Detachment of semiflexible polymer chains from a substrate: a molecular dynamics investigation (original) (raw)
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Force spectroscopy of polymer desorption: theory and molecular dynamics simulations
Soft Matter, 2014
Forced detachment of a single polymer chain, strongly-adsorbed on a solid substrate, is investigated by two complementary methods: a coarse-grained analytical dynamical model, based on the Onsager stochastic equation, and Molecular Dynamics (MD) simulations with Langevin thermostat. The suggested approach makes it possible to go beyond the limitations of the conventional Bell-Evans model. We observe a series of characteristic force spikes when the pulling force is measured against the cantilever displacement during detachment at constant velocity vc (displacement control mode) and find that the average magnitude of this force increases as vc grows. The probability distributions of the pulling force and the end-monomer distance from the surface at the moment of final detachment are investigated for different adsorption energy ǫ and pulling velocity vc. Our extensive MD-simulations validate and support the main theoretical findings. Moreover, the simulation reveals a novel behavior: for a strong-friction and massive cantilever the force spikes pattern is smeared out at large vc. As a challenging task for experimental bio-polymers sequencing in future we suggest the fabrication of stiff, super-light, nanometer-sized AFM probe.
The Journal of Chemical Physics, 1996
The adsorption of a single polymer chain onto a solid surface is investigated by molecular dynamics simulations. The chain is composed of mass points interacting via a truncated Lennard-Jones potential, i.e., the excluded volume interaction is taken into account, and grafted to the surface with one end. The average adsorption degree is calculated for various chain lengths ͑N ϭ 16, 32, 64, 128͒ and adsorption energies. In addition, the scaling behavior of the adsorption degree and the radius of gyration is investigated. The adsorption degree and the average length of loops and tails are obtained for chains of various stiffnesses. In this context, we find that stiffer chains adsorb more easily. Moreover, the distribution of the mass points perpendicular to the surface as well as the orientation of the bonds with respect to the surface is discussed for various adsorption energies and stiffnesses.
The Detachment of a Polymer Chain from a Weakly Adsorbing Surface Using an AFM Tip
Langmuir, 1999
Atomic force microscopy has been used to investigate the detachment of single polymer chains from surfaces and to measure the picoNewton forces required to extend the chain orthogonal to the surface. Such recent experiments show that the force-extension profiles provide interesting signatures which might be related to the progressive detachment of the chain from a surface. Using equilibrium scaling analysis, activation kinetics, and exactly solvable partition functions we predict force versus extension profiles for various extension rates. We also show how variation in the extension rate can distinguish heterogeneous monomer-surface contacts. The qualitative features that we predict, such as sawtooth force profiles with detachment forces which decrease with extension, maximal yielding forces at high extension rates, and featureless force profiles at large extension, are also seen in experiment.
Dissipative particle dynamics simulations of a single isolated polymer chain in a dilute solution
2019
In this study, we investigate the suitability of dissipative particle dynamics (DPD) simulations to predict the dynamics of polymer chains in dilute polymer solutions, where the chain is represented by a set of beads connected by almost inextensible springs. In terms of behaviour, these springs closely mimic rods that serve as representations of Kuhn steps. We find that the predictions depend on the value of the repulsive parameter for bead-bead pairwise interactions used in the DPD simulations ($a_{ij}$). For all systems, the chain sizes and the relaxation time spectrum are analyzed. For aij=0a_{ij} = 0aij=0, theta solvent behaviour is obtained for the chain size, whereas the dynamics at equilibrium agrees well with the predictions of the Zimm model. For higher values of aija_{ij}aij, the static properties of the chain show good solvent behaviour. However, the scaling laws for the chain dynamics at equilibrium show wide variations, with consistent results obtained only at an intermediate value...
