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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.

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In this work, the drug release mechanism of a polymeric delivery vehicle (polymeric microsphere) is investigated using dissipative particle dynamics (DPD) simulations. Polymer nanoparticles are interesting drug-delivery systems because drugs can be encapsulated inside the shell, which exhibits swelling properties that depend on pH conditions. Albendazole is selected as the model drug, whereas poly(styrene-divinylbenzene) P(ST-DVB) copolymer is the carrier. The DPD simulation shows that drug release of the P(ST-DVB) carrier in an acidic environment occurs via a diffusion mechanism (swelling followed by diffusion). Four transient stages were detected during the drug release: (i) swelling of the polymeric microsphere, (ii) the generation of pores, (iii) drug diffusion in the polymeric matrix and (iv) drug release towards the acid medium. All transient states of the drug release process of the polymeric carrier in an acid environment are described and analysed in this paper. The outcomes obtained from the DPD simulations are consistent with the available experimental results, and they provide a mesoscopic methodology for the evaluation and prediction of new advanced polymeric carriers of pharmaceutical interest.

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We simulated the thermoreversible micellization-demicellization process and micellar shuttle of a poly (N-isopropylacrylamide-block-ethylene-oxide) (PNIPAM-PEO) diblock copolymer in a water/ionicliquid (1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF 6 ]) system by means of dissipative particle dynamics (DPD). The evolution of diblock copolymer chains (micellizationtransfer-demicellization) in both water and the ionic liquid phase by the temperature effect reveals that it is a physical phenomenon, dependent on the solubility and interaction parameters of all chemical species involved in the multicomponent system. With the aid of a Monte Carlo simulation we calculated the Flory-Huggins interaction parameters c of all the species. At room temperature the PNIPAM-PEO copolymer chains are miscible in the aqueous phase. At a higher temperature of T ¼ 303 K the diblock copolymer shows the formation of micelles (micellization process). The micellar transfer to the ionic liquid phase was observed at T ¼ 333 K. A further increase in temperature provokes the demicellization at T ¼ 346 K. The process is reversible: reversing the temperature now to 333 K, shows the formation of the micelles. A further decrease in temperature makes the micelles go back to the water phase. All the simulation outcomes are qualitatively consistent with the experimental results, demonstrating that the DPD methodology may provide a tool for the investigation and analysis of the micellar transfer process in immiscible environments.

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