We provide a scaling framework describing the different regimes attained by a slit-confined
polymer, undergoing an external pulling force f el, slit. Linear and nonlinear force–extension
relations are discussed in the limit of small and large elongations, resorting to the notion of
self-avoiding pancakes. The crossover to a channellike behavior allows to explain the
scaling of f el, slit as a function of the confinement h observed in recent tug-of-war
experiments. The theoretical analysis provides also a qualitative explanation of DNA …