The Escape Transition of a Compressed Star Polymer: Self-Consistent Field Predictions Tested by Simulation

Abstract

The escape transition of a polymer "mushroom" (a flexible chain grafted to a flat nonadsorbing substrate surface in a good solvent) occurs when the polymer is compressed by a cylindrical piston of radius R, that by far exceeds the chain gyration radius. At this transition, the chain conformation abruptly changes from a two-dimensional selfavoiding walk of blobs (of diameter H, the height of the piston above the substrate) to a "flower conformation", i.e., stretched almost one-dimensional string of blobs (with end-to-end distance ≈ R) and an "escaped" part of the chain, the "crown", outside the piston. The extension of this problem to the case of star polymers with f arms is considered, assuming that the center of the star is grafted to the substrate. The question is considered whether under compression the arms escape all together or whether there occurs an arm by arm escape under increasing compression. Both self-consistent field calculations and molecular dynamics simulations are found to favor the latter scenario.

Arm retraction and escape transition in semi-flexible star polymer under cylindrical confinement

“…Interpretations important for star-shape-like behavior were pointed out also within the free energy studies of condensed system of linear chains [36]. Very recently, an equilibrium distribution of the arms of a 3-arm polymer in a cylindrical confinement was explored for the first time by means of computer simulations [37], and a case of a pressurized molecule under the tip of an AFM probe has been simulated [38].…”

The escape transition in a self-avoiding walk model of linear polymers

“…The model in figure 1 is a lattice version of models examined in a series of excellent papers [8,12,21,24] exploring the scaling and transition in linear and star polymers compressed by a piston. Additional numerical results on star polymers can be found in references [26,27].…”

“…Additional numerical results on star polymers can be found in references [26,27]. These studies are of bead-spring models [21], lattice models [12], and molecular dynamics simulations [24]. While an escape transition is not established rigorously in these models, there are ample numerical evidence in these models of such a transition.…”

The escape transition in a self-avoiding walk model of linear polymers

“…The model in figure 1 is a lattice version of models examined in a series of excellent papers [11][12][13][14] exploring the scaling and transition in linear and star polymers compressed by a piston. Additional numerical results on star polymers can be found in [15,16].…”

“…Additional numerical results on star polymers can be found in [15,16]. These studies are of bead-spring models [12], lattice models [13], and molecular dynamics simulations [14]. While an escape transition is not established rigorously in these models, these studies give ample numerical evidence of such a transition.…”