Configuration Dynamics Of Polymer Chain In Active System

Active matters consisting of active particles are an important class of non-equilibrium systems,ranging from bacteria colonies to animal flocks.Different from a passive particle,an active one takes up energy from the environment and converts the energy into the particle directed motion.Due to unique property of active motion,active matter systems often exhibit exotic behaviors not found in passive systems.As the configuration dynamics of a polymer chain in an active bath has gained extensive attention in recent years,in the present thesis we have used computer simulations to investigate the configuration dynamics of a polymer chain in different active baths.1.Configuration dynamics of a flexible polymer chain in a bath of chiral active particlesIn the past years,the study of polymer dynamics in an active bath has not involved the chiral property of the active particles.To address this issue in this thesis,we have investigated the influence of a chiral active bath on the configuration dynamics of a polymer chain.The result shows that the radius of gyration of the polymer chain swells with increasing the activity of the achiral active particles.While the chain first collapses into a small compact cluster and then swells again with increasing the activity of the chiral active particles.More interestingly,the polymer can even form a closed ring if the chain length is large enough.Consequently,the gyration radius of the polymer chain shows nontrivial non-monotonic dependences on the activity of the environment particles,i.e.,it undergoes a minimum for relatively short chains and two minima with a maximum in between for longer chains.Our analysis shows that such interesting phenomena are mainly due to the competition between two roles played by the chiral active bath:while the persistence motion due to particle activity tends to stretch the chain,the circular motion of the particle may lead to an effective osmotic pressure that tends to collapse the chain.2.Size effect of active particles on polymer configuration dynamicsIn majority of the studies,active crowders were treated as spherical particles of fixed sizes.Surely in real systems,the crowders could have different sizes or even shapes.Here we investigate a polymer chain immersed in a bath of size-changed active crowders in two dimensional space using Langevin dynamics simulations.We find that the radius of gyration of the polymer chain shows nontrivial non-monotonic dependence on the size of active crowders:the chain first swells upon increasing particle size,reaching a fully expanded state,and then decreases until the chain collapse into a compact cluster.Analysis shows that it is the competition between two effects of active crowders,one stretching the chain from inside due to persistence motion and the other compress the chain from outside,that leads to the non-monotonic dependence.Besides,the diffusion of the polymer chain also shows nontrivial non-monotonic dependence on crowder size.