A. Sariban

Critical properties of the Flory–Huggins lattice model of polymer mixtures

Monte Carlo simulations are presented for a model of a symmetrical polymer mixture on the simple cubic lattice, modeling both polymers A, B by self‐avoiding walks of NA=NB=N steps. If a pair of nearest‐neighbor sites is taken by monomers of the same species, an energy e is won. In the Monte Carlo algorithm local motions of the chains are considered (allowing for 20% vacancies to ensure enough chain mobility) as well as transformations of A chains into B chains and vice versa, since the simulation applies the grand‐canonical ensemble where the chemical potential difference rather than the volume fraction is fixed. The phase diagram, the excess specific heat, and the structure factor in the long‐wavelength limit are obtained for N=4, 8, 16, and 32 using finite L×L×L lattices with L ranging from 8 to 20. Analyzing these results with finite size scaling techniques, both critical exponents and critical amplitudes are estimated. Although the exponents are consistent with those of the three‐dimensional Ising mod...

Polymer chain dynamics derived from the Kramers potential: A treatment of the Rouse model with and without excluded volume interaction

We suggest that at least for single polymer chains relaxation times of typical dynamical processes can be obtained from biased sampling Monte Carlo computations on equilibrium data. We show this explicitly for the viscosity difference relaxation time τ in the Rouse or Zimm model (with any suitable, iterated or not, preaveraging of the Oseen–Burgers tensor) chain. We briefly discuss the corrections of such theory due to the excluded volume effect. We illustrate by performing the biased average of the equilibrium radius of gyration of Rouse chains of up to 150 monomer beads on a cubic lattice which yields directly τ.

Monte Carlo simulation of a lattice model for ternary polymer mixtures

Monte Carlo studies of symmetrical polymer mixturesAB, modelled by selfavoiding walks withNA=NB=N steps on a simple cubic lattice, are presented for arbitrary concentrations of vacanciesφv in the range fromφv=0.2 toφv=0.8 and chain lengthsN≤64. We obtained the phase diagrams and the equation of state for three choices of the ratio ∈ / ∈AB (∈ being the energy between monomers of the same kind, ∈AB being the energy between different monomers). Flory-Huggins theory provides only a qualitative understanding of these results. If the equation of state is “fitted” with an effective Flory-Huggins parameterχeff, the latter turns out to be strongly dependent on both concentration and temperature.

Scattering from concentration fluctuations in polymer blends: a Monte Carlo investigation

AbstractThe collective scattering function Scoll(

Phase separation of symmetric polymer mixtures in a common good solvent in the semidilute concentration regime

\vec q

Phase separation of polymer mixtures in the presence of solvent

), which describes light (neutron-, x-ray) scattering under wavevector

Interaction effects on linear dimensions of polymer chains in polymer mixtures

\vec q