Scaling Behavior of Polymers at Liquid/Liquid Interfaces

Abstract

The dynamics of a polymer chain confined in a soft 2D slit formed by two immiscible liquids is studied by means of molecular dynamics simulations. We show that the scaling behaviour of a polymer confined between two liquids does not follow that predicted for polymers adsorbed on solid or soft surfaces such as lipid bilayers. Indeed our results show that in the diffusive regime the polymer behaves like in bulk solution following the Zimm model and with the hydrodynamic interactions dominating its dynamics. Although the presence of the interface does not affect the long-time diffusion properties it has an influence on the dynamics of at short-time scale where for low molecular weight polymers the subdiffusive regime almost disappears. Simulations carried out when the liquid interface is sandwiched between two solid walls show that when the confinement is few times larger than the blob size the Rouse dynamics is recovered.

Cross-over in the dynamics of polymer confined between two liquids of different viscosity

“…Again the results indicate a shift from a Zimm-like dynamics to a Rouse dynamics (where the exponent is 3.3 in two dimensions) upon increasing the viscosity of one of the fluids. It is interesting to notice that the exponent calculated for the interfacial system with Q h ¼ 1 [28] is again smaller (2.80) than those obtained here and also than the ones predicted by theory. We ascribed this result to the fact that the density of the liquid at the interface is smaller than in the bulk and its dynamics is faster [28], reducing the drag force exerted by the solvent beads on the polymer.…”

“…We obtain z ¼ 2.37 + 0.03 for the system with Q h % 1.5 and z ¼ 2.55 + 0.14 for the system with Q h % 50. In both cases, the exponents are larger than that predicted by the Zimm model (z z ¼ 2.19), which includes HI and describes the dynamical behaviour of polymer in dilute solution, and it is also larger than the value obtained for polymer chains at the interface between two liquids with the same viscosity (Q h ¼ 1) (z ¼ 2.05) [28]. Our results therefore indicate that increasing the viscosity of one of the two fluids changes the dynamics of the polymer chain and leads to a gradual transition from a Zimm-like dynamics to a Rouse dynamics (z R ¼ 2.54) where HI are screened.…”

“…As in our previous work [28], the simulated systems consisted of a single polymer chain located at the interface of two immiscible fluids [4,28]. The polymer chain was modelled as a bead-andspring chain where non-bonded interactions between the polymer beads were described using the cut and shifted Lennard-Jones (LJ) potential (equation (2.1)) with a cut-off distance of r c ¼ 2 1/6 s:…”

Comparison of equilibrium techniques for the viscosity calculation from DPD simulations

“…This section analyses the viscosity values calculated from the DPD simulations and verifies that our revised Einstein formula can reproduce the rheological behaviour predicted by polymer theory. The scaling of the dynamical properties with the polymer molecular weight is used in polymer physics to determine whether the polymer solutions follow the Rouse or Zimm theoretical model 3,51 . The scaling of these quantities can be found using a linear fit and the value of the exponent is characteristic of the system's dynamic behaviour.…”

MARTINI coarse‐grained model for poly‐ε‐caprolactone in acetone‐water mixtures

“…[8] Due to the large time and length scales involved in many biological and soft matter applications, the solely atomistic MD cannot provide complete insight into such complex systems. Coarse-grained molecular dynamics (CGMD) is then needed in order to reduce the number of degrees of freedom (DOF), [9][10][11][12] by grouping a given number of atoms together in a unique particle denominated "bead." Thanks to the possibility of simulating larger systems for very long times, CGMD is becoming increasingly popular in the investigation of many biological and complex systems, such as proteins, [13] DNA, [14] and lipids.…”