(192a) Comparison of PRISM Theory and Molecular Dynamics Simulations for Studying Assembly in Block Copolymer Solutions of Varying Sequences and Composition | AIChE

(192a) Comparison of PRISM Theory and Molecular Dynamics Simulations for Studying Assembly in Block Copolymer Solutions of Varying Sequences and Composition

Authors 

Lyubimov, I. - Presenter, University of Delaware
Beltran-Villegas, D. J., University of Delaware
Jayaraman, A., University of Delaware, Newark
In this poster, we will present our recent work directly comparing Polymer Reference Interaction Site Model (PRISM) theory and molecular dynamics (MD) simulations for studying assembly of amphiphilic block copolymers in solution. In both methods, we use a generic coarse-grained model to represent amphiphilic AB block copolymers in implicit solvent with the solvophobicity of the B block captured using effective B-B attractions modeled using Lennard Jones potential. We study the assembly of the amphiphilic AB block copolymer as a function of solvophobicity for varying copolymer sequences (diblock and triblock) and composition (solvophobic-rich or solvophilic-rich). We then solve the PRISM theory equation along with Percus Yevick closures for these block copolymer solutions and obtain the inter-molecular pair correlations in real space, g(r), and structure factors in Fourier space, S(k), at increasing values of solvophobicity. We directly compare the real-space intermolecular pair correlation functions and structure factors from PRISM theory and MD simulations. These structural results show excellent agreement between PRISM predictions and MD simulations at low solvophobicities. While PRISM theory captures the concentration fluctuations at low solvophobicities well, the intrinsically isotropic PRISM theory fails to converge to a numerical solution at higher solvophobicities where we see evolution of the assembled structures in MD simulations. Despite this drawback, PRISM theory is a valuable tool as we can use the low solvophobicity results from PRISM to predict all or most of the thermodynamic signatures of the polymer solutions at higher solvophobocities. For example, the inverse microphase peak 1/S(k*) at low solvophobicity from PRISM theory when extrapolated to zero quantifies the disorder-order transition solvophobicity value in good quantitative agreement with MD simulations. Additionally, in the systems where MD simulations predict aggregation of the micelles/clusters at high solvophobicity, the structure factors from PRISM theory results at low solvophobicity also present an up-turn in the zero-wave vector structure indicating tendency for macrophase separation at higher solvophobicity. These findings provide evidence of the capability of PRISM theory for predicting copolymer assembly in solution, where a wide range of design parameters can be explored much faster than MD simulations.