Interaction between a grafted polymer chain and an AFM tip: Scaling laws, forces, and evidence of conformational transition

The force of compression of an end-grafted polymer chain in a Theta solvent by a finite-sized object (e.g., the tip of an atomic force microscope) is studied using a new simulation technique called the contact-distribution method. This paper presents the first ever simulation of the conformational transition of a polymer chain from a "confined" state to an "escaped" state. The results corroborate the force relations that were recently obtained using scaling arguments but clearly indicate the existence of a transition region between the two states. The characteristics of the transition are affected by the size, shape, and alignment of the tip and by the temperature or quality of the solvent. We also comment on the implication of the results to the experimental confirmation of the predictions.