Adsorption of finite semiflexible polymers and their loop and tail distributions

TL;DR

This paper investigates how semiflexible polymers adsorb onto surfaces, analyzing the effects of polymer length, flexibility, and confinement on adsorption thresholds, loop and tail distributions, and provides methods to interpret experimental data.

Contribution

It introduces a comprehensive analysis of finite semiflexible polymer adsorption, including new regimes, finite size corrections, and loop/tail distribution exponents, applicable to experimental systems like actin.

Findings

Identified three adsorption regimes based on persistence length and potential range.

Derived power law exponents for loop and tail distributions.

Provided a method to analyze experimental adsorption data for semiflexible polymers.

Abstract

We discuss the adsorption of semiflexible polymers to a planar attractive wall and focus on the questions of the adsorption threshold for polymers of {\it finite} length and their loop and tail distributions using both Monte-Carlo simulations and analytical arguments. For the adsorption threshold, we find three regimes: (i) a flexible or Gaussian regime if the persistence length is smaller than the adsorption potential range, (ii) a semiflexible regime if the persistence length is larger than the potential range, and (iii) for finite polymers, a novel crossover to a rigid rod regime if the deflection length exceeds the contour length. In the flexible and semiflexible regime, finite size corrections arise because the correlation length exceeds the contour length. In the rigid rod regime, however, it is essential how the global orientational or translational degrees of freedom are restricted by grafting or confinement. We discuss finite size corrections for polymers grafted to the adsorbing surface and for polymers confined by a second (parallel) hard wall. Based on these results we obtain a method to analyze adsorption data for finite semiflexible polymers such as filamentous actin. For the loop and tail distributions, we find power laws with an exponential decay on length scales exceeding the correlation length. We derive and confirm the loop and tail power law exponents for flexible and semiflexible polymers. This allows us to explain that, close to the transition, semiflexible polymers have significantly smaller loops and both flexible and semiflexible polymers desorb by expanding their tail length. The tail distribution allows us to extract the free energy per length of adsorption for actin filaments from experimental data [D. Welch et al., Soft Matter 11, 7507 (2015)].