(180m) Particle On a String: Equilibrium Behavior of Surface-Tethered Particles by Monte Carlo Simulation

We consider the behavior of the “particle on a string” system, comprising a single colloid-sized particle tethered to a flat surface by a single polymer chain. We are interested in understanding the equilibrium averages of the polymer dimensions as functions of the relative size of the tethered particle. This is relevant to the interpretation of tethered particle motion experiments, wherein the motion and position of the tethered particle are used as reporters on the conformational properties of the underlying polymer molecule. Monte Carlo computer simulations are used to observe the behavior of this system with both random walk and self-avoiding walk polymer models. Our results reveal an unanticipated richness in the system behavior. We find two local maxima in the expansion factor of the polymer tether as a function of particle size, with both random walk and self-avoiding walk models. Furthermore, this non-monotonic behavior persists to very large particle sizes before the expected asymptotic “parallel plate” limit is reached.