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Article

Forward Flux Sampling of Polymer Desorption Paths from a Solid Surface into Dilute Solution

1
Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109-2136, USA
2
Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2136, USA
*
Author to whom correspondence should be addressed.
Polymers 2020, 12(10), 2275; https://doi.org/10.3390/polym12102275
Received: 31 August 2020 / Revised: 24 September 2020 / Accepted: 24 September 2020 / Published: 3 October 2020
(This article belongs to the Special Issue Theory of Polymers at Interfaces)
We compute desorption rates for isolated polymers adsorbed to a solid wall with a rare event sampling technique called multilevel splitting, also known as forward flux sampling. We interpret computed rates with theories based on the conjecture that the product tdesDRg2 of the desorption time tdes and diffusivity D divided by squared radius of gyration Rg scales with exp(h/Rg) where h is the equilibrium ratio of adsorbed surface concentration of polymer Γ to bulk concentration of polymer c. As the polymer–wall interaction energy is increased, the slope of lntdesDRg2 vs. NVMFkBT nearly approaches unity, as expected for strongly-adsorbing chains, where N is the degree of polymerization and VMF is the height-averaged monomer–wall interaction energy for a strongly adsorbed chain. However, we also find that this scaling law is only accurate when adsorption strength per monomer exceeds a threshold value on the order of 0.3–0.5 kBT for a freely jointed chain without or with excluded volume effects. Below the critical value, we observe that tdesDRg2 becomes nearly constant with N, so that tdesNα, with α2. This suggests a crossover from “strong” detachment-controlled to a “weak” diffusion-controlled desorption rate as VMF/kBT drops below some threshold. These results may partially explain experimental data, that in some cases show “strong” exponential dependence of desorption time on chain length, while in others a “weak” power-law dependence is found. However, in the “strong” adsorption case, our results suggest much longer desorption times than those measured, while the reverse is true in the weak adsorption limit. We discuss possible reasons for these discrepancies. View Full-Text
Keywords: polymer desorption; forward flux sampling; Langevin dynamics simulations polymer desorption; forward flux sampling; Langevin dynamics simulations
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MDPI and ACS Style

Huston, K.J.; Rice, C.E.; Larson, R.G. Forward Flux Sampling of Polymer Desorption Paths from a Solid Surface into Dilute Solution. Polymers 2020, 12, 2275. https://doi.org/10.3390/polym12102275

AMA Style

Huston KJ, Rice CE, Larson RG. Forward Flux Sampling of Polymer Desorption Paths from a Solid Surface into Dilute Solution. Polymers. 2020; 12(10):2275. https://doi.org/10.3390/polym12102275

Chicago/Turabian Style

Huston, Kyle J., Christina E. Rice, and Ronald G. Larson. 2020. "Forward Flux Sampling of Polymer Desorption Paths from a Solid Surface into Dilute Solution" Polymers 12, no. 10: 2275. https://doi.org/10.3390/polym12102275

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