Escape transition of a compressed polymer mushroom under good solvent conditions

The escape transition of a flexible polymer chain of chain length N , endgrafted at a hard wall and compressed by a piston of radius R , is studied by Monte Carlo simulation and by phenomenological arguments. In contrast to previous theories which have considered the transition as a function of a (fixed) height H of the piston above the wall, we consider the transition as a function of the conjugate variable, the force f acting on the piston. We find that the transition (which is sharp only for N → ∞) is characterized by a flat region of f in the f vs. H isotherm, i.e. a jump in the height occurs at the transition from H esc, t to H imp, t , with ( H imp, t − H esc, t )/ H esc, t ≈ 0.26.