Simulated microgravity for controlled materials engineering

In chemical reactions, stirring is often used to improve the efficiency of mass transport of reagents via turbulent flows. However, this can lead to poor control of convective transport processes, causing the precipitation of reaction products and negatively impacting reaction performance. This is particularly problematic in the synthesis of 2D and 3D functional crystals with controlled sizes and shapes, such as metal-organic frameworks (MOFs). Buoyancy-driven convection generated by the depletion of monomer solution during MOF crystal formation can lead to uneven growth rates and precipitation of crystals in solution, ultimately affecting the uniformity and control of MOF crystal growth. Surface-templated growth methods and interfacial synthetic approaches are alternative methods, but they too can suffer from non-controlled convective transport processes, leading to poor control over the MOF’s morphology and function.

Studies at the International Space Station have shown that microgravity conditions can greatly favor the growth of crystalline matter, resulting in larger crystalline domain sizes, lower defect densities, and new morphologies. However, experimentation in space is costly and access is limited. To overcome these challenges, researchers have developed a microfluidic approach to simulate the effect of microgravity on Earth, allowing for the controlled synthesis and growth of MOFs. The development of microfluidic devices provides a cost-effective and accessible method for studying and controlling the engineering of crystalline porous molecular frameworks, ultimately leading to improved control over their morphology and function.