A Hybrid Monte Carlo Self-Consistent Field Model of Physical Gels of Telechelic Polymers

We
developed a hybrid Monte Carlo self-consistent field technique
to model physical gels composed of ABA triblock copolymers and gain
insight into the structure and interactions in such gels. The associative
A blocks of the polymers are confined to small volumes called nodes,
while the B block can move freely as long as it is connected to the
A blocks. A Monte Carlo algorithm is used to sample the node configurations
on a lattice, and Scheutjens–Fleer self-consistent field (SF-SCF)
equations are used to determine the change in free energy. The advantage
of this approach over more coarse grained methods is that we do not
need to predefine an interaction potential between the nodes. Using
this MC-SCF hybrid simulation, we determined the radial distribution
functions of the nodes and structure factors and osmotic compressibilities
of the gels. For a high number of polymers per node and a solvent-B
Flory–Huggins interaction parameter of 0.5, phase separation
is predicted. Because of limitations in the simulation volume, we
did however not establish the full phase diagram. For comparison,
we performed some coarse-grained MC simulations in which the nodes
are modeled as single particles with pair potentials extracted from
SF-SCF calculations. At intermediate concentrations, these simulations
gave qualitatively similar results as the MC-SCF hybrid. However,
at relatively low and high polymer volume fractions, the structure
of the coarse-grained gels is significantly different because higher-order
interactions between the nodes are not accounted for. Finally, we
compare the predictions of the MC-SCF simulations with experimental
and modeling data on telechelic polymer networks from literature.