Monte Carlo Simulation Of The Effect Of Polydispersity On The Self-assembly Behavior Of Block Copolymers

Monte Carlo simulation was used to study the effect of molecular weight distribution andcomposition distribution on the self-assembly behavior of diblock copolymers. There are twokinds of systems in this study. One of them is called polydisperse symmetric diblockcopolymer. In this system it contains three length-different subcomponents which are L1 = 6,L2 = 30 and L3 = 54, all of the subcomponents are symmetric. The polydisperse diblockcopolymer system was constructed by mixing three different symmetric diblock copolymerchains in length and keep the number average molecular weight as a constant ( M n= 30). IPDIranges from 1.0 to 1.6. The other system is called asymmetric diblock copolymer. In thissystem the chain length of the copolymers is constant ( L = 30) but it has a compositiondistribution. There are three different ratios of the length of A block and B block whichare R1 = 3:1, R2 = 1:1 and R3 = 1:3. The polydisperse diblock copolymer systems wereconstructed by mixing three different asymmetric diblock copolymer chains. Take A block forinstance, the bigger the IPDI of A block is the broader the composition distribution is. The IPDIof A block ranges from 1.0 to 1.4 in this study.The simulation was performed in two (periodical, parallel wall and circle) andthree-dimensional (spherical and cylindrical) space, respectively. The results indicate that inthe both two systems the phase domain size increases with the increase of IPDI both in 2D and3D space. Moreover, increasing IPDI (or composition distribution) can induce order to disordertransition for the diblock copolymers confined by parallel wall in 2D. More important is thatthe system changed from well ordered core-multishell to a new well ordered core-multishellstructure with increasing polydispersity index (PDI) or IPDI if the copolymers were confined ina circle, sphere or cylinder. Comparing these two core-multishell structures, it was found thatone shell was lost and the core was occupied by the other component with increasingpolydispersity.