2009/09/13 by Andrey Milchev, V. G. Rostiashvili, Milchev, A. +5
Chemical Engineering · Materials Science · Physics and Astronomy · #FOS: Physical sciences #Force Microscopy Techniques and Applications #Polymer crystallization and properties #Rheology and Fluid Dynamics Studies #Soft Condensed Matter (cond-mat.soft) #Statistical Mechanics (cond-mat.stat-mech)
paper · pdf · doi:10.48550/arxiv.0909.2435
openalex publication_date 2009/09/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We show that when a self-avoiding polymer chain is pulled off a sticky surface by force applied to the end segment, it undergoes a first-order thermodynamic phase transition albeit without phase coexistence. This unusual feature is demonstrated analytically by means of a Grand Canonical Ensemble (GCE) description of adsorbed macromolecules as well as by Monte Carlo simulations of an off-lattice bead-spring model of a polymer chain. Theoretical treatment and computer experiment can be carried out both in the constant-force f statistical ensemble and in the constant-height h ensemble. We find that the force-assisted desorption undergoes a first-order dichotomic phase transition whereby phase coexistence between adsorbed and desorbed states does not exist. In the f-ensemble the order parameter (the fraction of chain contacts with the surface) is characterized by huge fluctuations when the pulling force attains a critical value fD. In the h-ensemble, in contrast, fluctuations are always finite at the critical height hD. The derived analytical expressions for the probability distributions of the basic structural units of an adsorbed polymer, such as loops, trains and tails, in terms of the adhesive potential and f or h, provide a full description of the polymer structure and behavior upon force-assisted detachment. In addition, one finds that the hitherto controversial value of the universal critical adsorption exponent ϕdepends essentially on the extent of interaction between the loops adsorbed chain so that ϕmay vary within the limits 0.39 < ϕ< 0.59.