Adsorption of polymers on a brush: Tuning the order of the wetting phase transition

Abstract

We develop a computational methodology for the direct measurement of a wetting transition and its order via the effective interface potential. The method also allows to estimate contact angles in the nonwet state and to study adsorption isotherms. The proposed methodology is employed in order to study the wetting behavior of polymers on top of a brush consisting of identical polymers. In the absence of long-range forces, the system shows a sequence of nonwet, wet, and nonwet states as the brush density is increased. Including attractive long-range interactions we can make the polymer liquid wet the bush at all grafting densities, and both first- and second-order wetting transitions are observed. The latter case is limited to a small interval of grafting densities where the melt wets the brush in the absence of long-range interactions. Second-order wetting transitions are preceded by a first-order surface transition from a thin to a thick adsorbed layer. The interval of second-order wetting transitions is limited at low grafting densities by a surface critical end point and at high grafting densities by a tricritical wetting point. Our study highlights the rich wetting behavior that results when competing adsorbent-substrate interactions of different scales are tuned over a broad range.

Mesoscopic Hamiltonian for the fluctuations of adsorbed Lennard-Jones liquid films

“…We compare the results for the lateral size of L x = 10.457σ used in our previous work [22] for sf = The effective wall potential on the film thickness was obtained from MC simulations in the grand-canonical ensemble but with a shifting restriction on the total number of particles, to get overlapping probability distributions that could be merged into a single function (ξ ). This method [28,29] provides a good statistical sampling over the whole range of film thickness presented in Fig. 1.…”

“…The procedure, following the previous works of MacDowell and Müller [28,29], was explained in our previous paper [23], with two alternative method to determine the mean thickness of the wetting film (see Appendix). The simplest is the Gibbs' dividing (GD) plane, withξ = ξ N determined by the instantaneous number of particles, the second estimation of the mean thickness,ξ = ξ IS , is based on the intrinsic surface (IS) at the edge of the layer, as given by the ISM with a percolation analysis and the identification of the outermost liquid layer.…”

Comparison of dissipative particle dynamics and Langevin thermostats for out-of-equilibrium simulations of polymeric systems

“…The equilibrium properties of these reference systems are interesting and have been comprehensively studied in previous works 4,15,20,21,22,23,24 . The brush layers are characterized by the number of grafted chains per unit area or grafting density ρ g .…”

Changes in the structure of tethered chain molecules as predicted by density functional approach

“…The studies included scaling theories [13][14][15], classical self-consistent field methods [16,17], single chain mean-field methods [18], density functional theories [18][19][20][21][22] and computer simulations [23][24][25][26][27][28][29][30][31][32][33][34]. In our opinion, particularly important for further theoretical studies of systems involving tethered chains is the development of density functional theory (DFT) [20,21,[35][36][37][38][39][40][41][42] that is based on the approach proposed by Yu and Wu [43].…”