  The interaction between polymer brush and colloidal particles has been
intensively studied in the last two decades. Here we consider a flat
chain-grafted substrate immersed in a bath of active particles. Simulations
show that an increase in the self-propelling force causes an increase in the
number of particles that penetrate into the brush. Anomalously, the particle
density inside the main body of the brush eventually becomes higher than that
outside the brush at very large self-propelling force. The grafted chains are
further stretched due to the steric repulsion from the intruded particles. Upon
the increase of the self-propelling force, distinct stretching behaviors of
chains were observed for low and high grafting densities. Surprisingly, we
found a weak descent of the end-to-end distance of chains for high grafting
density and very large force which is reminiscent of the compression effect of
a chain in the active bath.
