in Chemistry) of the Autonomous University of Madrid (UAM) have managed to design a new composite material with better resistance and flexibility, smart in addition, and with nanometric thickness.
By introducing a suitable dopant in an organic polymer acting as a matrix, the fabrication of hybrid materials, also known as composites, can be achieved. This kind of material presents the organic polymer’s mechanical properties and, at the same time, those of the dopant. These new properties can provide them with great utility in several industrial fields.
These materials could allow, for example, that a single piece of it could tell us, with just one look, the temperature inside a refrigerating chamber or the pressure inside a pipeline.
Among these dopants, we must remark the presence of coordination polymers (CPs), a family of compounds with infinite structures formed by metal centers and fragments (both organic and inorganic) acting as ligands.
CPs with staircase-shaped double copper(I)-halide chains can behave like elastic springs when exposed to certain stimuli, their nature being physical, like pressure and temperature; or chemical, like vapors of volatile organic compounds, due to the flexibility of this double chain. Thanks to this stimuli-responsive behavior, these compounds present themselves as excellent dopant for the creation of new hybrid materials.
Recently, the Nanomaterials Group of the Inorganic Chemistry Department of the Autonomous University of Madrid (UAM), with the aid of researchers from CSIC, the University of La Laguna, the University of Valencia and the University of Zaragoza, have published an article in the Chemical Science journal, describing a new nanometer-thick smart hybrid material with high resistance and flexibility, which could be used in temperature and pressure sensors, both in industrial facilities and packaging devices.
INTERESTING PROPERTIES
The new nanomaterial can be obtained by dispersing nanofibers of a copper(I)-iodine based CP with methyl 2-aminoisonicotinate as terminal ligand in a polyvinylidene difluoride (PVDF) matrix.
The studies carried out over this CP show its double copper(I)-iodine chain structure, which provides it with electrical conductivity and an outstanding luminescence when irradiating it with low energy ultraviolet light.
At room temperature, the compound does not show any kind of emission, but when it is cooled to -196 °C (the temperature of liquid nitrogen) it glows with a bright yellow color, returning to its previous state as it warms back to room temperature. However, when the compound is subjected to pressures as high as gigapascals (one gigapascal roughly equals ten thousand times the atmospheric pressure), the emissive behavior completely disappears, also in a reversible way. Both phenomena are due to changes in the interactions between the copper centers, as a consequence of the spring-like behavior displayed by the double chain.
The CP itself is very easy to obtain, since the mixture of copper(I) iodide disolved in acetonitrile with methyl 2-aminoisonicotinate disolved in ethanol leads to an immediate reaction with the concomitant formation of nanofibers of the CP, with lengths of several microns and about five nanometer thick, equivalent to the stacking of 8 single one-dimensional chains. To reach the formation of composites as thin films, starting from these nanofibers is crucial, since their size will determine the minimum thickness of the resulting nanosheet.
The preparation of thin films of the hybrid material was carried out by dispersing the CP nanofibers in a solution of PVDF in dimethylformamide (DMF), and depositing the resulting suspension over silicon oxide by spin-coating (at great speeds, higher than 1000 rpm) or by dip-coating. All of them are homogeneous and share the thermoluminescent properties of the original CP. The mechanical properties of these thin films are currently under study, but they are expected to be close to those of pristine PVDF.
References:
J. Conesa-Egea, et al. 2018. Smart composite films of nanometric thickness based on copper–iodine coordination polymers. Toward sensors. Chem. Sci. DOI: 10.1039/c8sc03085e
