A team of researchers demonstrated that 2D porous crystalline molecular frameworks (MOFs) can be grown with excellent control over their morphology and homogeneity by using a custom-made microfluidic device.
This approach recreates on Earth the microgravity environment of laboratories on the International Space Stations.
Crystallization studies conducted in space laboratories, which are costly and unaffordable for most research laboratories, showed the valuable effects of microgravity during the crystal growth process and the morphogenesis of materials. The absence of convective mass transport processes favours the synthesis of larger samples of material, with less defects and an improved control over their morphology. Producing crystalline materials on the Space Station on a regular basis is, of course, unviable, as it is both non-practical and very expensive.
Now, a research study led by a scientific team of the University of Barcelona, in which ICMAB Researcher Raphael Pfattner has collaborated, has created an easy and efficient method to achieve experimentation conditions of microgravity on Earth that simulate those in space. The results were published in the journal Advanced Materials in an article highlighted on its front cover.
To get these simulated microgravity conditions, the researchers used custom-made microfluidic devices with which they created the 2D porous crystalline molecular structures. According to Josep Puigmartí Luis, ICREA researcher at the Department of Physical Chemistry and member of the Institute of Theoretical and Computational Chemistry (IQTCUB), “we confirmed that the experiments under these simulated microgravity conditions have unprecedented effects on the orientation, compactness and generation of 2D crystalline and porous materials”.
Prof. Puigmartí-Luis, from the UB, Dr. Daniel Ruiz-Molina, from ICN2, Dr. Tiago Sotto Mayor, from Porto University, and Dr. Raphael Pfattner, from the Institue of Materials Science of Barcelona (ICMAB-CSIC), have coordinated this multidisciplinary project, which also involved researchers from the ALBA Synchrotron, ETH Zurich, the University of Newcastle (Australia) and the “Sapienza” University of Rome (Italy).
To create this new system, the research team designed a microfluidic device which consists of two interlinked substrates with a fine silicone film with variable thicknesses (from 200 to μm). The objective was to create a microfluidic environament of 6 cm long and 1.5 cm wide. One of the surfaces has two machine inlet ports that enable the complete filling of the microfluidic environment and prevent the appearance of air bubbles. The system enabled the growth of a 2D metalorganic framework prototype (MOF) of Ni3(HITP)2 composition, which forms a millimetric layer without defects with conductivity properties that act at a long distance under environmental conditions.
While the same reaction performed in standard laboratory conditions leads to precipitation of some components and irregular growth, the use of this microfluidic device allow controlling the steps of the process and obtaining a greatly better outcome. This confirms the authors’ intuition, supported by numerical simulation, that the environment created in this device reproduces what observed in the experiments conducted on the ISS as an effect of microgravity conditions.
"The spatio-temporal control in the growth of this material obtained with the simulated microgravity conditions is unprecedented in the scientific literature. The microfluidic device has allowed us to develop centimetre-long thin layers and study the previously undescribed electronic properties of the material," explains Noemí Contreras Pereda, from ICN2.
Other structures were synthetized by functionalising the surface in various ways or using different reactants, to explore the versatility of this approach. It proved efficient in growing homogeneous and large thin films of crystalline materials in a wide variety of substrates, with a remarkable control over their orientation and morphology. “This new simulated microgravity system will be like a ‘playground’ for chemists, physicists, and materials scientists who want to process high-quality samples of 2D crystalline functional devices and materials”, concludes the researcher.
Synthesis of 2D Porous Crystalline Materials in Simulated Microgravity.
Noemí Contreras-Pereda, David Rodríguez-San-Miguel, Carlos Franco, Semih Sevim, João Pedro Vale, Eduardo Solano, Wye-Khay Fong, Alessandra Del Giudice, Luciano Galantini, Raphael Pfattner, Salvador Pané, Tiago Sotto Mayor, Daniel Ruiz-Molina, and Josep Puigmartí-Luis.
Advanced Materials, June 2021.
Advanced Materials Volume 33, Issue 30. 28 July 2021.