A computational model for active transport: diffusion in active matter

In recent years, active matter has gained importance as a research subject in numerous scientific contexts. Active matter refers to active ‘agents' that consume energy to move and exert mechanical forces and it is a suitable definition for numerous systems of biological origin, starting with bacterial colonies and moving through all scales of reality up to animal macrosystems, such as flocks of birds or schools of fish. Active matter is an important object of study to understand the behaviour of this type of systems and more generally to find a way to artificially create synthetic models that exploit artificial self-propelled particles. Currently, active matter is used in industrial areas such as drug delivery, heat transport or liquid crystals for screens. This project focuses on the characterization of a transport coefficient for an active molecule in confined space. The liquid crystal dimer 1",7"-bis(4-cyanobiphenyl-4'-yl) heptane, also abbreviated as CB7CB, is a paradigmatic example of a liquid crystal, used in the field of LCD screen technology, that exhibits a transition phase between a nematic and a twisted-bend nematic phase. In this project, we propose a coarse-grained model of a CB7CB molecule, and we study its behaviour in confined solvents at a controlled temperature. Also, we model its active behaviour by imposing a force exerted on the molecule in a preferential direction, mimicking the transformation of internal energy into work. By changing the force exerted on the molecule, we measure the 'active' translational diffusion coefficient of CB7CB. The dependence between the force exerted and the measured diffusion coefficient shows a rich behaviour open for further research.