We study the compatibilizing effect of copolymers of different architectures on the interface between two incompatible polymer phases by dissipative particle dynamics. Three base polymer systems are investigated, namely weakly incompatible (interspecies repulsion parameter of the dissipative particle dynamics interaction α AB : 25 < α AB < 30), intermediate-incompatible (30 ≤ α AB < 40), and strongly incompatible systems (α AB ≥ 40). We find that the compatibilization efficiency of all regular block copolymers in strongly incompatible systems can be predicted by a power-law function, which contains the Flory−Huggins interaction parameter, the areal concentration, and the mean block length of the compatibilizer. Regular multiblock copolymers have better compatibilization performance compared to the symmetric diblock copolymers at the same areal concentration. This is because smaller amounts of the multiblock copolymer are required to saturate a given interfacial area. For unsymmetric diblock copolymers in strongly incompatible systems, we find additionally that the length of the shortest block is a more important determinant for the compatibilization efficiency than the ratio of block lengths. Our work reveals the involved mechanisms of the compatibilization process, and it provides a promising route to predict the compatibilization efficiency of differently structured copolymer additives in the respective polymer blends.
We investigate polymer precipitation dynamics using explicit-solvent dissipative particle dynamics. We present a method to partially exchange solvent by antisolvent. In a first set of simulations, we analyze the collapse of a single chain of 25 beads as both liquids are mixing. The variation of the chain's mean-squared radius of gyration during collapse is found to be strongly influenced by the distance that the antisolvent must diffuse to the chain. This behavior is validated using an analytical model. We further report inclusion of solvent in the collapsed chains in equilibrium as well as the formation of a solvation layer. The influence of slip-springs and thus entanglements on the collapse of a single chain of 100 beads is evaluated in a second set of simulations. We did not find any influence of entanglements on the chain's collapse nor can we report a two-stage collapse process when enforcing these self-entanglements onto the chain.
Graft copolymers are widely used as compatibilizers in homopolymer blends. Computational modeling techniques for predicting the compatibilization efficiency of such polymeric materials have substantially accelerated their development. We employ an efficient particle-based simulation method, namely dissipative particle dynamics (DPD), to systematically investigate the compatibilization efficiency of graft copolymers for a wide range of design parameters such as polymer chemistry, backbone and side chain lengths, and the number of side chains. We find that regular graft copolymers (with regular side chain distribution) exhibit different compatibilization efficiencies at the same areal concentrations. This indicates that the molecular architecture plays a critical role in their compatibilization efficiency. To understand these observations, detailed analysis has been performed. Specifically, the relative shape anisometry of the graft copolymers, which is defined as the ratio of their gyration tensor elements in directions normal and parallel to the surface, is found to be strongly correlated to their compatibilization efficiency. Furthermore, we have investigated three specific graft copolymer types, namely, double-end-grafted (side chains concentrated near both chain ends of the backbone), mid-grafted (side chains concentrated on the center of the backbone), and single-end-grafted (side chains only concentrated near one end of the backbone), to understand the influence of varying side chain distributions. Compared to all other series, the mid-grafted copolymers exhibit the best compatibilization efficiency. Combining the obtained DPD results with five models of machine learning (ML), including linear regression (LR), elastic net (EN), random forest (RF), extra tree (ET), and gradient boosting (GB), provides effective predictions for the compatibilization efficiency. The GB model, which yields the best accuracy, has been further used to acquire the feature importance rank (FIR). Starting from these ML models and the FIR analysis, we have developed a framework for fast predictions of the compatibilization efficiency of graft copolymers. This novel framework utilizes physical insights into effects of material properties, such as chemistries and molecular architectures, on the compatibilization efficiency of graft copolymers and paves the way for advanced design of polymer compatibilizers.
In the present work, the optical response of isolated (CdSe) n + clusters with n = 3–6 is probed by measuring the photodissociation cross section in the photon energy range ℏω = 1.9–4.9 eV. In this joint experimental and theoretical study, the experimental observations are analyzed with time-dependent density functional theory and equation-of-motion coupled cluster theory. Structural candidates for the time-dependent excited-state calculations are obtained via global optimization by employing a genetic algorithm. The combined experimental and theoretical approach allows the discrimination of cluster geometries in the molecular beam experiments. From n ≥ 5, three-dimensional structures are found. Already for n = 6, light absorption in the red spectral range is observed. This observation is discussed with respect to the size dependence of the optical behavior of finite systems taking experimental and theoretical work on bare and ligated CdSe clusters and nanoparticles into account. Particularly, the influence of the net charge and ligands is considered. This allows a detailed discussion of the size-dependent evolution of the optical properties starting from molecular species over to nanoclusters and nanoparticles and finally to bulk CdSe.
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