Computer simulations in block copolymers, charged colloidal particles and polyelectrolytes
In this work, nano-structures of block copolymer melts, self-assembling between charged nano-particles and polyelectrolytes were investigated by computer simulations. In the first chapter, the developments in the fields of microphase separation in block copolymers and self-assembling of polyelectrolytes were introduced in general. In chapter 2, a modified bond-fluctuation and vacancy diffusion lattice Monte Carlo algorithm were presented. By employing this algorithm, the morphologies of ABA and ABC triblock copolymer melts confined in two parallel walls were studied in chapters 2 and 3 respectively. In ABA triblock copolymer melts, parallel lamellae, perforated lamellae, mesh-like morphologies and normal lamellae as well as parallel cylinders and normal cylinders were identified. In ABC triblock copolymer melts, ABCCBA alternate lamellae, "tricolor checkerboard like" morphology and other special morphologies were observed. In chapters 4 and 5, employing Monte Carlo simulations, the effects of confinements from the nano-cylindrical tube on the copolymer morphology were investigated. In chapter 4, the morphology transitions in AB diblock copolymer melts were examined in detail and a variety of helical morphologies and complex mesh morphologies were found. In chapter 5, much more novel morphologies were identified in ABC triblock copolymer melts. In chapter 6, a mesoscopic approach, cell dynamic system (CDS) was extended to diblock copolymer melts in electric fields and the coupled orthogonal electric and shear fields. The long-range lamellae and cylinders, which cannot be obtained under the surface field, were achieved in AB diblock copolymer melts by applying above long-range external fields. Furthermore, the dynamics of pattern evolution of AB diblock copolymer melts were also studied in chapter 6. In chapter 7, the effective potentials between particles subjected to van der Waals and electrostatic pair interactions were calculated by off-lattice Monte Carlo simulations. The simulation results have shown that an effective attractive interaction can be generated even though there was no attractive component in the pair potential employed because of many-body effects. In chapter 8, off-lattice Monte Carlo simulations were applied to examine the adsorption of a single polyampholyte on a single charged nano-particle. The simulations revealed that there are three conformation regimes of the complex. When both of the charge density and the particle size were small, the chain kept largely the configurations, which it would have had when it was alone in the bulk. By increasing the charge density and the particle size, the polyampholyte chain collapsed on the surface of the particle. A further increase of the above two factors leaded to a separation between the subchains with positive and negative charges. In chapter 9, self-recognition between diblock polyelectrolytes was studied. Both matched lengths and charge numbers were important factors in the process of self-recognition. Furthermore, matching chains can form larger and tighter aggregates, with more coiled chains than those in unmatched aggregates or network structures.