No abstract

A Gaussian chain model of poly (styrene)-poly (isoprene) (PS-PI) block copolymer with a dissipative particle dynamics (DPD) simulation was employed to study the formation of specific characteristic structures such as body-centered-cubic (BCC), hexagonal packed cylinders (HPC), ordered bicontinuous double diamond (OBDD), and lamellar (LAM) via order-disorder transition (ODT). The BCC, HPC, OBDD and LAM microphases were then subjected to thermal cycles of heating and cooling. The order-order phase transition (OOT) from HPC to BCC was monitored and two new transitions, OBDD to LAM and LAM to hexagonal perforated layers (HPL), were detected during the thermal process. Two metastable states (cylinders and HPL) were observed in the OOT process from the OBDD to LAM microphases. It is shown that all order-order transitions between the different kinds of structures are thermoreversible. The results were compared with the predictions of recent theories and with available experimental outcomes and thus provide a test for the predictions of BCC, OBDD, and LAM microphases.

Mesoscopic simulations of linear and 3-arm star poly(styrene)-poly(isoprene) block copolymers was performed using a representation of the polymeric molecular structures by means of Gaussian models. The systems were represented by a group of spherical beads connected by harmonic springs; each bead corresponds to a segment of the block chain. The quantitative estimation for the bead-bead interaction of each system was calculated using a Flory-Huggins modified thermodynamical model. The Gaussian models together with dissipative particle dynamics (DPD) were employed to explore the self-organization process of ordered structures in these polymeric systems. These mesoscopic simulations for linear and 3-arm star block copolymers predict microphase separation, order-disorder transition, and self-assembly of the ordered structures with specific morphologies such as body-centered-cubic (BCC), hexagonal packed cylinders (HPC), hexagonal perforated layers (HPL), alternating lamellar (LAM), and ordered bicontinuous double diamond (OBDD) phases. The agreement between our simulations and experimental results validate the Gaussian chain models and mesoscopic parameters used for these polymers and allow describing complex macromolecular structures of soft condensed matter with large molecular weight at the statistical segment level.