Pulling an adsorbed polymer chain off a solid surface
The European Physical Journal E, 2009
The thermally assisted detachment of a self-avoiding polymer chain from an adhesive surface by an external force applied to one of the chain ends is investigated. We perform our study in the "fixed height" statistical ensemble where one measures the fluctuating force, exerted by the chain on the last monomer when a chain end is kept fixed at height h over the solid plane at different adsorption strength ǫ. The phase diagram in the h − ǫ plane is derived both analytically and by Monte Carlo simulations. We demonstrate that in the vicinity of the polymer desorption transition a number of properties like fluctuations and probability distribution of various quantities behave differently, if h rather than f is used as an independent control parameter. PACS numbers: 82.35.Gh Polymers on surface; adhesion -64.60.A -Specific approaches applied to studies of phase transitions -62.25.+g Mechanical properties of nanoscale systems
Effects of pulling velocity and temperature revealed in polymer pull-out simulations
EPL (Europhysics Letters), 2011
We present a molecular dynamics study of pulling-out polymer chains from ensembles of entangled polymers, with possible applications in single-molecule pulling techniques. The effects of pulling velocity and temperature are identified separately in the adhesive strength G and in the debonding time tD required to completely pull-out the chains from the interface between two polymeric bulks. G is found to have a quasi-static threshold value G0 beyond which it increases linearly with the velocity, while an apparent glass transition temperature is identified in its dependence on temperature. tD has a power law decay with pulling velocity and decreases linearly with temperature. The combination of these independent effects has two remarkable consequences: time-temperature superposition is valid for pull-out experiments, and a master curve exists for the time evolution of the work of adhesion at various temperatures and velocities, by proper normalization.
Large fluctuations of disentaglement force and implications for polymer dynamics
This paper examines the effect of cooling on disentanglement forces in polymers and the implications for both single chain pullout and polymer dynamics. I derive the explicit dependence of the distribution of these forces on temperature, which is found to exhibit a rich behaviour. Most significantly, it is shown to be dominated by large fluctuations up to a certain temperature T0 that can be determined from molecular parameters.
Macromolecules, 1994
A remainingchallenge in the theory of polymer solution dynamics is associated with establishing a relation between the macroscopic hydrodynamic properties of polymer solutions and the molecular structure of the polymer and solvent. This problem is unsolved even for the simplest case of polymer solutions at "infinite dilution". Recent studies have focused on technical problems such as the "preaveraging" approximation, c-expansion truncation errors, and the influence of ternary excluded volume interactions which limit the accuracy of analytic calculations. The present paper examines the role of polymer excluded volume in altering intramolecular hydrodynamic interactions and the possible significance of dynamic chain flexibility on hydrodynamic polymer solution properties. This investigation is aided by analysis of our previous renormalization group (RG) computations and simple exactly solvable models. We also examine experimental trends for the variation of the polymer hydrodynamic interaction with solvent and the variation of the translational friction of small molecules with molecular size. stimulated the introduction of the presumably more molecularly faithful pearl-necklace ("bead") polymer models7-9 with extensions that included hydrodynamic interactions.lOJ1 When hydrodynamic interactions are strong ("nondraining" limit), the pearl-necklace models reduce to the "impermeable sphere model", while for weak hydrodynamic interactions ("free-draining" limit), the Staudinger law (a = 1) is On the other hand, Flory and Fox5 interpreted the variation of a in terms of
Influence of Surface Interactions on Folding and Forced Unbinding of Semiflexible Chains
The Journal of Physical Chemistry B, 2005
We have investigated the folding and forced unbinding transitions of adsorbed semiflexible polymer chains using theory and simulations. These processes describe, at an elementary level, a number of biologically relevant phenomena that include adhesive interactions between proteins and tethering of receptors to cell walls. The binding interface is modeled as a solid surface, and the wormlike chain (WLC) is used for the semiflexible chain (SC). Using Langevin simulations, in the overdamped limit we examine the ordering kinetics of racquet-like and toroidal structures in the presence of an attractive interaction between the surface and the polymer chain. For a range of interactions, temperature, and the persistence length, l p , we obtained the monomer density distribution, n(x), (x is the perpendicular distance of a tagged chain end from the surface) for all of the relevant morphologies. There is a single peak in n(x) inside the range of attractive forces, b, for chains in the extended conformations, whereas in racquet and toroidal structures there is an additional peak at x ≈ b. The simulated results for n(x) are in good agreement with theory.
Macromolecules, 2003
The shear forces between polystyrene chains end-tethered to opposing surfaces have been measured with the surface forces apparatus (SFA) in both good and near-Θ solvents. When the shearing velocity was varied, the complex polymer/solvent system responded in a Newtonian-like fashion with the shear force increasing linearly with the shear velocity. The effective viscosity of the end-tethered systems in this Newtonian-like regime was found to be an order of magnitude greater than the viscosity of semidilute solutions of equivalent molecular weight free chains. At larger shear velocities or higher extents of compression, Brownian dynamics simulations suggest the interfacial width will thin, leading to a sublinear increase in the shear force with sliding velocity. Experimental limitations prevented exploration of the higher shear velocities simulated with the Brownian dynamics approach, but increasing confinement eventually did lead to sublinear behavior, in agreement with the simulation prediction.