Microscale mixing without turbulence

In turbulent fluids, mixing of the components happens easily. However, in more viscous fluids such as those enclosed within cellular compartments, the intermixing of particles and molecules is much more challenging. As time also plays a role in such systems, the slow mixing by molecular movement is typically not sufficient and efficient stirring strategies are thus required to maintain functionality.

In the department of Living Matter Physics at MPI-DS, scientists investigated the universal physical principles underlying such mixing dynamics. They identified protocols that allow for the optimal mixing of the system when energetic costs or fluid motion are limiting factors.

“We found that the most effective stirring strategies share a universal structure and are symmetric in time,” says Luca Cocconi, first author of the study. “These optimal protocols reveal a fundamental limit on how efficiently information – for example about the identity and position of particles - can be erased in such systems.”

“We could derive explicit results without resorting to simulations,” explains Andrej Vilfan, last author of the study. “This is remarkable since such optimization problems are often not solvable analytically,” he continues.

Overall, the study deepens the understanding of mixing dynamics in both cellular and in microfluidic systems. At the same time, it provides a theoretical framework to design efficient mixing strategies in engineering at the microscale.