Escape transition of a compressed polymer mushroom under good solvent conditions

The escape transition of a flexible polymer chain of chain length N, endgra fted at a hard wall and compressed by a piston of radius R, is studied by M onte Carlo simulation and by phenomenological arguments. In contrast to pre vious theories which have considered the transition as a function of a (fix ed) 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 fi nd that the transition (which is sharp only for N --> infinity) is characte rized by a flat region of f in the f vs. H isotherm, i.e. a jump in the hei ght occurs at the transition from H-esc,H-t to H-imp,H-t, with (H-imp,H-t - H-esc,H-t)/H-esc,H-t approximate to 0.26.