The condensation of DNA induced by spermine is studied by atomic force microscopy （AFM） and molecular dynamics （MD） simulation in this paper. In our experiments, an equivalent amount of multivalent cations is added to the DNA solutions in different numbers of steps, and we find that the process of DNA condensation strongly depends on the speed of adding cations. That is, the slower the spermine cations are added, the slower the DNA aggregates. The MD and steered molecular dynamics （SMD） simulation results agree well with the experimental results, and the simulation data also show that the more steps of adding multivalent cations there are, the more compact the condensed DNA structure will be. This investigation can help us to control DNA condensation and understand the complicated structures of DNA--cation complexes.
The phase behaviours of a lamellar diblock copolymer/nanorod composite under steady shear are investigated using dissipative particle dynamics. We consider a wide range of nanorod concentrations, where the nanorods each have a preferential affinity to one of the blocks. Our results suggest that shear not only aligns the orientations of the diblock eopolymer templates and nanorods towards flow direction, but also regulates the distribution of the nanorods within the polymer matrix. Meanwhile, the shear-induced reorientation and morphology transitions of the systems also significantly depend on the nanorod concentration. At certain nanorod concentrations, the competitions between shearinduced polymer thinning and nanorods dispersion behaviours determine the phase behaviours of the composites. For high nanorod concentrations, no morphology transition is observed, but reorientation is present, in which the sheared nanorods are arranged into hexagonal packing arrays. Additionally, the orientation behaviour of nanorods is determined directly by the applied shear, also interfered with by the shear-stretched copolymer molecules.
The self-assembly of linear ABC triblock copolymers under cylindrical confinements is investigated in two- dimensional space using the real-space self-consistent field theory. The effects of confinement degrees and preferential strengths on the triblock copolymer phase behaviors with special polymer parameters are first considered. On one hand, different confinement degrees cause different phase behaviors in nanopores with the neutral surfaces. Moreover, the strongly preferential surface fields can surpass the confinement degrees and volume fractions in determing the confined phase behaviors. On the other hand, in contrast, confined morphologies are more sensitive to the variations in the A-preferential surface field strength. Subsequently, the incompatibility degrees between different blocks are systematically varied under cylindrical nanopore confinements. Under cylindrical nanopore confinements, the morphologies are very sensitive to the variations in the incompatibility degrees. Meanwhile, nanopore confinements can affect order-disorder and order-order transition points in the bulk. The corresponding free, internal, and entropic energies as well as the order parameters are also quantificationally examined to deeply investigate the confined phase mechanisms, and a number of morphological transitions are confirmed to be of first-order. These findings may guide the design of novel nanostructures based on triblock copolymers by introducing confinements.
