End-tethered polymer chains under AFM tips: Compression and escape in theta solvents

We study the problem of an isolated end-grafted polymer chain confined under a finite-sized flat obstacle in a Theta solvent. For obstacles that are not too large this chain can undergo an escape transition where part of the chain remains trapped and the remainder escapes from under the obstacle. The spinodals of this system are influenced by the presence of a three-body term. We also study the problem of a chain under a tilted obstacle. We show that in this case there are two different escape possibilities. The system can then undergo the following series of transitions C --> E --> C --> E as the chain is compressed, where C = confined and E = escaped.