Molecular Dynamics Simulation Of Electric-field-induced Self-assembly Of Diblock Copolymers

The self-assembly of block copolymers under an external electric field was studied with a coarse-grained polarizable model that hybridizes the conventional polymeric coarse-grained model and Drude oscillator.The polarizability of the coarse-grained polymeric segment was reflected by the Drude oscillator,i.e.,a positive core particle and a negative shell particle are connected by a spring.When the electric field is absent,the shell and coarse-grained beads coincide with each other;while the electric field is imposed,the shell and coarse-grained bead are separated,showing the polarizability.As a result,our model not only can simulate the microphase separation of block copolymer melts without an electric field but also can further show the polarizable behavior and its influence on phase structures when an external electric field is imposed.Based on this model,we use the Langevin dynamics method to study the the self-assembly of block copolymers.the alignment of the lamellar phase of the block copolymer melt under an external electric field was observed and the dynamic coupling information between chain polarization and interface orientation induced by the external electric field was obtained.It is demonstrated that the alignment of the lamellar structure along the electric field direction results from the polarizability difference of the polymer components.The sphere-to-cylinder transition was further studied using our polarized CG model under the electric field.spheres elongate then interconnect to form cylinders paralle to the direction of the electric field.Finally,the transitions of phase structures of the block copolymer under an external electric field,from gyroid structure to cylindrical phase,and from gyroid structure to lamellae phase were simulated.Our simulations demonstrate that the present CG polarized model can effectively simulate the phase transition and provide valuable information on a molecular level.