Transitions of tethered polymer chains: A simulation study with the bond fluctuation lattice model

Abstract

A polymer chain tethered to a surface may be compact or extended, adsorbed or desorbed, depending on interactions with the surface and the surrounding solvent. This leads to a rich phase diagram with a variety of transitions. To investigate these transitions we have performed Monte Carlo simulations of a bond fluctuation model with Wang-Landau and umbrella sampling algorithms in a two-dimensional state space. The simulations' density-of-states results have been evaluated for interaction parameters spanning the range from good- to poor-solvent conditions and from repulsive to strongly attractive surfaces. In this work, we describe the simulation method and present results for the overall phase behavior and for some of the transitions. For adsorption in good solvent, we compare with Metropolis Monte Carlo data for the same model and find good agreement between the results. For the collapse transition, which occurs when the solvent quality changes from good to poor, we consider two situations corresponding to three-dimensional (hard surface) and two-dimensional (very attractive surface) chain conformations, respectively. For the hard surface, we compare tethered chains with free chains and find very similar behavior for both types of chains. For the very attractive surface, we find the two-dimensional chain collapse to be a two-step transition with the same sequence of transitions that is observed for three-dimensional chains: a coil-globule transition that changes the overall chain size is followed by a local rearrangement of chain segments.

Phase diagrams of knotted and unknotted ring polymers

“…Our simulation approach involves the detailed determination of the phase diagram for a single ring polymer, using a Monte Carlo method that determines the density of states for the entire accessible range of energies and confinement in one go. Similar examples of this approach have appeared before, notably in studies of peptide and polymer collapse, crystallization, adsorption and confinement [22][23][24][25][26][27][28][29][30][31][32][33][34][35], both on-and off-lattice.…”

Conformation and dynamics of a diluted chain in the presence of an adsorbing wall: A simulation with the bond fluctuation model

“…We studied the adsorption with different values for the wall potential and different thermal treatments. As we are interested in chain dynamics, the BFM [25] with the Metropolis criterion [13] is preferred over other methods as the Wang-Landau, which is more appropriate for equilibrium properties or phase transition studies [19,26]. The main aim of this study is to analyze the behaviour of a semiflexible chain in a confined space and in presence of an adsorbing wall in order to obtain a deeper insight in the morphology of the system.…”

Studying the Adsorption of Polymers and Biomolecules on Surfaces Using Enhanced Sampling Methods

“…The simulation of lattice polymers and peptides has been a fruitful area for the development of accelerated simulation methods in recent years [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The essential ideas behind the current work have been presented already in the context of the HP model and the simulation of confined ring polymers [21][22][23][24], so only a brief summary will be given here.…”

“…To counter this, and ensure that the system has "regularized" thermodynamic behavior, two approaches are in common use. The first is to study a system in which one end of the polymer is permanently "tethered" or "grafted" to the surface [12][13][14][15][16]. This has the disadvantage of being different from the physical system of interest, in many cases, namely adsorption of free molecules from the bulk.…”